| Patients with permanent pacemakers and sick sinus syndrome (SSS) are considered to have normal cardiac function, but the cardiovascular response to exercise and orthostatism is unknown. Therefore, we studied eight sick sinus syndrome patients (mean 49.8 years), with cardiac pacemakers for $ge$1 year, paced 50% to 100% of the time, and compared them to seven normal subjects (mean 42.6 years) during head upright tilt (40$spcirc$ and 70$spcirc$) and isometric handgrip (30% maximum voluntary contraction). Patients with SSS had a lower resting heart rate, which increased to a lesser extent, than normals, during these stresses, suggesting the presence of chronotropic incompetence.;Moreover, while normals showed the expected rise in systolic and diastolic blood pressure, during isometric exercise, the patients groups showed a plateau in both parameters during the third minute of exercise. Both groups had no significant blood pressure changes during orthostatic challenge.;Echographic parameters of cardiac function, in SSS patients, showed a progressive increase in left ventricular end systolic dimension, with maintained left ventricular end diastolic dimension during isometric exercise suggesting impaired left ventricular contractility. Both parameters were stable in normals.;Peak E (early diastolic flow) decreased in both groups, although the degree of change was larger in SSS patients, suggesting abnormal relaxation of the left ventricle in the SSS group. Peak A (late diastolic flow) significantly increased in both groups, both during tilt and isometric exercise, as a consequence of increased heart rate.;Two parameters of diastolic function, isovolumic relaxation time and deceleration time, were unchanged in both groups during orthostatic and exercise challenge.;In conclusion, the cardiovascular system, in sick sinus syndrome patients, during brief orthostatic challenge, react similarly to normals, but with less magnitude. However, SSS patient's response to isometric exercise was abnormal, with evidence of systolic and diastolic dysfunction. |
