Physiologic Benefits of Rate Responsiveness

Abstract

Increases in metabolic demand in response to routine activities and exercise are met through greater cardiac output and oxygen delivery. Patients with fixed-rate pacemakers cannot increase heart rate and must rely solely on increases in stroke volume to provide the necessary adjustments in cardiac output. These compensatory stroke volume increases limit the fixed-rate pacemaker patient's ability to meet the demand of their daily routine. A physiological, rate responsive pacemaker was studied and it was found to increase maximum exercise tolerance from 4.4 +/- .62 METS paced VVI at 65 ppm to 8.1 +/- .71 METS when the same patients were paced rate responsively at an average rate of 91 +/- 3.8 ppm. Animal studies were used to quantify the limitation in stroke volume reserve. Maximum increases of 55.8 +/- 3.7% over resting values were seen in animals in complete heart block at pacing rates of 100 ppm during strenuous exercise. Higher pacing rates increased cardiac output at the same exercise intensity, from 4.94 +/- .72 lpm at 100 ppm to 7.66 +/- 1.02 lpm at 250 ppm. A pacemaker that increases pacing rate in response to greater metabolic demand will maintain stroke volume and end-diastolic volume at near normal values while providing significant improvement in cardiac output and work capacity.

Indications for permanent pacing in dogs and cats

“…Younger dogs seem to be good candidates for physiologic pacing because they can potentially live longer and may be more active, although older dogs may also benefit because of concurrent structural heart disease [110]. Working, hunting, and agility dogs may benefit from AV synchronous pacing, and a short-term study revealed 44% increase in echocardiographically determined stroke volume and 28% increase cardiac output during VDD pacing compared with fixed-rate VVI pacing [139]. Whether these data are confirmed during exercise is uncertain, although an experimental study suggests a limitation in stroke volume reserve during fixed-rate VVI pacing [140].…”

“…In veterinary medicine, one retrospective study analyzed the perceived symptomatic improvement in quality of life or exercise tolerance by asking owners to complete a quality of life questionnaire, but no statistically significant differences were identified between the two pacing modalities. Whether there are no quality of life benefits, the benefits are too subtle to be detected by the owners in otherwise sedentary dogs, or the quality of life questionnaire was inappropriately designed to document clinical benefits is difficult to determine [139].…”

Should physicians instead of industry representatives be the main actor of cardiac implantable electronic device follow-up? (Super Follow-up)

“…The necessity of a rate-adaptive mode or hysteresis was evaluated, and the presence or absence of over- or undersensing, cross-talk, or far-field sensing was recorded during each follow-up. The rate-adaptive mode was supposed to be “on” in patients with SSS and atrial fibrillation (AF) with slow ventricular response, whereas it was supposed to be “off” in patients with only AV block (5). …”

VDD pacing in dogs: When, why and how to perform single-lead atrial synchronous, ventricular inhibited (VDD) pacing

“…8 Whether these results are similar during exercise is uncertain but an experimental study of complete heart block in dogs suggests there is a limitation in stroke volume reserve during fixed rate pacing. 14 Shapland et al identified the maximum increase in stroke volume during strenuous exercise was 55.8% over resting values at a pacing rate of 100 bpm and cardiac output increased from 4.94 L/min at 100 bpm to 7.66 L/min at 250 bpm at the same exercise intensity. 14 It is therefore hypothesized that the hemodynamic benefit identified during physiologic pacing at rest may translate into maintenance of stroke volume and end-diastolic volume near normal values, while simultaneously augmenting cardiac output and exercise capacity, in dogs with naturally acquired 3rd degree AV block.…”