Blood pressure response to transition from supine to standing posture using an orthostatic response algorithm.

Upon standing from a supine position, the normal response is an increase in heart rate to maintain blood pressure (BP). In patients with chronotropic incompetence, heart rate may not increase upon standing, and they may experience orthostatic hypotension (OH). We evaluated a new orthostatic response (OSR) pacing algorithm that uses an accelerometer signal to detect sudden activity following prolonged rest to trigger a 2 minutes increase in pacing rate to 94 bpm. Ten recipients of DDDR pacemakers which contain the OSR compensation algorithm (mean age = 77 +/- 9 years, 8 women) with sick sinus syndrome (n = 6) or atrioventricular block (n = 4) were studied. In all patients BP was measured before and 0.5, 1, 1.5, 2, and 3 minutes after standing at their programmed base rate. A 20 mmHg fall in systolic BP upon standing was observed in five patients (OH patients), while the other five were considered non-OH patients. The measurements were repeated with the OSR algorithm turned on. Mean BP was defined as 1/3 systolic BP + 2/3 diastolic BP. Baseline heart rate was significantly slower in OH patients (62 +/- 2 bpm) than non-OH patients (71 +/- 7 bpm, P < 0.05). In OH patients mean BP increased significantly upon standing (P < 0.05 for all comparisons) with the algorithm ON instead of decreasing with the algorithm OFF, at 1 minute (+3.4 vs -10.3 mmHg), 1.5 minutes (+7.0 vs -4.9 mmHg), 2 minutes (+1.6 vs -6.7 mmHg), and 3 minutes (+2.5 vs -8.5 mmHg). These preliminary results suggest that the OSR algorithm maintains BP upon standing in patients with OH.