Causal relation between the pressure gradient and left ventricular ejection time in hypertrophic cardiomyopathy

Division of Cardiology, Toronto General Hospital, University of Toronto, Ontario, Canada.

This study was designed to evaluate the relation between severity of obstruction to left ventricular outflow and left ventricular ejection time in hypertrophic obstructive cardiomyopathy. With dual catheters across the left ventricular outflow tract, the pressure gradient and corresponding left ventricular ejection time were measured in 10 patients as the pressure gradient was pharmacologically provoked or abolished, or both. The patients were studied during constant atrial pacing to avoid the potential errors introduced with heart rate correction equations. The pressure gradient was pharmacologically provoked or reduced over a range of greater than or equal to 62 mm Hg per patient. In each patient the left ventricular ejection time varied directly with the pressure gradient (mean r = 0.97, range 0.92 to 1.00). The change in magnitude of the pressure gradient varied directly with the corresponding change in the measured ejection time (mean r = 0.98, range 0.97 to 1.00). When the data from all 10 patients were pooled with use of Weissler's heart rate correction equation, the relation between the corrected left ventricular ejection time and the pressure gradient was still significant and linear (r = 0.86), but less so than in individual patients. This difference was the result of marked interpatient variability in the slope of this linear relation reflecting interpatient differences in other important factors, such as underlying myocardial contractility and stroke volume, that influence left ventricular ejection time. This study demonstrates a clear, direct and highly significant relation between the magnitude of the pressure gradient and the left ventricular ejection time in hypertrophic obstructive cardiomyopathy.(ABSTRACT TRUNCATED AT 250 WORDS)

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