Protocol and Baseline Traits of the Monitoring in Dialysis Examine
Clin J Am Soc Nephrol. 2016 Apr 7; 11(4): 721–734.
Dialysis sufferers have excessive charges of cardiovascular morbidity and mortality, however knowledge on arrhythmia burden, arrhythmia sort, arrhythmia triggers, and the id of terminal arrhythmias have traditionally been restricted by an incapability to watch coronary heart rhythm for extended intervals.
To analyze arrhythmia and its affiliation with sudden dying in dialysis-dependent ESRD, describe the potential for implantable gadgets to advance research of dialysis physiology, evaluate the moral implications of utilizing implantable gadgets in scientific research, and report on the protocol and baseline outcomes of the Monitoring in Dialysis Examine (MiD).
Design, setting, contributors, & measurements
On this multicenter, interventional-observational, potential cohort research, we positioned implantable loop recorders in sufferers present process long-term hemodialysis. The proportion of sufferers experiencing clinically vital arrhythmias was the first endpoint. For six months, we captured detailed knowledge on the first endpoint, symptomatic arrhythmias, different electrocardiographic variables, dialysis prescription, electrolytes, dialysis-related variables, and very important indicators. We collected extra electrocardiographic knowledge for as much as 1 yr.
Total, 66 sufferers underwent implantation in websites in the USA and India. Diabetes was current in 63.6% of sufferers, 12.1% had been age ≥70 years, 69.7% had been males, and 53.0% had been black. Main and secondary endpoint knowledge are anticipated in 2016.
Cardiac arrhythmia is a crucial contributor to cardiovascular morbidity and mortality in dialysis sufferers, however obtainable know-how has beforehand restricted the flexibility to estimate its true burden and triggers and to outline terminal rhythms in sudden dying. Use of implantable know-how in observational research raises advanced points however might enormously develop understanding of dialysis physiology. Using implantable loop recorders in MiD is among the many first examples of such a trial, and the outcomes are anticipated to offer novel insights into the character of arrhythmia in hemodialysis sufferers.
Key phrases: scientific trial, heart problems, hemodialysis, arrhythmias, cardiac, cohort research, dying, sudden, coronary heart conduction system, people, kidney failure, continual, renal dialysis
Dialysis sufferers expertise excessive cardiovascular and all-cause mortality. The dying charge for all United States dialysis sufferers in 2011 was 198 per 1000 patient-years, with cardiac illness accounting for roughly 40% (1). Within the US Renal Information System database, two thirds of cardiac deaths are attributed to arrhythmia, making up 26% of mortality. Equally, within the Hemodialysis Examine and Die Deutsche Diabetes Dialyse Studie trials, 22% and 26% of deaths, respectively, had been sudden (2,3). Probably the most convincing validation of registry knowledge is supplied by the EValuation Of Cinacalcet HCl Remedy to Decrease CardioVascular Occasions research, the biggest randomized dialysis trial, which enrolled 3883 hyperparathyroid hemodialysis (HD) sufferers. Total, 25% of deaths had been adjudicated as sudden deaths (4), resolving hypothesis on the relative significance of (presumed) sudden cardiac dying (SCD) in HD sufferers ( and ) (1,4).
The underlying mechanisms of SCD, notably the precise sort of terminal arrhythmia (which has profound implications for prevention), stay controversial. Almost 5 years in the past, the Kidney Illness Enhancing World Outcomes Medical Replace Convention on heart problems in CKD presciently concluded, “Implantable loop recorders (ILRs) used to determine terminal arrhythmias might show helpful, however a coordinated effort could be vital given low enrollment charges anticipated in such research” (5). Moreover, the potential worth of ILRs will not be restricted to deadly arrhythmias—the detection of clinically unsuspected bradyarrhythmia and atrial fibrillation (AF) markedly widens their potential utility. On this manuscript, we evaluate knowledge on arrhythmia in HD sufferers and current the protocol and baseline knowledge from the Monitoring in Dialysis Trial (MiD), which used ILR to detect arrhythmia within the setting of HD.
Hemodialysis initiation is a time of markedly elevated threat. Wholesome Individuals (HP) is a federally mandated program established to enhance the well being of People; one main objective of HP2020 is to “cut back new instances of CKD and its issues, incapacity, dying, and financial prices” (1). Commensurate with the singularly excessive mortality charge in incident dialysis sufferers, the HP2020 CKD-14.2 objective is to cut back the dying charge throughout the first 3 months of dialysis initiation to 319.9 deaths per 1,000 patient-years (from the 2011 charge of 335.4 per 1000 patient-years). reveals the early hazard of SCD (and different cause-specific mortality) at dialysis initiation (6).
One main data hole in understanding of SCD in dialysis sufferers is ambiguity concerning the “terminal occasion,” notably in distinguishing between sudden dying as a consequence of arrhythmia and sudden dying not preventable with cardiac gadgets. Kidney Illness Enhancing World Outcomes (5) recognized the paucity of post-mortem knowledge in dialysis-related SCD as a serious data hole and highlighted the problematic nature of typical definitions: “sudden, surprising dying inside an hour of symptom onset, or unwitnessed, surprising dying with out apparent non-cardiac trigger in sufferers recognized to be effectively throughout the previous 24 hours.” What precisely is “surprising dying” in a inhabitants with a excessive burden of comorbid sickness who spend a disproportionate period of time in well being care amenities? Moreover, following withdrawal from dialysis, sufferers in the end die of terminal arrhythmias, however that is dying as a consequence of withdrawal. With out patient-centered context, one might simply (and wrongly) infer SCD because the “major” occasion from an ILR. Equally, such ailments as subarachnoid hemorrhage or aortic dissection might mimic SCD within the absence of rhythm tracings.
Many publications have highlighted methods for threat stratification to foretell SCD in dialysis sufferers. For instance, biomarkers indicating irritation and malnutrition (e.g., albumin) are related to SCD threat (7,8). Moreover (however maybe not surprisingly), there could also be heritability to SCD propensity in dialysis sufferers. Chan et al. lately reported that genetically associated members of the family on dialysis had a 1.7-fold improve within the odds of cardiac arrest in contrast with matched, unrelated controls (9). Within the common inhabitants, uncommon mutations in ionic channels trigger a number of distinct long-QT syndromes, that are related to a markedly increased threat of SCD (10). Nevertheless, polymorphisms in long-QT syndrome genes are comparatively frequent (roughly 1% of common inhabitants) (11). These genetic polymorphisms could also be extremely related and extra harmful within the context of typical HD given the fast declines in serum potassium, magnesium, and calcium, coupled with frequent publicity to medicine that trigger QT prolongation (corresponding to fluoroquinolones).
