Physiologic Benefits of Rate Responsiveness

Ľaugmenfation du besoin métabolique ou cours de ľexercice est fournie par une hausse du débit cardiaque et de ľapport ?oxygène. Les malades porleurs ?un stimuluteur à fréquence fixe ne peuvent pas augmenter la fréquence cardiaque dont dépend ľaugmentation du débil systolique. Nous décrivons un stimulateur capable ?augmenter sa fréquence suivant ľuctivité auriculaire. Par cette méthode nous avons observé un meilleur débit cardiaque, de ľordre de 55 ± 3.7%. Ce stimulafeur améliore donc la performance cardiaque pendant ľexercice. Increases in metabolic demand in response lo routine activities and exercise are met througb grealer cardiac output ond oxygen delivery. Putienls with fixedrate pacemakers cannot increase heart rate and must rely solely on increases in stroke volume to provide the necessary adjustments in cardiac output. These compensatory strofte volume increases limit the fixedrate 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 lo quantify the limitation in stroke volume reserve. Maximum increases of 55.8 ± 3.7% over resting vulues 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 Ipm at 100 ppm lo 7.66 ± 1.02 Ipm at 250 ppm. A pacemaker that increases pacing rate in response to grealer metabolic demand will maintain stroke volume and enddiastolic volume at near normal voiues while providing significant improvement in cardiac output and work capacity.