Left Ventricular Outflow Tract Gradient Variability in Hypertrophic Cardiomyopathy

Background: The presence and magnitude of left ventricular outflow tract (LVOT) obstruction directs the management algorithm in symptomatic patients with hypertrophic cardiomyopathy (HCM). Although it is well known that the degree of LVOT obstruction is dynamic and dependent upon ventricular load and contractility, the magnitude and potential impact of the day-to-day variability seen in practice has not been well appreciated. Hypotheses: We hypothesized that LVOT gradient variability in HCM has an impact on clinical decision-making. Methods: A total of loo HCM patients (mean age, 58 +/- 13 years; 47% male) underwent comprehensive 2-dimensional Doppler transthoracic echocardiography and cardiac catheterization with transseptal measurement of left-sided pressures. All studies were performed within 48 hours of one another. Results: The correlation of LVOT gradients from both methods performed at different times had a wide scatter with the 95% confidence limits of agreement being +/-84 mm Hg. For classifying patients as having severe LVOT obstruction on the basis of either method (<30 vs >= 30 mm Hg), discrepant results occurred in 21% Of patients. To confirm the accuracy of Doppler measurements, 15 studies were performed with simultaneous measurement of LVOT gradient, which revealed a very strong correlation (r = 0.98,p < 0.0001) with 95% confidence limits of agreement +/-12 mm Hg. Conclusions: in patients with HCM, LVOT gradient measurements are routinely obtained to characterize the severity of obstruction. However, these data demonstrate the, marked variability of the LVOT obstruction, which must be considered when determining appropriate therapy in symptomatic patients.