I would like to congratulate Wittlieb-Weber et al . on their publication highlighting the variability of left ventricular outflow (LVOT) velocities during exercise in apparently healthy children. Their study also demonstrated that exercise in the upright position generates higher LVOT velocities than exercise in the supine position.

Recently it has been documented that patients with symptomatic “nonobstructed” hypertrophic cardiomyopathy can generate gradients if they are postprandial and undergo upright exercise echocardiography. It appears that when the heart is vigorously contracting in the setting of low preload and/or low afterload, higher LVOT velocities are to be expected. Environmental influences such as room temperature, eating and or drinking before exercise, and the specific fluid consumed may have an impact on hemodynamics.

The challenge is to assess intracardiac anatomy and measures of systolic and diastolic function in the context of these environmental variables. In addition, there should be a detailed assessment of specific cardiac anatomy before exercise to help predict whether a patient has an anatomic predisposition to develop pathologic obstruction with exercise. Cognizance of the presence of an abnormally long anterior mitral valve leaflet and abnormal chordal attachments, along with increased number, size, and position of papillary muscles, would increase one’s ability to predict the presence of obstruction that is disease related. In addition to these left ventricular findings, the presence of abnormal RV function and wall thickness can give additional support for diagnosing a myopathic heart.

Invasive hemodynamic monitoring in patients with nonobstructed hypertrophic cardiomyopathy has documented abnormal right ventricular diastolic function along with increased right ventricular volume and higher filling pressures compared with normal controls. These hemodynamic findings are in direct contrast to what one would expect in a healthy heart that has inadequate preload in the face of low afterload. Ultimately, one needs to have better measures of preload and afterload during stress to help differentiate a physiologic response from a pathologic response. Clearly, increasing left-sided obstruction with elevated right-sided pressure results in lower coronary perfusion pressure that is more consistent with disease and may be more predictive of a higher risk patient.

Finally, if a child has an abnormal increase in LVOT velocity in response to exercise, a comprehensive evaluation should be pursued to identify and treat the common conditions that would result in increased LVOT velocity (dehydration, orthostatic hypotension, postural orthostatic tachycardia syndrome, and autonomic instability). The interpretation of stress test results must be patient specific and take into account the physiologic state of a patient at the time of exercise testing.