We appreciate the interest of Prof. Cotrim in our recent report showing that earlier onset of left ventricular outflow tract gradients during physiologic exercise is associated with impaired exercise performance in patients with hypertrophic cardiomyopathy (HC). In our study, gradients measured upright during exercise or supine immediately after exercise were similar. Therefore, we concluded that the 2 approaches may be considered equivalent for clinical purposes. However, Prof. Cotrim questions this view, arguing that gradients assessed after exercise in the upright position may be greater than those measured supine and therefore more accurately reflect the magnitude of obstruction occurring during physiologic exercise provocation. This observation, however, is based on patients with HC actively treated with β blockers, verapamil, or both, agents that may act as potential modifiers of gradients in response to postural changes. In this respect, our study differs from those previous studies, in that each of our 74 patients were assessed in the absence of pharmacologic treatment and therefore under conditions more closely reflecting purely physiologic modifications of subaortic gradients with physical activity. This crucial difference in the enrollment criteria may well explain the discrepancy between our data and those in previous studies.

It is common practice at many centers in Europe and the United States to measure postexercise gradients in the supine position, a practice that is also in accordance with current international guidelines regarding treadmill protocol. Therefore, it is of relevance to have shown that upright and supine assessment of outflow gradients are equally acceptable for clinical decision making. Specifically, despite subtle individual differences between gradients measured by the 2 approaches, each of our 22 patients who achieved marked gradients (i.e., ≥50 mm Hg) in the supine position after exercise exceeded the same threshold while upright during exercise.

Ultimately, all the available data underscore the dynamic nature of left ventricular outflow obstruction in HC and emphasize that exercise echocardiography is an important adjunct to the clinical evaluation of such patients when outflow obstruction is absent at rest (particularly in the presence of heart failure symptoms). When feasible, evaluation of provokable obstruction should include all stages of exercise and recovery, upright and supine, to provide the most precise assessment of the timing, as well as the magnitude, of dynamic left ventricular outflow gradients in HC.