Electrophysiological studies in patients with prolonged HV intervals should include procedures to expose bradycardia-dependent AV block, which can be triggered by premature beats.
May warrant testing for bradycardia-dependent AV block in EP studies of prolonged HV; single case leaves open broader adoption.
Symptomatic bradycardia-independent atrioventricular block occurred in a patient with right bundle-branch block, left anterior hemiblock, and prolonged HV interval. The arrhythmia, triggered by a spontaneous or induced premature beats, appeared when the post-extrasystolic PP and HH intervals increased to a critical value. Reinitiation of atrioventricular conduction required the presence of ventricular escapes. Bradycardia-dependent atrioventricular block was related to either an enhanced or slightly rising slope of diastolic depolarization, or to a decrease in membrane responsiveness. The patient also, most probably, had tachycardia-dependent atrioventricular block. Both types of conduction disturbance occurred in the same part of the intraventricular conducting system, either in the low His bundle or left bundle-branch or its posteroinferior division. It is suggested that the electrophysiological study of cases with prolonged HV intervals should include procedures which can expose bradycardia-dependent atrioventricular block.
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Castellanos et al. (1975) studied this question.
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