Effects of digitalis on normal and abnormal left ventricular segmental dynamics

The effect of chronic digitalization on pump function in systolic heart failure

BACKGROUND

Short- and intermediate-term use of cardiac glycosides promotes inotropy and improves the ejection fraction in systolic heart failure.

AIM

To determine whether chronic digitalization alters left ventricular function and performance.

METHODS

Eighty patients with mild-to-moderate systolic heart failure (baseline ejection fraction < or =45%) participated from our institution in a multi-center, chronic, randomized, double-blind study of digitalis vs. placebo. Of the 40 survivors, 38 (20 allocated to the digitalis arm and 18 to the placebo arm) were evaluated at the end of follow-up (mean, 48.4 months). Left ventricular systolic function was assessed by both nuclear ventriculography and echocardiography. The ejection fraction was measured scintigraphically, while the ventricular volumes were computed echocardiographically.

RESULTS

The groups did not differ, at baseline or end-of-study, with respect to the ejection fraction and the loading conditions (arterial pressure, ventricular volumes and heart rate) by either intention-to-treat or actual-treatment-received analysis. Over the course of the trial, the digitalis arm exhibited no significant increase in the use of diuretics (18%, P=0.33), in distinction from the placebo group (78%, P=0.004), and a longer stay on study drug among those patients who withdrew from double-blind treatment (28.6 vs. 11.4 months, P=0.01).

CONCLUSION

Following chronic use of digitalis for mild-to-moderate heart failure, cross-sectional comparison with a control group from the same inception cohort showed no appreciable difference in systolic function or performance. Thus, the suggested clinical benefit cannot be explained by an inotropic effect.

Heart failure in patients with preserved left ventricular systolic function: do digitalis glycosides have a role?

It is being increasingly appreciated that a substantial number of patients with congestive heart failure (CHF) have relatively preserved systolic function. Although these individuals appear to have a somewhat better prognosis than those with low ejection fractions, they experience significant symptoms and frequently require hospitalization. In these patients, CHF is often attributed to left ventricular diastolic dysfunction, but this represents a potentially misleading over-simplification. In contrast to CHF associated with left ventricular systolic dysfunction, little is known about how to treat patients with preserved systolic function. Perhaps the major point of consensus has been that the use of digitalis glycosides is inappropriate in this group. Unexpectedly, however, in the recently completed Digitalis Investigators Group trial, a subgroup of nearly 1,000 patients with radionuclide ejection fractions > or = 45% experienced a similar reduction in heart failure endpoints with digoxin therapy as patients with 25% to 44% ejection fractions. The purpose of this article is to review the diverse causes of CHF with preserved systolic function and to examine the potential mechanisms by which digoxin may be producing beneficial effect in this setting.

Acute hemodynamic effects of digoxin alone or in combination with other vasoactive agents in patients with congestive heart failure

Although digitalis preparations have been in use for greater than 200 years, it is only within the last 2 decades that the central hemodynamic and neurohumoral effects occurring over several hours following intravenous administration of digoxin have been investigated in patients with congestive heart failure (CHF). Although digoxin has been shown to stimulate myocardial contractility in tissue preparations, its positive inotropic activity does not consistently translate into improvements in hemodynamic measurements in humans. Digoxin given intravenously results in increased cardiac index and decreased heart rate, left ventricular filling pressure, and right atrial pressure, as well as in acute attenuation of neurohumoral abnormalities, in patients with chronic CHF who have abnormal baseline hemodynamic measurements. Unlike other drugs with positive inotropic activity, however, digoxin does not influence hemodynamics in normal volunteers or in CHF patients in whom hemodynamics have been normalized with other therapies. These differing effects may be related to the drug's diverse peripheral vascular effects in CHF patients in whom vasodilation may occur in comparison with those that occur in normal subjects in whom the peripheral vasoconstrictor effects may prevent the inotropic effects of the drug from being translated into an increase in cardiac output. The hemodynamic effects of digoxin in patients with chronic CHF due primarily to diastolic dysfunction have not been fully investigated. Intravenous digoxin produces hemodynamic effects in patients with CHF associated with acute myocardial infarction, but these changes are small compared with those resulting from the administration of dobutamine. Digoxin does not appear to influence hemodynamic measurements in patients with right ventricular dysfunction unless concomitant left ventricular failure is present. In patients with chronic left ventricular dysfunction, the hemodynamic effects of intravenous digoxin and vasodilators are enhanced when these agents are given in combination.