Typical 12-lead electrocardiography is an affordable methodology for evaluation of the QT interval and the QT interval corrected for coronary heart charge (a worth >460 msec for the latter is taken into account extended). Though measurement of QT dispersion as a predictor of threat has been studied in dialysis sufferers, its function in scientific observe remains to be unsure. Though ventricular arrhythmias (primarily untimely ventricular contractions) are frequent in dialysis sufferers (primarily based on 48-hour Holter monitoring), a potential research of 127 Italian HD sufferers adopted for 4 years confirmed they weren’t predictive of total mortality (12,13).
Few knowledge can be found on the sorts of deadly arrhythmias in dialysis sufferers. One paper detailed 84 sudden cardiac arrest occasions in dialysis sufferers with wearable cardioverter-defibrillators (14). On this chosen cohort, 78% of preliminary rhythms had been ventricular tachycardia (VT; 64.3%) or ventricular fibrillation (VF; 14.3%), and 21.4% had been asystole (i.e., not shockable). Unpublished knowledge (kindly equipped by Linda Becker) masking emergency medical providers knowledge on 47 cardiac arrests in 9 outpatient dialysis facilities in Seattle/King County between 1990 and 1996 confirmed that in 29 (62%) arrests the rhythm was VT or VF. A current Australian research utilizing ILRs, nevertheless, implicates bradycardia and asystole as the most important contributors to SCD in HD sufferers; this discovering suggests pump failure or noncardiac causes for the ultimate sequence of scientific occasions resulting in dying (15,16). An necessary caveat was the exceptionally lengthy dialysis classic of the research sufferers (imply±SD, 6±4 years); the kind of arrhythmia (and terminal occasion) is likely to be completely different in sufferers of newer versus older dialysis classic.
Position of Dialysis Baths
Low-potassium dialysate of 0 or 1 mEq/L (17) or <2 mEq/L (18) and decrease calcium dialysate (<2.5 mEq/L) (19) have been implicated as threat elements for SCD in massive database research. Equally, low serum magnesium ranges had been related to increased all-cause mortality in Japanese dialysis sufferers (20), however few knowledge exist on SCD threat and magnesium dialysate ranges.
Though nice enthusiasm exists amongst nephrology professionals for extra frequent upkeep HD, most sufferers dialyze thrice weekly, necessitating two gaps of 1 day and one hole of two days. This has lengthy been considered as physiologically difficult in sufferers with restricted capability to keep up homeostasis within the presence of metabolic and volume-related excursions from normality, the place background heart problems is the norm.
In a nationally consultant United States pattern between 2004 and 2007, one research in contrast charges of dying and cardiovascular admissions on the day after the 2-day interdialytic interval with charges on different days (21). As proven in , though total mortality, cardiovascular mortality, and cardiovascular admission charges had been increased on the day after the lengthy interval, relative occasion disparities had been particularly marked for congestive coronary heart failure (by an element of 1.8) and dysrhythmia (by an element of 1.9).
Related associations have been seen in a number of massive research (22–24). For instance, in a current research of newly incident HD sufferers in the UK between 2002 and 2006, hospital admission charges after the 2-day hole had been 1.7-fold increased, whereas all-cause mortality charges had been 1.22 instances increased. As with virtually all the literature to this point, this research was not particularly configured to check charges of SCD. Nonetheless, out-of-hospital dying charges had been 1.59 instances increased after the lengthy interval than after the shorter interval and only one.06 instances increased for in-hospital dying (23).
Pathophysiology of Arrhythmia in CKD
A number of cardiovascular threat elements, together with atherosclerotic coronary heart illness, left ventricular hypertrophy (LVH), and accelerated cardiac fibrosis, seem to contribute to arrhythmia pathogenesis in ESRD (25). Though arrhythmia and in the end sudden cardiac dying can happen in sufferers (within the common inhabitants) with apparently structurally regular hearts, most sufferers (notably these with CKD) have underlying structural coronary heart illness, and a few sort of acute occasion interacts with the underlying substrate to supply the deadly arrhythmia (26,27).
Though many triggers have been recognized, acute myocardial ischemia is felt to be the commonest initiating occasion within the common inhabitants (28). In sufferers with superior CKD (notably these present process dialysis), myocardial ischemia is more likely to be a contributor, however it’s also believable that myocardial ischemia (of the sort mediated by epicardial coronary artery illness) might play a much less predominant function and that different elements, corresponding to irritation and autonomic imbalance or elevated sympathetic exercise (together with sleep apnea), could also be necessary contributors to sudden cardiac dying (29,30). Hypertrophic myocardium is predisposed to each atrial and ventricular arrhythmia via the induction of extended motion potentials and elevated repolarization defects in areas of ischemia, with underling fibrosis serving as a positive substrate for propagation of arrhythmia. Whereas hypertension, diabetes, and different typical threat elements undoubtedly contribute, dialysis and uremia might straight contribute to LVH and fibrosis, which seems to speed up after dialysis initiation. In a potential research of 596 sufferers with ESRD who had no historical past of heart problems, for instance, serial echocardiography demonstrated that left ventricular mass index elevated considerably throughout the first 2 years of dialysis (31).
Processes distinctive to CKD and ESRD might largely account for rising left ventricular mass index. Mall et al. analyzed myocardial histology in sufferers with superior renal illness and famous that >90% of sufferers exhibited diffuse and uniform cardiac fibrosis with considerably larger ranges of myocardial collagen than noticed in hypertensive and valvular cardiomyopathies and diffuse moderately than the “patchy” fibrosis characterizing different circumstances (32). Amann et al. subsequently demonstrated that myocardial matrix enlargement was related to a discount of capillary density (33). Low capillary density might partly clarify sudden reductions in myocardial perfusion induced throughout dialysis. For instance, McIntyre et al. studied sufferers with ESRD who didn’t have vital coronary illness utilizing intradialytic place emission tomography and famous marked, regional reductions in myocardial perfusion throughout dialysis. Adjustments in perfusion had been accompanied by regional wall-motion abnormalities, suggesting that useful ischemia throughout dialysis will not be attributable to flow-limiting atherosclerosis (34).
The total pathogenesis of myocardial fibrosis and capillary rarefaction in ESRD is past the scope of this evaluate. Additional research is required to completely elucidate the pathways concerned. Nevertheless, a number of circulating elements, together with uneven dimethyl arginine (35,36), parathyroid hormone (37), aldosterone (38), fibroblast development factor-23 (39), angiotensin-2 (40), endogenous cardiac glycosides (41), vitamin D (42), and circulating angiogenesis inhibitors, have been implicated (35).
