Triggered activity as arrhythmogenic mechanism after myocardial infarction: clinical and electrophysiologic study of one case

Mechanism of Ventricular Tachycardia Occurring in Chronic Myocardial Infarction Scar

Cardiac arrest is the leading cause of death in the more economically developed countries. Ventricular tachycardia associated with myocardial infarct is a prominent cause of cardiac arrest. Ventricular arrhythmias occur in 3 phases of infarction: during the ischemic event, during the healing phase, and after the scar matures. Mechanisms of arrhythmias in these phases are distinct. This review focuses on arrhythmia mechanisms for ventricular tachycardia in mature myocardial scar. Available data have shown that postinfarct ventricular tachycardia is a reentrant arrhythmia occurring in circuits found in the surviving myocardial strands that traverse the scar. Electrical conduction follows a zigzag course through that area. Conduction velocity is impaired by decreased gap junction density and impaired myocyte excitability. Enhanced sympathetic tone decreases action potential duration and increases sarcoplasmic reticular calcium leak and triggered activity. These elements of the ventricular tachycardia mechanism are found diffusely throughout scar. A distinct myocyte repolarization pattern is unique to the ventricular tachycardia circuit, setting up conditions for classical reentry. Our understanding of ventricular tachycardia mechanisms continues to evolve as new data become available. The ultimate use of this information would be the development of novel diagnostics and therapeutics to reliably identify at-risk patients and prevent their ventricular arrhythmias.

Beta adrenergic blockade in the treatment of sustained ventricular tachycardia or ventricular fibrillation

The value of beta-blockers as antiarrhythmic drugs in patients with sustained VT or VF has received only little attention. This article summarizes the current state of knowledge regarding the identification of patients with sustained VT or VF with the highest benefit of beta-blockade. The antiarrhythmic mechanisms of beta-blockade and its efficacy as single or adjuvant therapy in patients with sustained VT or VF are reviewed. Current insights into the effects of beta-blockade in patients suffering from VT, in particular in the setting of heart failure, are discussed and future directions are considered.