Tachycardia-dependent and bradycardia-dependent intraventricular conduction defects in acute myocardial infarction: electrocardiographic, electrophysiologic, and clinical correlates

Pharmacological stress testing of the His-Purkinje system in patients with bifascicular block

This literature review, based mainly on the English-language literature, focuses on pharmacological stress testing of the His-Purkinje system as part of an invasive electrophysiological study. The main target group for this investigation is patients with bifascicular block and syncope in which intermittent high grade AV block is suspected. Several drugs have been used for this purpose, mainly Class I antiarrhythmic agents such as ajmaline, procainamide, disopyramide, and flecainide. Most studies, unfortunately, suffer from limited patient numbers, lack of adequate control groups, and/or adequate follow-up. The sensitivity of the disopyramide stress test has been shown to be 75%-100% for prediction of impending high grade AV block. The specificity was > 90%. Studies on procainamide have shown a sensitivity of 60% but the specificity has not been assessed. There are no studies allowing a strict comparison of the diagnostic value of pharmacological provocation with different drugs. Based on the similarities of the electrophysiological effects on the His-Purkinje system of the above Class I agents, it is reasonable to assume that all of them might be of diagnostic value in the present clinical context, provided atrial and ventricular stimulation after drug is included in the protocol.

Co-existing tachycardia and bradycardia dependent incomplete and complete right bundle branch block: evidence for diffuse conduction system involvement

A case of co-existing tachycardia and bradycardia dependent incomplete and complete right bundle branch block (BBB) is reported. The degree of BBB was related to the duration of the preceding cycle length. In addition, more diffuse conduction system disease was suggested by evidence of sino-atrial and His-Purkinje conduction abnormalities.

Transient bifascicular block during Prinzmetal's variant angina

A 49-year-old man had bradycardia-hypotension syndrome and transient right bundle branch block with left anterior fascicular block during an attack of Prinzmetal's angina. Coronary arteriography showed 50 percent obstruction of the proximal left anterior descending artery; subsequently, he had subtotal occlusion at the stenotic portion with ergonovine administration. The occurrence of this conduction abnormality with Prinz metal's angina suggests that diminished blood supply of the proximal His-Purkinje system is the probable mechanism.

Tachycardia-dependent left posterior hemiblock

A patient with intermittent tachycardia-dependent left posterior hemiblock is reported. Electrocardiographic patterns of complete and incomplete block were documented. Identification of the electrocardiographic characteristics of intraventricular conduction defects is aided when they are intermittent. The difficulty in diagnosing incomplete left posterior hemiblock, and the possible masking of the signs of previous inferior infarction by left posterior hemiblock are emphasised.