These observations counsel that along with the impact of LVH and coronary illness, transient myocardial ischemia induced by a mismatch between capillary provide and the hypertrophied myocardium could also be important to the era of arrhythmias (43). Conversely, myocardial fibrosis might gradual or disrupt regular conduction, resulting in bradycardia, asystole, and reentrant arrhythmias (43). Peridialytic modifications in BP, quantity standing, sympathetic tone, and electrolytes are more likely to additional contribute to arrhythmogenesis, however their actual contributions stay largely unstudied.
Incidence and Prevalence of AF
Though asystole or ventricular arrhythmias are the almost definitely sorts of arrhythmia to end in sudden dying, atrial arrhythmias, notably AF, might end in vital morbidity in sufferers with ESRD. AF is more and more frequent in HD sufferers. In a research of 258,605 older contributors, the AF incidence in incident dialysis sufferers was 14.8/100 person-years, and adjusted possibilities of creating AF throughout the first yr of dialysis elevated from 11.3% in 1995 to 14.3% in 2007 (44). Equally, the prevalence of AF (identified from administrative claims) was 10.7% in 2006—a three-fold improve from 1992 (45). Lastly, the general AF prevalence in a meta-analysis of 25 dialysis research was 11.6% (46).
Dialysis as a Set off
Most proof that HD triggers AF is oblique. Echocardiographic intra-atrial and interatrial activation instances, for instance, correlate with ultrafiltration quantity and shorten considerably towards the tip of HD (47). Equally, there are peridialytic modifications in P-wave dispersion (commonplace electrocardiography), P-wave period, and the foundation imply sq. voltage of the ultimate 20 ms of the filtered P wave (signal-averaged electrocardiography)—parameters that measure atrial conduction delay and are related to AF (48,49). In a number of research, intradialytic modifications had been outstanding and had been attenuated on the conclusion of dialysis (50,51). In others, modifications weren’t detected or had been seen solely on the conclusion of dialysis after which shortly attenuated (52). Nevertheless, in a single research, P-wave period decreased and root imply sq. voltage of the ultimate 20 ms of the filtered P wave decreased from the start to the tip of dialysis, modifications suggesting a diminished threat of AF after HD (53). Adjustments in electrolytes had been related to P-wave parameters in a number of research (51,52), however associations with ultrafiltration seem extra sturdy (50,51). On steadiness, this literature means that fast ultrafiltration or different elements throughout HD acutely have an effect on conduction in a method that would set off AF however that results quickly attenuate after HD.
Extra lately, implanted defibrillators had been used to watch sufferers enrolled within the Implantable Cardioverter Defibrillator-2 Trial. AF was detected in 14 of 40 dialysis sufferers—11 receiving HD, 3 receiving peritoneal dialysis, and 9 with out recognized AF (54). AF frequency was three-fold increased on dialysis days (P=0.001) however didn’t differ with period of the interdialytic interval. Intradialytic AF was 13-fold extra frequent than within the 7 hours earlier than dialysis (P=0.03) and two-fold increased than within the 7 hours after dialysis (P=0.001), though outcomes had been largely pushed by two sufferers. Decrease dialysate potassium focus and better ultrafiltration volumes had been related to AF prevalence. Extra lately, a trial utilizing an ILR in 50 HD sufferers discovered that the lengthy interdialytic interval was essentially the most frequent interval of arrhythmia. AF was detected in 42% of sufferers, and new-onset AF was asymptomatic in 86% (16).
Penalties of AF
Associations with stroke are related within the ESRD and common populations (44–46,55,56). In a current research, for instance, stroke incidence was 5.2/100 patient-years in sufferers with AF in contrast with 1.9/100 patient-years in dialysis sufferers with out AF (46). AF can also be strongly related to mortality as a consequence of deadly stroke and different causes, the speed of which is roughly doubled (26.9 versus 13.4/100 patient-years) when AF is current (44–46). As well as, AF is an unbiased threat issue for mesenteric ischemia, a regularly deadly occasion (57), and amputation (58); though this has not been studied within the setting of ESRD, AF might result in tachyarrhythmia-induced cardiomyopathy when sustained (59). Frequent AF might thus be an necessary reason for an prolonged array of morbidity and mortality, together with deadly stroke, coronary heart failure, and deterioration in LV ejection fraction in HD sufferers.
Relevance of Subclinical AF
Though associations of subclinical AF with scientific outcomes haven’t been studied in ESRD, a number of research counsel that clinically silent AF is a crucial stroke threat issue within the common inhabitants. In a single randomized pacemaker trial, the pacemaker monitoring operate was used to document fast atrial occasions (charge ≥220 beats/min [BPM] lasting ≥5 minutes) presumed to signify AF (60). Total, 51.3% of sufferers had occasions at a median onset of 100 days. Atrial occasions had been independently related to stroke (hazard ratio, 2.8; P=0.001). Different research have demonstrated related associations between subclinical AF and subsequent overt AF or stroke (61–63). Extra lately, the Cryptogenic Stroke and Underlying AF (CRYSTAL AF) (64) research randomly assigned 441 stroke sufferers with out AF who had been present process 24-hour monitoring to an ILR or typical follow-up. AF lasting >30 seconds was detected in 30% of intervention versus 3% of management sufferers at 3 years.
These knowledge counsel that subclinical AF is a crucial contributor to stroke whereas illustrating the bounds of scientific remark and commonplace diagnostics for advancing scientific discovery. In CRYSTAL AF, newly developed implantable applied sciences enabled long-term, steady monitoring, thereby facilitating discovery of a excessive frequency of “silent” AF and a paradigm shift within the understanding of cryptogenic stroke. Enhancing understanding of SCD and its affiliation with dialysis is an apparent extension. Extra broadly, CRYSTAL AF highlights a brand new paradigm through which the increasing capabilities and reducing measurement of wearable or implantable applied sciences will facilitate seize of beforehand unmeasurable parameters and assortment of extra granular physiologic knowledge, thereby enhancing understanding of dialysis physiology.
