Enhanced rate response algorithm for orthostatic compensation pacing

Upon orthostatic stress after a period of rest, the heart rate increases ra pidly to maintain cardiac output and minimize the fall in arterial pressure . Pacemaker patients are often prone to a deficient response to orthostatic stress. This may cause lightheadedness and, in rare patients with autonomi c dysfunction, syncope. To alleviate these undesirable consequences, an enh anced rate response algorithm was developed using an accelerometer. The pac emaker generates two signals from its accelerometer: instantaneous activity level (Act) and long-term change in activity level (ActVar). Low values of both Act and ActVar indicate a resting state. An increase in Act while Act Var remains low indicates the onset of motion after prolonged rest. Upon de tecting this transition, the algorithm increases the pacing rate to a progr ammable orthostatic compensation rate for a programmable duration. A taped- on pacemaker with this algorithm was evaluated in three healthy women and t wo healthy men, 36 +/- 8 years of age. Electrocardiogram and ventricular pa cing pulses were recorded by a 24-hour ambulatory system. Each trigger of t he orthostatic compensation rate wets verified against a >10 beats/min incr ease in heart rate, a response classified as appropriate. The overall speci ficity of the algorithm among the five subjects wets 78%. The nocturnal spe cificity (10 PM to 7 AM) was 98%, considerably higher than during daytime ( 72%). In conclusion, a pacing algorithm to alleviate orthostatic stress was developed, which was highly specific during the night hours.