Thus, there are now several chronic canine myocardial infarction ventricular tachyarrhythmia models which are available for the evaluation of new antiarrhythmic drugs (Table I). The available models fulfill many, but not all of the requirements for an ideal chronic arrhythmia model (Table 11). The sustained arrhythmias initiated in these models using programmed pacing presumably have the same localized reentrant mechanism that characterizes chronic human myocardial infarction and chronic coronary 26 artery disease. However, these models are not suitable for determining whether a new drug will abolish spontaneous ly-occurring PVCs. In addition, these models are of unproven value in the study of acute spontaneously occurring sudden death; although recently initiated, provocative work may shed further light on this subject. Most importantly, the available models do seem well-suited to the evaluation of new drugs intended for use in chronic coronary artery disease patients at risk for sustained reentrant ventricular tachycardia or VF. Notably, the results of preliminary electropharmacologic studies in these canine models parallel closely those findings reported in human patients with sustained life-threatening ventricu lar tachyarrhythmias (Table Ill). Therefore, increased use of these chronic models for new antiarrhythmic drug testing is strongly recommended. TABLE II Ideal vs Available Chronic Canine - Arrhythmia Models Ideal Available 1. (a) Arrhythmia mechanism comparable to Yes patients with chronic CAD: Reentry (b) Pathophysiology similar (e. g., atherogenic CAD) No 2. Susceptible to: (a) spontaneous PVCs No l No (b) spontaneous VT/VF (c) inducible VT/VF Yes 3."

During the past decade enormous progress has been made in the development of new cardiovascular drugs and in our understanding of the clinical pharma cology and the pharmacokinetics of old drugs. In addition, newer applications of older agents have emerged. For example, vasodilators such as nitroglycerin are now being employed in the treatment of congestive heart failure, and anti hypertensives such as bretylium are used in the management of ventricular arrhythmias. Individual chapters in this book focus on (1) the clinical pharmacology and pharmacokinetics of the individual drugs, and (2) the clinical applications of these drugs, with attention also to serum concentrations, pathophysiology, and drug interactions where appropriate. The contributors to this text have labored to provide the reader with a meaningful, practical update on the clinical uses and usefulness of cardioactive drugs. We are deeply grateful to each of them for their generous participation in this endeavor. LEONARD S. DREIFUS, M.D. ALBERT N. BREST, M.D. 1. ANTIARRHYTHMIC AGENTS LEONARD S. DREIFUS and JOEL MORGANROTH Ideally, the management of cardiac arrhythmias must be predicated on (1) complete elucidation of the genesis of the various rhythm disturbances, and (2) a full understanding of the pharmacologic action of individual antiarrhythmic agents. Only with this precise information does it become possible to administer a particular agent or agents specifically effective against a given arrhythmia."