LINQ and Reveal XT System
Subcutaneous ILRs have been clinically obtainable since 1998 (Medtronic Reveal; Medtronic, Minneapolis, MN), and ILR use for detecting coronary heart rhythm abnormalities in sufferers with syncope, palpitations, AF, and different circumstances through which arrhythmia is suspected has been effectively described within the literature. These small loop recorders are positioned within the subcutaneous house and are leadless. ILRs constantly document the guts rhythm, and when programmed alert standards are met for analysis of arrhythmia, the occasion is captured and saved till retrieved in individual or by way of distant residence monitoring. Most sufferers within the MiD research had a Medtronic Reveal XT ILR implanted, however lately enrolled sufferers obtained an up to date machine, the Medtronic Reveal LINQ (). These screens are implanted subcutaneously with a easy outpatient process utilizing native anesthesia. In sufferers with out ESRD, device-related issues related to ILR implantation embody an infection (1.2%), machine migration, and ache on the implant web site (<1%) (65). Battery life is roughly 3 years, and each gadgets are conditionally permitted for magnetic resonance imaging (1.5 and three.0 T) with out reprogramming, though ready for six weeks after insertion with the XT machine is advisable (65,66). Medicare reimbursement for an ILR is mostly within the vary of $6000–$7000, which incorporates the machine and insertion-related prices.
Each Reveal XT and Reveal LINQ can detect and document AF in addition to residence monitoring capabilities, however the LINQ machine is 87% smaller (a couple of one third the dimensions of a triple-A battery), affords extra reminiscence (20% extra), and supplies automated nightly downloads of detected arrhythmias. Whereas Reveal XT required holding a landline-connected transmitter over the chest wall, automated nightly downloads from the LINQ monitor to a bedside cellphone–primarily based monitor (MyCareLink monitor [Medtronic, Minneapolis, MN]), enable every day evaluation of affected person’s coronary heart rhythms (). This functionality permits physicians to observe sufferers every day as an alternative of receiving the info solely when the affected person has signs or on the time of scheduled interrogation, as was the observe with the XT machine.
ILRs supply the flexibility to watch sufferers for an prolonged interval (as much as 3 years) (65). For sufferers with rare signs or who require long-term rhythm analysis, these screens present extra info than shorter-term Holter monitoring, wearable patch know-how, exterior loop recorders, or intermittent monitoring gadgets (67). Affected person compliance may be challenge with exterior screens, which limits their effectiveness (68).
The first goal of the MiD research (NCT01779856) was to estimate the proportion of HD sufferers experiencing clinically vital arrhythmias throughout a 6-month major remark interval utilizing the Reveal ILR system. Secondary targets had been to broadly characterize the prevalence of arrhythmia in HD-dependent ESRD and quantify associations with electrolytes, HD process, and quantity parameters.
Eligibility standards had been designed to maximise generalizability and affected person security (). All analysis complied with the Declaration of Helsinki and was permitted by relevant institutional evaluate boards.
|Inclusion Standards||Exclusion Standards|
|Age≥ 21 yr||Not appropriate for implantation (e.g., cachexia, extreme dermatologic circumstances)|
|In-center HD≥3 instances/wk or
eGFR<15 ml/min per 1.73 m2 with anticipated HD initiation inside 2 mo
|Anticipated survival <6 mo|
|Left-sided HD catheter in place anticipated to intrude with implantation|
|Skill to adjust to protocol||Thoracic surgical procedure inside 6 mo|
|An infection with 14 d|
|Bacteremia inside 60 d|
|Hemoglobin <10 g/dl on consecutive measurements inside prior 2 mo|
|Transplantation anticipated inside 6 mo|
|Modality switch anticipated inside 6 mo|
|Current pacemaker or ICD|
Echocardiography (if not carried out throughout the previous 6 months), 12-lead electrocardiography, medical historical past, and medicines had been obtained at baseline, and ILRs had been implanted inside 14 days. For the primary 6 months after implantation, sufferers transmitted Reveal knowledge instantly earlier than all dialysis classes and after every session related to a research blood draw. Postmortem transmission was inspired however was not particularly required by the protocol. Signs, dialysis prescription, ultrafiltration volumes, and peri- and postdialysis very important indicators had been collected at each dialysis session throughout the first 6 months. Blood was drawn each earlier than and after dialysis: twice weekly for 4 weeks and as soon as weekly thereafter via 6 months ( and ). After 6 months, transmissions occurred no less than weekly however knowledge assortment was in any other case restricted to opposed occasions.
|Weekly Session||First Session Predialysis||First Session Postdialysis||Second or Third Session Predialysis||Second or Third Session Postdialysis|
|Wk 5–26||Bb or C||D|
|Mind natriuretic peptide||Albumin||Albumin||Albumin||Albumin|
|Excessive-sensitivity C-reactive protein||Calcium||Calcium||Calcium||Creatinine|
Examine coordinators reviewed transmissions after the dialysis session to determine prespecified, doubtlessly harmful arrhythmias, which mandated investigator evaluate: VT ≥180 BPM for >15 seconds, asystole >5 seconds, waking (6 a.m.–10 p.m.) coronary heart charge ≤40 BPM for ≥6 seconds, AF for >24 hours or for >12 hours over consecutive days, or symptomatic arrhythmia.
Throughout months 0–6, the research sponsor reviewed patient-marked occasions and transmissions with potential arrhythmias. A core laboratory adjudicated these probably according to the first endpoint. Lengthy-term follow-up continued for a most of 12 months. The research concluded when the final research participant had accomplished 6 months of follow-up. ILR removing at research termination was non-obligatory.
The first research goal was to estimate the proportion of HD sufferers experiencing clinically vital cardiac arrhythmias (CSAs) over 6 months. CSAs are arrhythmias thought-about almost definitely to be related to syncope and cardiac arrest or to trigger signs of hypoperfusion. They had been primarily based on commonplace definitions (69–71), suggestions of an advisory panel, and the detection capabilities of the Reveal machine and included the next:
VT≥115 BPM lasting ≥30 seconds (the speed restrict was subsequently modified to ≥130 BPM with a protocol modification).
Bradycardia with coronary heart charge ≤40 BPM for ≥6 seconds.
Asystole for ≥3 seconds.
Affected person-marked (symptomatic) occasions the place electrocardiographic evaluate confirmed an arrhythmia thought-about clinically related within the judgment of the location heart specialist.
Secondary goals had been designed to evaluate machine security, characterize cardiac rhythm and associations with dialysis or scientific occasions, and assess the flexibility of the Reveal machine to detect short-term modifications in electrocardiographic morphology and their affiliation with remedy parameters.
