Profound "pacemaker syndrome" in hypertrophic cardiomyopathy

Hypertrophic cardiomyopathy (HC) results in depressed cardiac output and pulmonary congestion from decreased left ventricular diastolic compliance, and in a large subset of patients is further complicated by dynamic left ventricular outflow tract obstruction. Complete atrioventricular (AV) block can induce severe hemodynamic compromise and is particularly dangerous in patients with structural heart disease. The incidence of spontaneous AV block in patients with HC is unknown but is the subject of numerous clinical and electrophysiologic reports.^1-11 The use of β blockers and calcium channel antagonists in patients with HC may independently induce rhythms that compromise normal AV synchrony. "Pacemaker syndrome" refers to the occurrence of symptoms in patients managed with single-rate ventricular pacing who develop the adverse electrophysiologic and hemodynamic consequences of the loss of AV synchrony.¹² Rarely has serious hemodynamic compromise been noted. This syndrome is similar to the hemodynamic events described in 3 patients with HC and profound hemodynamic impairment due to the loss of AV synchrony.