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Background Although amiodarone is one of the most effective pharmacologic agents used in clinical management of atrial fibrillation (AF), little is know about its differential effects in atrial and ventricular myocardium. Objectives To compare the electrophysiological effects of chronic amiodarone in atria and ventricles. Methods We compared the electrophysiological characteristics of coronary-perfused atrial and ventricular wedge preparations isolated from untreated and chronic amiodarone-treated dogs (Amiodarone, 40 mg/kg/day for 6 weeks, n=12). Results Chronic amiodarone prolonged action potential duration (APD90) predominantly in atria compared to ventricles and prolonged the effective refractory period (ERP) more than APD90 in both ventricular and atrial preparations (particularly in the latter), due to the development of post-repolarization refractoriness. Amiodarone reduced dispersion of APD90 in both atria and ventricles. Although maximum rate of rise of the action potential upstroke (Vmax) was significantly lower in both atria and ventricles of amiodarone-treated hearts vs. untreated controls, the reduction of Vmax was much more pronounced in atria. Amiodarone prolonged P wave duration more significantly than QRS duration, reflecting greater slowing of conduction in atria vs. ventricles. These atrioventricular distinctions were significantly accentuated at faster activation rates. Persistent acetylcholine-mediated AF could be induced in only 1/6 atria from amiodarone-treated vs. 10/10 untreated dogs. Conclusions Our results indicate that, under the conditions studied, chronic amiodarone has potent atrial-predominant effects to depress sodium channel-mediated parameters and that this action of the drug is greatly potentiated by its ability to prolong APD predominantly in the atria, thus contributing to its effectiveness to suppress AF.

Abstract-The trifascicular nature of the intraventricular conduction system and the concept of trifascicular block and hemiblock were described by Rosenbaum and his coworkers in 1968. Since then, anatomic, pathological, electrophysiological, and clinical studies have confirmed the original description and scarce advances have been developed on the subject. In the present study, we attempt to review and redefine reliable criteria for the electrocardiographic and vectorcardiographic diagnosis of left anterior and posterior hemiblock. One of the most important problems related to hemiblocks is that they may simulate or conceal the electrocardiographic signs of myocardial infarction or myocardial ischemia and may mask or simulate ventricular hypertrophy. Illustrative examples of these associations are shown to help the interpretation of electrocardiograms. The incidence and prevalence of the hemiblocks is presented based on studies performed in hospital patients and general populations. One of the most common causes of hemiblocks is coronary artery disease, and there is a particularly frequent association between anteroseptal myocardial infarction and left anterior hemiblock. The second most important cause is arterial hypertension, followed by cardiomyopathies and Lev and Lenègre diseases. The hemiblocks may also occur in aortic heart disease and congenital cardiopathies. Left anterior hemiblock is more common in men and increases in frequency with advancing age. Evidence is presented regarding the relationship of spontaneous closure of ventricular septal defects, which may explain the finding of this and other conduction defects in young populations. Isolated left anterior hemiblock is a relatively frequent finding in subjects devoid of evidence of structural heart disease. Conversely, isolated left posterior hemiblock is a very rare finding; its prognostic significance is unknown and is commonly associated with right bundle-branch block. The most remarkable feature of this association is that the prognosis is much more serious with a great propensity to develop complete atrioventricular block and Adams-Stoke seizures. Key Words: epidemiology Ⅲ heart septal defects Ⅲ myocardial infarction Ⅲ heart block Ⅲ bundle-branch block T hirty-eight years have elapsed since Rosenbaum et al published their seminal work that put together diverse previous observations and brought about a rational and complete analytic approach to the trifascicular concept of intraventricular conduction.These conclusive studies and an exhaustive review of the preceding knowledge of the subject were first published in the Spanish monograph, 1 and later a shorter updated version was presented to acquaint the English reader with the electrocardiographic manifestations and clinical correlation of the abnormal spread of ventricular excitation. 2 A series of articles published by the same authors between 1969 and 1973 also contributed to the expansion of the recognition of this research work. As stated by Herman N. Uhley, 3 this work triggered and infl...

To the best of our knowledge, this is the first study in which SR-Ca2+ transients are recorded in the intact heart, revealing a previously unknown participation of SR on cytosolic Ca2+ overload upon reperfusion in the intact beating heart. Additionally, the associated shortening of phase 2 of the AP may provide a clue to explain early reperfusion arrhythmias.

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