The next secondary goals had been specified: (1) quantifying machine and procedure-related opposed occasions; (2) recording health-related occasions, particularly dying, cardiovascular occasions, and well being care utilization; (3) analyzing the affiliation of arrhythmic occasions with health-related occasions and HD remedy parameters (this goal included CSA, different arrhythmias [e.g., AF], and parameters corresponding to coronary heart charge variability and coronary heart charge pattern); (4) quantifying atrial arrhythmia burden and analyzing associations with HD remedy parameters; and (5) assessing affiliation of captured electrocardiographic morphology and pre- and postdialysis serum electrolyte ranges.
The deliberate pattern measurement was 125 implanted sufferers. With 10% attrition this could have enabled estimation of the proportion of sufferers experiencing CSAs with a 95% confidence interval (95% CI) half-width of lower than 0.1 for any proportion. Preliminary knowledge from the primary 50 enrolled sufferers revealed CSA charges of ≥70%, which allowed estimation of 95% CI half-widths ≤0.15 with out extra enrollment. Thus, recruitment of the complete pattern measurement was not essential to reliably estimate CSA occasion charges or to find out whether or not there was a clinically related incidence of CSA within the HD inhabitants. Given the monetary and logistic challenges of recruitment and restricted potential for qualitative impact from extra enrollment, the research was capped at 66 implanted sufferers. This closing pattern measurement of 66 permits the estimation of the proportion of sufferers experiencing CSA with a 95% CI half-width of <0.13 for any proportion.
The first CSA proportion can be calculated from the cohort finishing 6-month follow-up with 95% CI bounds estimated by the Clopper–Pearson “actual” methodology utilizing the MiD-p modification (72). The evaluation can be repeated in two populations: (1) sufferers with full follow-up, plus these with incomplete knowledge who skilled CSAs, and (2) all implanted sufferers, assuming that these with incomplete follow-up and no CSAs whereas beneath remark had no occasions throughout unobserved follow-up. This can be supplemented with Kaplan–Meier survivor plots of CSA-free survival. A unfavorable binomial mannequin, acceptable for recurrent occasions and permitting for variable follow-up (73), can be used to estimate imply and 95% CI of CSA per patient-year.
Use of an invasive monitoring machine in a scientific research is an uncommon characteristic of MiD and raises distinctive points by exposing sufferers to threat in an in any other case observational research. The moral points are usually not distinctive to this design. Radiographic endpoints are regularly utilized in research, for instance, and in addition require radiation publicity with out clear profit; section 1 drug research or “first-in-human” machine research additionally expose folks to threat with out clear profit.
Given the necessity to perceive SCD and arrhythmia trigger within the dialysis inhabitants, the minimally invasive nature of ILR gadgets, and the low charge of infections when utilized in different populations, the usage of Reveal XT and LINQ in MiD was felt to be ethically acceptable. Generally, we advocate assessing “interventional-observational” analysis designs, with an moral framework that balances the significance of the data gained in opposition to potential dangers. Excessive-risk, non–minimally invasive gadgets would not often be acceptable with no potential for particular person profit. Conversely, as gadgets turn out to be smaller and fewer invasive, they might allow observational research of nonserious circumstances. Use of noninvasive instruments ought to usually be thought-about as a substitute, and investigators are obligated to fastidiously evaluate particular person threat earlier than enrolling sufferers in an observational research requiring use of an implantable monitor.
A very thorny challenge is that monitoring knowledge can alter noticed outcomes and bias estimated occasion charges. Detected arrhythmias in MiD, for instance, might mandate modifications in scientific care (e.g., pacemaker implantation, change in dialysis prescription) that modify the chance of subsequent arrhythmia, thereby lowering CSAs and leading to underestimation of the true inhabitants CSA charge.
Full disclosure to contributors and clinicians maximizes potential advantages to contributors but in addition maximizes bias. Sequestering the monitoring knowledge eliminates consequence contamination, however nondisclosure of probably dangerous and treatable circumstances found throughout analysis is ethically unacceptable.
With end-of-study batch evaluation of uncooked monitoring knowledge, outcomes and interpretation of the monitoring knowledge don’t turn out to be obtainable till after the research has concluded. That is just like storing blood samples for batch evaluation on the finish of a research. As a result of the samples (on this case monitoring info) are usually not analyzed or interpreted till after the research, this strategy eliminates the moral issues inherent to withholding analyzed knowledge; nevertheless, it imposes substantial knowledge storage necessities and will inhibit the flexibility to optimally perceive scientific options of occasions or to find out the perfect scientific response. Batch evaluation at common intervals affords a helpful intermediate strategy. Lastly, it could be potential to pick out endpoints, monitoring time frames, or knowledge disclosures so as to restrict biasing of necessary endpoints whereas permitting scientific use of analysis knowledge. In MiD, arrhythmias felt to be harmful, corresponding to asystole and sustained VT, had been reviewed in an ongoing method and shared with research sufferers and their clinicians. Conversely, disclosure of arrhythmias of unsure significance, corresponding to nonsustained VT, was not required.
Baseline Traits of the Examine Inhabitants
Sufferers had been enrolled in India (23 of 66) and the USA (43 of 66). A number of traits of the research inhabitants differed from these of the USA dialysis inhabitants (1). Imply age was decrease; solely 12.1% of sufferers had been ≥70 years of age. The next proportion of sufferers had been black (53.0%), Asian (34.8%), and male (69.7%). Diabetes was current in 63.6% of sufferers, whereas practically half of the sufferers (48.5%) had a historical past of ischemic coronary heart illness. A minority of sufferers had a historical past of arrhythmia (31.8%), and 10.6% had a historical past of AF (). Use of cardiovascular medicines was frequent, with 55%, 33%, and 48% of sufferers utilizing β-blockers, angiotensin-converting enzyme inhibitors, or angiotensin-receptor blockers or statins, respectively. Laboratory parameters () recommended enough supply of dialysis with a imply single pool Kt/V of 1.5±0.4. Potassium (5.0±1.0 mEq/L), hemoglobin (10.6 ±1.2 g/dl), and phosphorous (5.5±2.0 mg/dl) had been every mildly elevated however throughout the anticipated vary for sufferers present process long-term dialysis.
