Exercise-induced impairment of diastolic time in patients with X syndrome

Since an abnormal shortening of diastolic duration during exercise in the patients with coronary artery disease was demonstrated, time course of diastolic period (cardiac cycle minus electromechanical systole) calculated from polycardiographic recording has been assessed in patients with X syndrome and in normal age-matched subjects during supine ergometer exercise. All patients with X syndrome had positive exercise stress response (more than 0.1 mV of ST segment depression). Duration of diastole expressed as percent of cardiac cycle was significantly shorter at the intermediate steps and at the peak of exercise in patients with X syndrome compared with normal subjects (p less than 0.05). When the relationship between heart rate and diastolic time was examined, an inverse nonlinear regression was found both in normal subjects and in patients with X syndrome. The exercise values of diastolic time observed in patients with X syndrome were significantly shorter than those predicted as normal diastolic time heart rate relation. Thus the patients with X syndrome demonstrated abnormalities in the decrement of diastolic time with exercise. We hypothesized that this disproportionate shortening, by reducing subendocardial blood flow, might induce a worsening of ischemic response to exercise.