Pharmacologic therapy for engraftment arrhythmia induced by transplantation of human cardiomyocytes

Abstract

Heart failure remains a significant cause of morbidity and mortality following myocardial infarction. Cardiac remuscularization with transplantation of human pluripotent stem cell-derived cardiomyocytes is a promising preclinical therapy to restore function. Recent large animal data, however, have revealed a significant risk of engraftment arrhythmia (EA). Although transient, the risk posed by EA presents a barrier to clinical translation. We hypothesized that clinically approved antiarrhythmic drugs can prevent EA-related mortality as well as suppress tachycardia and arrhythmia burden. This study uses a porcine model to provide proof-of-concept evidence that a combination of amiodarone and ivabradine can effectively suppress EA. None of the nine treated subjects experienced the primary endpoint of cardiac death, unstable EA, or heart failure compared with five out of eight (62.5%) in the control cohort (hazard ratio = 0.00; 95% confidence interval: 0-0.297; p = 0.002). Pharmacologic treatment of EA may be a viable strategy to improve safety and allow further clinical development of cardiac remuscularization therapy.

Keywords: antiarrhythmic drugs; cardiac cell therapy; cardiac regeneration; cardiac remuscularization; electrophysiology; embryonic stem cells; engraftment arrhythmia; heart failure; myocardial infarction; sudden cardiac death.

Figure 1

Flowchart of the study design Phase 1 consisted of nine total subjects, four untreated with any antiarrhythmic to study the natural history of EA and five used to screen seven candidate antiarrhythmic agents. Amiodarone and ivabradine were found to have promising signals of effect and advanced for further study. Phase 2 consisted of 19 total subjects: 9 treated with amiodarone and ivabradine and 8 untreated following hESC-CM transplantation, and 2 untreated following sham transplantation.

Figure 2

Variable morphologies of EA in a single minipig Examples of normal sinus rhythm (NSR) and three morphologies of EA resembling accelerated junctional rhythm (AJR), ventricular tachycardia (VT), and accelerated idioventricular rhythm (AIVR) were observed in a single untreated subject (12). Note the variation in rate, electrical axis, and QRS duration. A continuous rhythm recording below exhibits polymorphic EA with QRS complexes varying in rate, duration, and electrical axis. No sustained arrythmias were noted in the sham transplant controls. One box vertical 200 mV, horizontal 0.2 s.

Figure 3

Acute effects of amiodarone and ivabradine on engraftment arrhythmia Amiodarone was effective as an intravenous bolus to cardiovert engraftment arrythmia to normal sinus or a lower heart rate transiently in three separate instances (A) (red line). Ivabradine administered orally significantly slowed EA but did not cardiovert 2 days following initiation (B). These data supported a combined amiodarone and ivabradine antiarrhythmic strategy for rhythm and rate control of EA. One box vertical 200 mV, horizontal 0.2 s.

Figure 4

Antiarrhythmic treatment with amiodarone and ivabradine for engraftment arrhythmia in pig (A) Kaplan-Meier curve for freedom from primary outcome of cardiac death, unstable EA or heart failure was significantly improved in the treated (n = 9) compared with the untreated cohort (n = 8, p = 0.002). Tic marks on the treatment line indicate non-cardiac death due to opportunistic infection (days 19 and 26) or a planned euthanasia (day 30). (B) The Kaplan-Meier curve for overall survival shows statistically borderline improvement in the treated compared with the untreated cohort (p = 0.051). Each subject is an independent experiment. ^∗Death due to Pneumocystis pneumonia. ^∗∗Death due to porcine cytomegalovirus. CI, 95% confidence interval; No., number.

Figure 5

Effect of antiarrhythmic treatment on heart rate and arrhythmia burden Pooled daily average heart rate (A) and pooled daily average arrhythmia burden (B) in treated (n = 9, blue) compared with untreated (n = 8, red) cohorts. The difference in heart rate or arrhythmia burden between treated and untreated cohorts was not significant (NS) by day 30 post-transplantation. Sham transplant (n = 2, gray) did not induce tachycardia or arrythmia. Data are represented as mean ± SEM and each subject is an independent experiment. Subject-level averaged daily heart rate (C) and arrhythmia burden (D) for antiarrhythmic treated (blue), untreated (red), and sham transplant (gray). Unexpected death or euthanasia are denoted by black symbols. Overall peak and mean daily heart rate (E) and overall peak and mean daily arrythmia burden (F) were significantly reduced in treated (blue) compared with untreated (red) cohorts. No tachycardia or arrhythmias were noted in the sham transplant control cohort. ^∗p ≤ 0.05, ^∗∗p ≤ 0.01.

Figure 6

Transplanted hESC-CM grafts interact with a diffuse Purkinje conduction system in the porcine myocardium An hPSC-cardiomyocyte graft 2 weeks post-transplantation, marked by human-specific slow skeletal cardiac troponin I (ssTnI) (red) (Bedada et al., 2014), interacts with Cx40-positive (white) Purkinje fibers. Wheat germ agglutinin (WGA) (green) delineates cardiac sarcolemma. Purkinje-transitional cell-graft (left panel) and direct Purkinje-graft (right panel) interactions are observed. Sale bars, 100 or 20 μm (magnified).