|Traits||All Sufferers (n=66)||Sufferers in United States (n=43)||Sufferers in India (n=23)||P Worth|
|Imply age at implant±SD, yr (n/N)||56.3±12.2 (66/66)||55.8±11.6 (43/43)||57.2±13.5 (23/23)||0.66|
|Male intercourse||69.7 (46/66)||62.8 (27/43)||82.6 (19/23)||0.16|
|Asian||34.8 (23/66)||0.0 (0/43)||100.0 (23/23)|
|Black||53.0 (35/66)||81.4 (35/43)||0.0 (0/23)|
|Different||1.5 (1/66)||2.3 (1/43)||0.0 (0/23)|
|White||10.6 (7/66)||16.3 (7/43)||0.0 (0/23)|
|Hispanic ethnicity||0.0 (0/66)||0.0 (0/43)||0.0 (0/23)|
|Reason for ESRD|
|Diabetes||42.4 (28/66)||34.9 (15/43)||56.5 (13/23)||0.01|
|GN||7.6 (5/66)||7.0 (3/43)||8.7 (2/23)|
|Hypertension||37.9 (25/66)||51.2 (22/43)||13.0 (3/23)|
|Different||12.1 (8/66)||7.0 (3/43)||21.7 (5/23)|
|Median ESRD classic (IQR), yr (n/N)||2.4 (1.2–5.3) (65/66)||3.5 (1.2–5.7) (42/43)||2.2 (1.1–3.0) (23/23)||<0.001|
|Prior kidney transplant||13.6 (9/66)||11.6 (5/43)||17.4 (4/23)||0.71|
|Earlier peritoneal dialysis||10.6 (7/66)||14.0 (6/43)||4.3 (1/23)||0.41|
|Present vascular entry|
|AV fistula||70.8 (46/65)||59.5 (25/42)||91.3 (21/23)||0.01|
|AV graft||24.6 (16/65)||35.7 (15/42)||4.3 (1/23)|
|Catheter||4.6 (3/65)||4.8 (2/42)||4.3 (1/23)|
|None||36.4 (24/66)||37.2 (16/43)||34.8 (8/23)|
|Sort 1||4.5 (3/66)||7.0 (3/43)||0.0 (0/23)|
|Sort 2||59.1 (39/66)||55.8 (24/43)||65.2 (15/23)|
|Imply diabetes period±SD, yr (n/N)||17.9±12.8 (37/66)||21.0±13.6 (24/43)||12.1±9.0 (13/23)||0.04|
|Hyperlipidemia||60.6 (40/66)||74.4 (32/43)||34.8 (8/23)||0.003|
|Hypertension||84.8 (56/66)||97.7 (42/43)||60.9 (14/23)||<0.001|
|Ischemic coronary heart illness||48.5 (32/66)||51.2 (22/43)||43.5 (10/23)||0.61|
|Congestive coronary heart failure||25.8 (17/66)||39.5 (17/43)||0.0 (0/23)||<0.001|
|Coronary artery bypass surgical procedure||13.6 (9/66)||11.6 (5/43)||17.4 (4/23)||0.71|
|Historical past of arrhythmia||31.8 (21/66)||48.8 (21/43)||0.0 (0/23)||<0.001|
|Atrial fibrillation||10.6 (7/66)||16.3 (7/43)||0.0 (0/23)||0.09|
|Present||7.6 (5/66)||11.6 (5/43)||0.0 (0/23)|
|By no means||69.7 (46/66)||58.1 (25/43)||91.3 (21/23)|
|Previous||22.7 (15/66)||30.2 (13/43)||8.7 (2/23)|
|Imply weight±SD, kg (n/N)||86.7±28.8 (66/66)||97.6±28.7 (43/43)||66.5±14.9 (23/23)||<0.001|
|Physique mass index ≥40 kg/m2||9.1 (6/66)||14.0 (6/43)||0.0 (0/23)||0.08|
|Imply systolic BP±SD, mmHg (n/N)||140.8±23.4 (66/66)||139.6±25.8 (43/43)||143.0±18.2 (23/23)||0.57|
|Imply diastolic BP±SD, mmHg (n/N)||76.8±12.9 (66/66)||75.5±15.1 (43/43)||79.1±6.7 (23/23)||0.18|
|Nonaspirin anticoagulants or anti platelet brokers||15 (10/66)||16 (7/43)||13 (3/23)||1.00|
|β-Blockers||55 (36/66)||58 (25/43)||48 (11/23)||0.45|
|Calcium channel blockers||59 (39/66)||51 (22/43)||74 (17/23)||0.11|
|ACEI or ARB||33 (22/66)||47 (20/43)||9 (2/23)||0.002|
|Statin||48 (32/66)||47 (20/43)||52 (12/23)||0.80|
|Aspirin||45 (30/66)||49 (21/43)||39 (9/23)||0.60|
|Laboratory Worth||All Sufferers (n)||Sufferers in United States (n)||Sufferers in India (n)||P Worth|
|BUN, (mg/dL)||59.7±17.8 (59)||58.6±15.8 (40)||62.2±21.8 (19)||0.47|
|Creatinine, mg/dl||10.0±3.4 (59)||10.9±3.5 (40)||8.3±2.4 (19)||0.01|
|Sodium, mEq/L||137.0±4.5 (59)||138.4±3.9 (40)||134.1±4.4 (19)||<0.001|
|Potassium, mEq/L||5.0±1.0 (58)||4.8±0.7 (40)||5.4±1.3 (18)||0.07|
|Calcium, mg/dl||8.7±0.8 (59)||8.8±0.8 (40)||8.4±0.8 (19)||0.08|
|Bicarbonate, mEq/L||22.2±3.7 (59)||23.8±2.9 (40)||18.8±2.9 (19)||<0.001|
|Magnesium, mg/dl||2.4±0.5 (59)||2.2±0.3 (40)||2.8±0.6 (19)||0.001|
|Phosphorous, mg/dl||5.5±2.0 (59)||5.7±2.1 (40)||5.0±1.9 (19)||0.19|
|Hemoglobin, g/dla||10.6±1.2 (56)||10.8±1.0 (38)||10.2±1.5 (18)||0.12|
|Serum albumin, g/dl||3.94±0.33 (57)||4.03±0.26 (40)||3.75±0.39 (19)||0.01|
|Parathyroid hormone, pg/ml||473.7±371.9||473.7±371.9||NA||NA|
|spKT/V||1.5±0.4 (59)||1.5±0.3 (40)||1.4±0.6 (19)||0.44|
A number of traits differed considerably between United States and Indian sufferers. Particularly, Indian sufferers weighed much less (66.5 versus 97.6 kg), had been extra more likely to have diabetic kidney illness (56.5% versus 34.9%), had been extra more likely to dialyze by way of an arteriovenous fistula (91.3% versus 59.5%), had a shorter dialysis classic (2.2 versus 3.5 years), and had been much less more likely to have hypertension (60.9% versus 97.7%) than contributors in the USA. Laboratory traits had been usually related, however bicarbonate (18.8 versus 23.8 mEq/L) and sodium (134.1 versus 138.4 mEq/L) concentrations had been decrease in India.
