Effect of digoxin on the heart in normal subjects: influence of isometric exercise and autonomic blockade: a noninvasive study.

Abstract

1 Eight healthy subjects were studied before digoxin and after successive therapy periods of 1 week 0.125, 0.25 and 0.50 mg of digoxin. The mean serum concentrations (± s. d.) were 0.4 ± 0.2, 0.6 ± 0.3 and 1.4 ± 0.5 nmol I-1, respectively. The effects of digitalis were studied by echocardiography and systolic time intervals at rest and after 3 min handgrip exercise. Effects of simultaneous autonomic blockade induced by atropine and propranolol were also examined. 2 Digoxin in increasing doses slowed the heart rate at rest; with the daily dose of 0.50 mg from 63 ± 10 to 53 ± 6 beats min-', and fractional shortening rose from 28 ± 6 to 33 ± 3% (P < 0.05 for both). Preload, afterload and cardiac output did not change. The electromechanic systolic time index (QS2I) decreased (P < 0.001) and the observed alteration of QS2I was dose-related.3 The influence of digoxin was similar during isometric exercise, except for unchanged fractional shortening. 4 During autonomic blockade digoxin slowed the intrinsic heart rate from 93 ± 6 to 86 ± 6 beats min-' (0.25 mg) and to 83 ± 6 beats min-' (0.50 mg) (P < 0.01 for both). QS2I was shortened (P < 0.01). Echocardiographically determined ejection phase indices remained unchanged. 5 When handgrip stress was induced during autonomic blockade, digoxin evoked a clearcut increase in contractile function, resembling the effects of digoxin alone at rest. Thus, fractional shortening increased by 14% and QS21 decreased by 16 ms (P < 0.01 for both). 6 We conclude that digoxin increases the contractility in normal heart without changes in loading conditions. The rise in inotropy at rest is obvious from both fractional shortening by echo and systolic time intervals. The same takes place during handgrip with autonomic blockade, when the heart lacks sympathetic support. The influence of long-term digoxin on heart rate is partly direct without autonomic mediation. The effect of digoxin is dosedependent.Keywords digoxin isometric exercise autonomic blockade left ventricular contractility echocardiography systolic time intervals

Effects of digoxin and digitoxin on circadian blood pressure profile in healthy volunteers

“…Nocturnal blood pressure changes are generally clinically occult. Decrease in heart rate by digoxin was also more readily noticed at rest than during isometric exercise [7]. This gives clinically relevant information and avoids drawing false conclusions from blood pressure readings under controlled laboratory conditions.…”

“…Blood pressure or heart rate reduction caused by cardiac glycosides in normal subjects described previously had most often occurred when the subjects underwent non-invasive cardiovascular procedures in supine resting conditions [5,6], similar to the night-time sleeping phase of our study rather than daytime activities. Decrease in heart rate by digoxin was also more readily noticed at rest than during isometric exercise [7].…”

Pressor and vascular effects of cardiac glycosides

“…In contrast to these results, Partanen et al found that 1-week oral treatment with increasing doses of digoxin (0·125, 0·25 and 0·5 mg daily) failed to alter significantly SBP values at rest during autonomic blockade and isometric exercise at any of the doses used, but significantly lowered DBP values [5]. This marked fall in DBP was not directly pointed out in the results or even discussed.…”

Pressor and vascular effects of cardiac glycosides

“…In contrast to these results, Partanen et al . found that 1‐week oral treatment with increasing doses of digoxin (0á125, 0á25 and 0á5 mg daily) failed to alter significantly SBP values at rest during autonomic blockade and isometric exercise at any of the doses used, but significantly lowered DBP values [5]. This marked fall in DBP was not directly pointed out in the results or even discussed.…”

“…They have been grouped into the influence of cardiac glycosides on blood‐pressure values and on vascular effects respectively. In some of the studies cited [5], the relationship between cardiac glycosides and blood pressure was not the main thrust of the study, so that even significant changes in blood‐pressure values were not necessarily discussed by the authors.…”