Paradoxical hemodynamic responses to orthostasis in patients with dual chamber pacemakers

he effect of upright posture on hemodynamics of patients with dual chamber (DDD) pacemakers has been largely unexplored. The postural hemodynamic responses in 27 patients with DDD pacemakers were assessed by impedance cardiography calculations of stroke volume and sphygmomanometer measurements of blood pressure. Twenty patients with complete heart block (5 with heart failure) were studied in the VDD mode and 7 patients with sick sinus syndrome and severe chronotropic incompetence (fixed heart rate) were assessed in DVI (4) or VDD (3) modes. In contrast to the responses observed in normals, pacemaker patients' orthostatic responses included: (1) a reduction in systolic, diastolic and mean blood pressures; (2) fixed stroke volume in sick sinus syndrome or heart failure patients, and only modest stroke volume reductions in the remaining patients, and (3) a reduction in systemic vascular resistance. Thus, when assuming the upright position, DDD patients develop a hypotensive response with paradoxical maintenance of stroke volume. Even when AV synchrony is preserved, orthostatic hemodynamic abnormalities are detectable independently of the underlying heart disease. We assume that these abnormalities occur because of the altered autonomic state (autonomic dysfunction) induced by the abnormally depolarized ventricles.