This regional variation and elevated variability in laboratory and scientific traits current challenges and alternatives. Evaluation of country-specific arrhythmia charges is necessary, however the wide selection of traits, corresponding to physique mass index, hypertension, and bicarbonate concentrations, might present a larger potential to research associations of those elements with arrhythmia than would have been potential had the research recruited solely inside the USA. World enrollment ought to thus restrict the impact of country-specific dialysis practices on our findings and will improve relevance to the worldwide HD inhabitants whereas requiring extra cautious extrapolation to the USA inhabitants.
MiD as a Paradigm
The MiD research illustrates the potential of invasive monitoring to enhance understanding of the pathophysiology of ESRD and elucidate the true nature or reason for scientific occasions in dialysis sufferers. From our expertise, it appears clear that when investigators are engaged, dangers are moderately low, analysis questions are necessary, and scientific profit is feasible, dialysis sufferers might be engaged and their collaboration secured in observational research utilizing invasive monitoring procedures.
Future analysis on ILR know-how in ESRD ought to embody research to find out the affiliation between subclinical AF and the chance of stroke, long-term research with adequate pattern measurement to seize terminal cardiac rhythms on the time of SCD, and interventional research testing the impact of individualization of the dialysis prescription on arrhythmia. Gadgets with miniaturized impedance know-how will facilitate learning associations of quantity standing with arrhythmia and extra subtle investigations into hyperlinks between ultrafiltration charge, BP, quantity standing, cardiovascular dying, and intradialytic hypotension. Outdoors of the cardiovascular enviornment, implantable glucose screens stand out as a know-how that might be readily used to definitively decide the true relationship between serum glucose ranges and hemoglobin A1c or scientific outcomes in ESRD (74). Equally, one can envision utilizing stress or move monitoring gadgets to higher perceive entry physiology and trajectories of entry maturation and failure.
Understanding the causal sequence of occasions within the pathway to dying is important to figuring out alternatives for prolonging life in ESRD. Regardless of advances in renal care, the interval from the final scientific evaluation till out-of-hospital dying stays ripe for investigation (75–78). In individuals present process in-center HD, common well being care contact limits the time throughout which no very important info is recorded; nevertheless, out-of-center SCD stays frequent, with little details about the hours and days main as much as the ultimate minutes of life. Data on these intervals in home-care sufferers is extra restricted with respect to cardiac rhythm and very important standing (79).
Typical cardiac pacemakers have diminished the mortality related to bradycardia and permit bradycardic sufferers to have regular actuarial survival in contrast with age- and sex-matched cohorts (80). In these with accepted indications for implantable cardioverter-defibrillators (ICDs), the speed of acceptable remedy for deadly rhythms is roughly 20% over the lifetime of the implant (80), and first and secondary prevention of SCD with ICDs in sufferers with left ventricular dysfunction improves survival of those teams. In a subset of sufferers with left ventricular dysfunction who’ve ventricular dyssynchrony (e.g., extended left bundle-branch block morphology QRS advanced on electrocardiography), the addition of a left ventricular lead and biventricular pacing improves survival from each sudden and pump failure dying (82).
Nonetheless, the precise translation of those therapies to sufferers with superior CKD and ESRD is proscribed, as famous above, by an absence of information that enable inferences on their potential dangers and advantages. ICDs, for instance, face increased defibrillation thresholds which will inhibit profitable cardioversion of VT/fibrillation in sufferers with ESRD (83). This may occasionally replicate larger levels of total left ventricular fibrosis and hypertrophy in contrast with these with out years of CKD. There may be additionally restricted details about the necessity for backup bradycardia pacing in sufferers with ESRD who’ve ICDs implanted but might have a scientific occasion the place bradycardia is the complicating rhythm. Lastly, and most critically, the proportion of dying that’s really avoidable with machine remedy versus how a lot is actually attributable to pump failure or noncardiac major causes that can not be influenced by any type of machine remedy stays unknown.
The MiD research is uniquely designed to realize important insights into sufferers each within the clinic and hospital and, extra necessary, locally and households through which they stay. Recording the newest baseline rhythm, important triggers (untimely depolarizations, pauses), pathologic intermediate rhythms (monomorphic, polymorphic VT), and terminal patterns (coronary heart block, VT, VF, systole, and different types of pulseless electrical exercise) will present essential knowledge permitting investigators to start piecing collectively the sequence of occasions and proximate causes of the final minutes of life in ESRD. Equally, identification of scientific, demographic, or electrophysiologic variables related to the ultimate electrical sequence might show helpful for predicting deadly, but treatable, rhythms, for the potential utility of and figuring out these almost definitely to profit from ICD insertion, for figuring out whether or not back-up pacing capabilities are wanted, or for figuring out whether or not sufferers would profit from withdrawal of nodal blockade (e.g., β-blockers).
By capturing the complete constellation of cardiac rhythm throughout a protracted interval, the MiD research will present info on the extent to which beforehand undetected AF or different tachyarrhythmias and bradyarrhythmias contribute to morbidity in ESRD. Lastly, as famous beforehand, the detailed seize of scientific knowledge in MiD is important for correlating captured rhythms with concurrent scientific signs to keep away from complicated “agonal” rhythms that seem secondary to another life-ending occasion, corresponding to sepsis or stroke (for which software of cardiac pacing gadgets will not be acceptable), with major arrhythmia as a reason for dying.
Evaluation of blood chemistries and knowledge on the dialysis prescription from MiD might alternatively determine prescription traits or electrolyte ranges strongly related to the prevalence of arrhythmia. Thus, the ultimate outcomes might counsel methods to tailor the dialysis prescription so as to restrict arrhythmia. On this regard, associations between blood-dialysate potassium or calcium gradients and arrhythmia prevalence in MiD are eagerly anticipated.
Sooner or later, notably as point-of-care info turns into obtainable, long-term monitoring might enable nephrologists to change the dialysis prescription in response to minute-by-minute modifications in electrocardiographic morphology or the peridialytic prevalence of arrhythmia. Lengthy-term monitoring would possibly enable the identification of sufferers with subclinical AF more likely to profit from anticoagulation. ILR research may facilitate dedication of whether or not sure dialysate-serum electrolyte gradients are related to a better probability of arrhythmia and must be prevented. Lastly, scientific trials evaluating outcomes following randomization to an ILR with detection of and response to arrhythmia versus routine commonplace of care could also be thought-about to find out whether or not the potential of those gadgets can cut back mortality within the dialysis inhabitants.
