BACKGROUND Sympathetic activation in ischemic heart disease can cause lethal arrhythmias. These often are preceded by premature ventricular complexes (PVCs), which at the cellular level could result from delayed afterdepolarizations.OBJECTIVE The purpose of this study was to identify and map vulnerable areas for arrhythmia initiation after myocardial infarction (MI) and to explore the link between PVCs and cellular events.METHODS Anterior-septal wall MI was induced by 120 minutes of coronary occlusion followed by reperfusion (27 MI and 16 sham pigs). After 4 weeks, EnSiteÔ electroanatomic mapping combined with imaging was performed to precisely locate PVC sites of origin and subsequently record monophasic action potentials. Cardiomyocytes were isolated from different regions to study regional cellular remodeling. Isoproterenol was used as a surrogate for adrenergic stimulation both in vivo and in cardiomyocytes.RESULTS PVCs originated from the MI border zone (BZ) and occurred at discrete areas with clusters of PVCs within the BZ. At these sites, frequent delayed afterdepolarizations and occasional associated spontaneous action potentials translating to a PVC were present. Cardiomyocytes isolated from the MI BZ exhibited more spontaneous action potentials than cardiomyocytes from remote regions. Sensitivity to adrenergic stimulation was increased in MI, in vivo and in cardiomyocytes. In awake, freely moving MI animals, frequent PVCs, ventricular arrhythmia, and sudden cardiac death occurred spontaneously at moderately elevated heart rates.CONCLUSION Post-MI, arrhythmias initiate from discrete vulnerable areas within the BZ, where delayed afterdepolarizations, related to increased adrenergic response of BZ cardiomyocytes, can generate PVCs.

Ischemic heart disease is the most common cause of lethal ventricular arrhythmias and sudden cardiac death (SCD). In patients who are at high risk after myocardial infarction, implantable cardioverter defibrillators are the most effective treatment to reduce incidence of SCD and ablation therapy can be effective for ventricular arrhythmias with identifiable culprit lesions. Yet, these approaches are not always successful and come with a considerable cost, while pharmacological management is often poor and ineffective, and occasionally proarrhythmic. Advances in mechanistic insights of arrhythmias and technological innovation have led to improved interventional approaches that are being evaluated clinically, yet pharmacological advancement has remained behind. We review the mechanistic basis for current management and provide a perspective for gaining new insights that centre on the complex tissue architecture of the arrhythmogenic infarct and border zone with surviving cardiac myocytes as the source of triggers and central players in re-entry circuits. Identification of the arrhythmia critical sites and characterisation of the molecular signature unique to these sites can open avenues for targeted therapy and reduce off-target effects that have hampered systemic pharmacotherapy. Such advances are in line with precision medicine and a patient-tailored therapy.

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BACKGROUND: After myocardial infarction, the infarct border zone (BZ) is the dominant source of life-threatening arrhythmias, where fibrosis and abnormal repolarization create a substrate for reentry. We examined whether repolarization abnormalities are heterogeneous within the BZ in vivo and could be related to heterogeneous cardiomyocyte remodeling. METHODS: Myocardial infarction was induced in domestic pigs by 120-minute ischemia-reperfusion injury. After 1 month, remodeling was assessed by magnetic resonance imaging, and electroanatomical mapping was performed to determine the spatial distribution of activation-recovery intervals. Cardiomyocytes were isolated and tissue samples collected from the BZ and remote regions. Optical recording allowed assessment of action potential duration (di-8-Anepps, stimulation at 1 Hz, 37 °C) of large cardiomyocyte populations while gene expression in cardiomyocytes was determined by single nuclear RNA sequencing. RESULTS: In vivo, activation-recovery intervals in the BZ tended to be longer than in remote with increased spatial heterogeneity evidenced by a greater local SD (3.5±1.3 ms versus remote: 2.0±0.5 ms, P =0.036, n pigs =5). Increased activation-recovery interval heterogeneity correlated with enhanced arrhythmia susceptibility. Cellular population studies (n cells =635–862 cells per region) demonstrated greater heterogeneity of action potential duration in the BZ (SD, 105.9±17.0 ms versus remote: 73.9±8.6 ms; P =0.001; n pigs =6), which correlated with heterogeneity of activation-recovery interval in vivo. Cell-cell gene expression heterogeneity in the BZ was evidenced by increased Euclidean distances between nuclei of the BZ (12.1 [9.2–15.0] versus 10.6 [7.5–11.6] in remote; P <0.0001). Differentially expressed genes characterizing BZ cardiomyocyte remodeling included hypertrophy-related and ion channel–related genes with high cell-cell variability of expression. These gene expression changes were driven by stress-responsive TFs (transcription factors). In addition, heterogeneity of left ventricular wall thickness was greater in the BZ than in remote. CONCLUSIONS: Heterogeneous cardiomyocyte remodeling in the BZ is driven by uniquely altered gene expression, related to heterogeneity in the local microenvironment, and translates to heterogeneous repolarization and arrhythmia vulnerability in vivo.

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