This case demonstrates that pseudo-type II second-degree AV block from a left bundle branch parasystolic focus can be paradoxically worsened by propranolol and successfully treated with isoproterenol or quinidine.
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May warrant avoiding propranolol in suspected fascicular parasystole; leaves open validation of isoproterenol or quinidine in larger cohorts.
This report describes a patient with pseudo-type II second-degree AV block due to an intermittent parasystolic focus located in the left bundle branch. A paradoxical increase in the fascicular rate was seen following intravenous propranolol, and fascicular extrasystoles were suppressed after intravenous isoproterenol treatment. All propagated fascicular extrasystoles were conducted to the ventricle with incomplete or complete right bundle branch block and a decrease in the H'-V interval compared to the H-V interval during sinus rhythm. Treatment with oral quinidine abolished fascicular extrasystoles without worsening of AV conduction.
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Nalos et al. (1987) studied this question.
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