Ventricular tachycardia in healing canine myocardial infarction: evidence for multiple reentrant mechanisms

Sudden adult death

In the investigation of sudden death in adults, channelopathies, such as long QT syndrome, have risen to the fore in the minds of forensic pathologists in recent years. Examples of these disorders are touched upon in this review as an absence of abnormal findings at postmortem examination is characteristic and the importance of considering the diagnosis lies in the heritable nature of these conditions. Typically, a diagnosis of a possible channelopathy is evoked as an explanation for a 'negative autopsy' in a case of apparent sudden natural death. However, the one potential adverse effect of this approach is that subtle causes of sudden death may be overlooked. The intention of this article is to review and discuss potential causes of sudden adult death (mostly natural) that should be considered before resorting to a diagnosis of possible channelopathy. Nonetheless, it becomes apparent that many of the potential causes of sudden death can have a genetic basis. Thus, it becomes an important consideration that there may be a genetic basis to sudden death that extends beyond the negative autopsy.

Electrophysiologic Actions of d,l-Sotalol and GLG-V-13 in Ischemically Injured Canine Epicardium

The electrophysiologic actions of the class III antiarrhythmic agents, GLG-V-13 and d,l-sotalol, were examined in superfused normal and ischemically injured epicardium. Both drugs produced concentration and reverse-use dependent prolongation of the action potential duration in normal myocardium without altering resting potential, action potential amplitude, or Vmax. Both drugs increased the slope of restitution curves in normal epicardium but prevented action potential alternans at short cycle lengths. The response of superfused ischemically injured left ventricular epicardium to drug 4 days after coronary artery ligation was determined by the extent of ischemic injury, with no electrophysiologic changes produced within epicardial cells characterized by prominent action potential shortening and no further action potential shortening with pacing. Cells demonstrating less severe injury (as evidenced by less severely depressed action potential amplitudes, Vmax, and action potential durations) retained a limited ability to respond to drug administration with action potential prolongation. A concentration-dependent, increased disparity of action potential duration was observed concurrent with the ability of single premature stimuli to induce monomorphic tachycardia. The present data demonstrate a variable response of ischemically injured canine epicardial cells to action potential prolongation with GLG-V-13 and d,l-sotalol, facilitating localized reentry in vitro, despite a failure of the same drugs to facilitate reentrant tachycardia in vivo.

Characterization and incidence of inducible monomorphic ventricular tachycardia in a postinfarction rabbit model

OBJECTIVE

Ventricular tachycardia (VT), occurring late after myocardial infarction, is an important cause of sudden death. Animal models are useful for the investigation of this arrhythmia. The aim of this study is to develop and characterize a model of late postinfarction monomorphic VT in the rabbit.

METHODS AND RESULTS

Myocardial infarction was created by ligation of the left circumflex artery. Cardiac electrophysiologic studies were performed 10 to 17 days postinfarction in 39 rabbits, in 10 sham-operated rabbits, and 6 control rabbits. Ventricular tachycardia was defined as a broad-complex tachycardia with a cycle length of more than 100 milliseconds, a duration of more than 10 seconds, and monomorphic QRS complexes. Using programmed stimulation, we induced VT in 9 rabbits (23%) in the infarct group but in none of the sham or control animals. The mean infarct size was 23% +/- 9% (mean +/- SD) of the left ventricle.

CONCLUSION

Coronary ligation in the rabbit creates a substrate, which allows the induction of sustained monomorphic VT with programmed stimulation. Monomorphic VT is not inducible in rabbits without myocardial infarction. This model might allow the testing of interventions that reduce the incidence of VT late after myocardial infarction.

Cardiac-specific loss of N-cadherin leads to alteration in connexins with conduction slowing and arrhythmogenesis

The remodeling of ventricular gap junctions, as defined by changes in size, distribution, or function, is a prominent feature of diseased myocardium. However, the regulation of assembly and maintenance of gap junctions remains poorly understood. To investigate N-cadherin function in the adult myocardium, we used a floxed N-cadherin gene in conjunction with a cardiac-specific tamoxifen-inducible Cre transgene. The mutant animals appeared active and healthy until their sudden death approximately 2 months after deleting N-cadherin from the heart. Electrophysiologic analysis revealed abnormal conduction in the ventricles of mutant animals, including diminished QRS complex amplitude consistent with loss of electrical coupling in the myocardium. A significant decrease in the gap junction proteins, connexin-43 and connexin-40, was observed in N-cadherin-depleted myocytes. Perturbation of connexin function resulted in decreased ventricular conduction velocity, as determined by optical mapping. Our data suggest that perturbation of the N-cadherin/catenin complex in heart disease may be an underlying cause, leading to the establishment of the arrythmogenic substrate by destabilizing gap junctions at the cell surface.