[Clinical experiences with 3 different rate-adaptive pacemaker systems]. / Klinische Erfahrung mit drei verschiedenen frequenzadaptiven Schrittmachersystemen.

Physiological stimulation can be achieved by either bifocal or rate responsive pacing. The latter pacemakers adapt the heart rate to physical activity by biological signals. Of many possible approaches only three pacemaker systems for rate responsive pacing are available: the QT pacemaker (Tx or Quintech), the respiratory Biorate pacemaker and the activity detecting Activitrax. First our own experiences (8 QT, 6 Biorate, 8 Activitrax pacemakers) and a survey of 95 QT- and 37 Biorate pacemakers from 11 centers are reported. The Biorate pacemaker functions without any problems, its present disadvantage is limited programmability. With the Tx pacemaker failing frequency adaptation (26%) was found more often in the early series, mostly due to voltage polarisation at the tip of the electrode. The Activitrax pacemaker gives satisfactory frequency adaptation, largely depending on the activity of the muscles of the shoulder and pectoral region.

Role of the renin-angiotensin system in the development of congestive heart failure in the dog as assessed by chronic converting-enzyme blockade.

Hormonal factors may be important in the regulation of peripheral vascular resistance (PVR) in congestive heart failure (CHF). The role of the renin-angiotensin system in the development of CHF was studied in 16 unanesthetized dogs. CHF was induced by rapid right ventricular pacing, with and without chronic converting-enzyme inhibition (CEI) by captopril. The hemodynamic changes and the activity of renin, aldosterone, norepinephrine and vasopressin were studied. The control dogs showed a greater decrease in cardiac output and a greater increase of mean pulmonary artery pressure than the captopril-treated group. In the group with CEI, only a small, transient increase in PVR was observed during the development of CHF; in the control group, there was an increase of 94% of basal values. The control group showed a continual increase of renin, aldosterone and norepinephrine. Four control dogs showed an inappropriately high secretion of arginine vasopressin. The increase of sympathetic nervous activity was only insignificantly attenuated by angiotensin II inhibition and was without a considerable influence on PVR except for an early transient increase in vascular tone. In our animal model, the renin-angiotensin system plays an important role in the regulation of PVR in CHF. In this kind of CHF the sympathetic nervous system appears to be of minor importance for the long-term regulation of PVR. Plasma arginine vasopressin levels were increased in control dogs; this increase may contribute to the increased vascular tone.

Captopril in the long-term treatment of essential hypertension: changes in the renin-angiotensin-aldosterone system.

We investigated changes in the renin-angiotensin-aldosterone system in seven patients with essential hypertension during treatment with captopril (SQ 14225) (300 to 450 mg/day) for 12 months. While blood pressure decreased, the plasma-renin concentration increased to 700 percent of the initial value (6.1 +/- 2.5 ng angiotensin l/ml . h) and angiotensin I increased to about 300 percent of the basal value (179 +/- 32 pg/ml). Converting enzyme inhibition resulted in a 30 percent decrease in plasma angiotension II levels from a basal level of 66 +/- 21 pg/ml. Plasma aldosterone decreased 52 percent from 63 +/- 13 pg/ml initially. These changes in hormone levels were maintained throughout the study. There was no significant change in serum sodium and serum potassium concentration.