Effects of captopril treatment on left ventricular remodeling and function after anterior myocardial infarction: comparison with digitalis

The effects of captopril and digoxin treatment on left ventricular remodeling and function after anterior myocardial infarction were evaluated in a randomized unblinded trial. Fifty-two patients with a first transmural anterior myocardial infarction and a radionuclide left ventricular ejection fraction less than 40% were randomly assigned to treatment with captopril (Group A) or digoxin (Group B). The two groups had similar baseline hemodynamic, coronary angiographic, echocardiographic and radionuclide angiographic variables. Among the 40 patients (20 in each group) who were followed up for 1 year, echocardiographic end-diastolic and end-systolic volumes were unmodified in Group A and global wall motion index was improved (p less than 0.01); in Group B, end-diastolic and end-systolic volumes increased (p less than 0.001 for both) and global wall motion index was unchanged. Rest radionuclide ejection fraction increased significantly in both groups (p less than 0.001, Group A; p less than 0.005, Group B). A comparison of the changes in the considered variables between the two groups after 1 year of treatment showed a difference in end-diastolic (p less than 0.005) end-systolic volumes (p less than 0.001) and global wall motion index (p less than 0.005) without differences in radionuclide ejection fraction, which improved to a similar degree in both groups. The results of this study suggest that captopril therapy, started 7 to 10 days after symptom onset in patients with anterior myocardial infarction and an ejection fraction less than 40%, improves both left ventricular remodeling and function and prevents left ventricular enlargement and in these patients performs better than digitalis.

Combination of positive inotropic and vasodilating substances in congestive heart failure

Therapy combining vasodilators and inotropic agents is considered to be one of the most powerful means of improving cardiac function in patients with congestive heart failure (CHF). The vasodilators enhance the effectiveness of inotropic agents by providing a reduction in preload and/or afterload. Inotropic drugs with different mechanisms of action, such as digitalis glycosides, ephedrine, dopamine, dobutamine, ibopamine, terbutaline, salbutamol, pirbuterol, prenalterol, amrinone, and milrinone, have been tested in combination with vasodilators with a predominant effect on preload (nitrates, molsidomine), with a predominant effect on afterload (hydralazine, nifedipine), or with a balanced action on both arterial and venous beds (nitroprusside, prazosin, captopril), showing positive results. The problem of the combination of digitalis glycosides and vasodilators with different sites of action has been considered by our group. In 42 patients with CHF, digoxin (DIG, 0.01 mg/kg intravenously) was tested in combination with molsidomine (MLS, 4 mg sublingually) (12 patients), a nitrate-like agent with a predominant vasodilating action on the capacitance vessels, nifedipine (NFP, 10 mg sublingually) (22 patients), a Ca2+ antagonist drug with a predominant action on the resistance vessels, and captopril (CPT, 25 mg orally) (8 patients), an ACE inhibitor with a balanced effect on both preload and afterload. The combination DIG plus MLS caused a reduction in left ventricular filling pressure (LVFP) greater than that achieved with either agent alone. The hemodynamic improvement was obtained without side effects, in spite of the striking fall in preload. We stress that this investigation was performed on patients with CHF following acute myocardial infarction.(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of digitalis on the normal and the failing heart

Although it has been known for more than a century that digitalis glycosides exert a powerful beneficial effect on patients with heart failure, atrial fibrillation and a rapid ventricular rate, it was believed for many years that the drug exerts this clinical effect primarily by slowing the heart rate. It was also thought that the extra-cardiac vascular actions of digitalis might be responsible for its therapeutic effect. It has now been established that cardiac glycosides cause arteriolar and venous constriction in a variety of mammalian species including human beings, and that this vasoconstriction involves the coronary vascular bed as well, but it is believed that these actions are not responsible for any beneficial clinical effect. A variety of investigations on cardiac muscle in vitro, anesthetized and conscious dogs and anesthetized and conscious human subjects have shown that cardiac glycosides improve the contractility of failing mammalian myocardium. It has become clear that digitalis also stimulates the contractility of the nonfailing heart. The degree of augmentation of contractility induced by cardiac glycosides is related inversely to the baseline contractile state. Myocardial oxygen consumption, which is increased in the normal heart by the positive inotropic action of glycosides, is actually reduced or remains constant in the failing heart. Cardiac glycosides increase the contractility of the globally ischemic heart, but their actions in chronic ischemic heart disease with regional impairment of function are complex. Deterioration of segmental performance occurs in ischemic and necrotic segments, while improvement of contractility occurs in adjacent normal segments.(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of discontinuing maintenance digoxin therapy in patients with ischemic heart disease and congestive heart failure in sinus rhythm