In abstract, we imagine that leveraging trendy cardiac rhythm monitoring in individuals with ESRD supplies an necessary alternative to advance the science of cardiorenal medication. We await the outcomes contributed by devoted and altruistic sufferers, households, and investigators who’re finishing up the protocol on the time of this writing.
All the authors obtained analysis assist and/or consulting charges from Medtronic (Minneapolis, MN) in relationship to the design of the research. D.M.C. obtained consulting from Questcor Prescribed drugs (Anaheim, CA), professional witness charges associated to dialysate composition from Fresenius Medical Care (Waltham, MA), and charges associated to service on scientific occasions committee from PLC Medical Programs (Milford, MA). J.D.R. obtained audio system bureau, marketing consultant, and analysis assist from Medtronic; audio system bureau and analysis assist from St Jude Medical (St. Paul, MN); and audio system bureau from Biotronik (Berlin, Germany). C.A.H. obtained analysis assist from Zoll (Chelmsford, MA) and inventory/fairness curiosity from Cambridge Coronary heart, Boston Scientific (Tewksbury, MA).
The authors want to acknowledge the assist and suggestions from the research group at Medtronic together with John Burnes and Amy Roettger.
The MiD research was funded by Medtronic and designed by Medtronic in collaboration with an advisory committee that included the authors.
The MiD investigators and committees are listed within the Supplemental Materials.
353: 238–248, 2005 [PubMed] [Google Scholar]
65: 2380–2389, 2004 [PubMed] [Google Scholar]
3: e001363, 2014 [PMC free article] [PubMed] [Google Scholar]
80: 572–586, 2011 [PubMed] [Google Scholar]
65: S1–S140, 2015 [PubMed] [Google Scholar]
58: 599–607, 2011 [PubMed] [Google Scholar]
74: 1335–1342, 2008 [PubMed] [Google Scholar]
26: 2815–2820, 2015 [PMC free article] [PubMed] [Google Scholar]
7: e48578, 2012 [PMC free article] [PubMed] [Google Scholar]
2: 305–309, 1988 [PubMed] [Google Scholar]
339: 212–213, 1992 [PubMed] [Google Scholar]
19: 247–257, 2014 [PMC free article] [PubMed] [Google Scholar]
65: 1263–1265, 2015 [PubMed] [Google Scholar]
12: 2047–2055, 2015 [PubMed] [Google Scholar]
60: 350–357, 2001 [PubMed] [Google Scholar]
79: 218–227, 2011 [PubMed] [Google Scholar]
8: 797–803, 2013 [PMC free article] [PubMed] [Google Scholar]
85: 174–181, 2014 [PubMed] [Google Scholar]
365: 1099–1107, 2011 [PubMed] [Google Scholar]
55: 1553–1559, 1999 [PubMed] [Google Scholar]
88: 569–575, 2015 [PubMed] [Google Scholar]
81: 1108–1115, 2012 [PMC free article] [PubMed] [Google Scholar]
2: 216–223, 2000 [PubMed] [Google Scholar]
345: 1473–1482, 2001 [PubMed] [Google Scholar]
21: 300–307, 2008 [PubMed] [Google Scholar]
336: 1629–1633, 1997 [PubMed] [Google Scholar]
105: 1354–1359, 2002 [PubMed] [Google Scholar]
11: 36–41, 2006 [PubMed] [Google Scholar]
5: 805–813, 2010 [PMC free article] [PubMed] [Google Scholar]
5: 39–44, 1990 [PubMed] [Google Scholar]
9: 1018–1022, 1998 [PubMed] [Google Scholar]
3: 19–26, 2008 [PMC free article] [PubMed] [Google Scholar]
176: 99–109, 2014 [PMC free article] [PubMed] [Google Scholar]
18: 1525–1533, 2007 [PubMed] [Google Scholar]
72: 977–984, 2007 [PubMed] [Google Scholar]
194: 45–55, 2008 [PubMed] [Google Scholar]
121: 4393–4408, 2011 [PMC free article] [PubMed] [Google Scholar]
84 Suppl 1: i18–19:dialogue i50, 2000 [PMC free article] [PubMed] [Google Scholar]
47: 488–495, 2006 [PubMed] [Google Scholar]
121: 188–192, 2010 [PMC free article] [PubMed] [Google Scholar]
14: 195–203, 2005 [PubMed] [Google Scholar]
126: 2293–2301, 2012 [PMC free article] [PubMed] [Google Scholar]
22: 349–357, 2011 [PMC free article] [PubMed] [Google Scholar]
27: 3816–3822, 2012 [PubMed] [Google Scholar]
37: 622–630, 2013 [PubMed] [Google Scholar]
88: 2618–2622, 1993 [PubMed] [Google Scholar]
83: 162–169, 1991 [PubMed] [Google Scholar]
112: c171–c176, 2009 [PubMed] [Google Scholar]
76: 612–617, 2012 [PubMed] [Google Scholar]
17: 1634–1638, 2002 [PubMed] [Google Scholar]
21: 425–430, 2006 [PubMed] [Google Scholar]
100: 685–690, 2014 [PubMed] [Google Scholar]
22: 983–988, 1991 [PubMed] [Google Scholar]
23: 112–118, 2013 [PMC free article] [PubMed] [Google Scholar]
35: 491–497, 2012 [PubMed] [Google Scholar]
54: 680–692, 2009 [PubMed] [Google Scholar]
31: 36–43, 2015 [PubMed] [Google Scholar]
107: 1614–1619, 2003 [PubMed] [Google Scholar]
366: 120–129, 2012 [PubMed] [Google Scholar]
114: 869–874, 2014 [PubMed] [Google Scholar]
7: 1223–1229, 2014 [PubMed] [Google Scholar]
370: 2478–2486, 2014 [PubMed] [Google Scholar]
122: 1629–1636, 2010 [PubMed] [Google Scholar]
371: 1260, 2014 [PubMed] [Google Scholar]
324: 781–788, 1991 [PubMed] [Google Scholar]
17: 857–872, 1998 [PubMed] [Google Scholar]
70: 1503–1509, 2006 [PubMed] [Google Scholar]
11: 261–273, 2004 [PubMed] [Google Scholar]
4: 125–130, 2003 [PubMed] [Google Scholar]
11: 294–303, 2004 [PubMed] [Google Scholar]
4: 159–162, 2009 [PubMed] [Google Scholar]
24: 405–415, 2011 [PubMed] [Google Scholar]
11: 305–316, 2002 [PubMed] [Google Scholar]
116: 2020–2040, 2015 [PubMed] [Google Scholar]
11: 199–204, 2004 [PubMed] [Google Scholar]