To evaluate the importance of oral maintenance digoxin therapy in chronic congestive heart failure (CHF), 24 patients in sinus rhythm on maintenance digoxin for documented CHF were studied prospectively on and off the drug. The average duration of therapy was 39 months (range 2 to 180). All 24 patients had documented coronary artery disease (CAD): 22 were in New York Heart Association functional class III and 2 in class II. Twenty-one patients (88%) were receiving diuretic or vasodilator therapy, or both, before digoxin discontinuance. At 1 month off digoxin and with no increase in doses of other medications excepting minor increases in antianginal therapy in 2 patients, no difference was observed in the group as a whole in symptoms, resting heart rate, arterial blood pressure, physical findings, weight, cardiothoracic ratio, radiographic signs of pulmonary congestion, radionuclide left ventricular ejection fraction (LVEF), duration of symptom-limited treadmill exercise (14 patients), or CHF score, compared with evaluation during maintenance digoxin therapy. Similar results were obtained in a subgroup of 9 patients with a resting LVEF less than 0.35 (0.27 +/- 0.02; mean +/- standard error of the mean). Six patients had a decrease and 5 patients an increase in LVEF of greater than or equal to 0.05 units after cessation of digoxin. Off digoxin, the CHF score increased by only 1 point in 2 patients, but also decreased in 2 patients. Thus, in this study population comprised of patients with CAD with documented CHF, most of whom were receiving diuretics or vasodilators, or both, digoxin withdrawal had no adverse clinical or hemodynamic effects.

Effects of digoxin on left ventricular function in coronary artery disease patients

To assess whether digitalis modifies or prevents the deterioration of the left ventricular ejection fraction and wall motion during acute ischemia, we performed gated blood pool radionuclide ventriculograms in 15 patients with angiographically documented coronary artery disease. All patients were studied in the resting state and during maximal supine bicycle exercise, both before and 1 hour after 1 mg intravenous digoxin. There was no significant difference, pre-digoxin vs post-digoxin, in exercise tolerance (415 +/- 84 vs 418 +/- 107 seconds), number of segments with abnormal resting wall motion (12 vs 11) or exercise wall motion (21 vs 19). Ten patients developed angina during the same exercise load, irrespective of digoxin administration. Twelve patients had subnormal left ventricular ejection fraction during exercise pre-digoxin, vs 13 patients post-digoxin (P = ns). In the resting state, the left ventricular ejection fraction was higher after digoxin (53 +/- 14% pre vs 58 +/- 14% post, P less than 0.05). During exercise, however, the left ventricular ejection fraction was not significantly improved after digoxin (50 +/- 16% pre vs 53 +/- 17% post, P = ns). These data indicate that although acute administration of digoxin improves the resting left ventricular function, it does not improve exercise tolerance to angina. Furthermore, intravenous digoxin does not appear to prevent the deterioration of left ventricular wall motion and ejection fraction during exercise induced ischemia.

Hemodynamic pattern following K-strophanthin in normal and coronary artery disease patients

Hemodynamic effects of K-strophanthin (0.005 mg/kg i.v.) were evaluated in 7 normal and in 13 non-failing coronary artery disease patients (CAD). Volumetric parameters were obtained by single plane left ventricular angiography. The indexes of "pump" function, the end-systolic pressure-volume relationship and the ratio of peak pressure to systolic volume were also evaluated. Heart rate was maintained constant by atrial pacing. In normal subjects K-strophanthin exerted small effects without peripheral vasoconstriction. CAD patients showed different response to K-strophanthin in vascular tone: an increase (Group 1) or a decrease (Group 2) in total systemic resistance (TSR). No significant differences were found in basal values between the two CAD groups. In Group 2 the indexes of "pump" function increased after K-strophanthin and the end-systolic pressure-volume points shifted upward and to the left, while in Group 1 no improvement in cardiac function was observed and the end-systolic pressure-volume points shifted upward and to the right. Furthermore, we found a direct significant correlation between the percent changes of TSR and end-systolic volume index, and a negative significant correlation between the percent changes of TSR and stroke volume index. Our results show that K-strophanthin in CAD non-failing patients can have either a positive effect or a lack of improvement in ventricular performance. These effects correlate with changes in total systemic resistance.

Limitations of post-extrasystolic potentiation in assessing regional myocardial viability in man

To investigate the usefulness of regional response to post-extrasystolic potentiation as a predictor of left ventricular viability in patients with coronary artery disease, 46 patients underwent calibrated biplane left ventricular cineangiography during which a single, timed ventricular premature contraction was introduced.

RESULTS

Of 758 normal or hypokinetic segments, 486 (64.1%) showed a positive response to post-extrasystolic potentiation. Of 116 akinetic or dyskinetic segments, only 51 (43.9%) showed a positive response to post-extrasystolic potentiation (P less than 0.001). Because akinetic or dyskinetic areas would not be expected to respond to post-extrasystolic potentiation based on animal laboratory data, alternative explanations were sought to explain such positive response in man. Analysis of percent change in chord length of normal or hypokinetic segments adjacent to akinetic or dyskinetic segments that did or did not respond to post-extrasystolic potentiation revealed (10.2% +/- 1.2%) vs (1.3% +/- 0.7%) improvement, respectively (P less than 0.001) (mean +/- SE).

CONCLUSION

Passive rather than active events may be responsible for "improved" regional wall motion following post-extrasystolic potentiation in akinetic or dyskinetic regions. If unrecognized, these factors may lead to improper interpretation of "intervention ventriculography" utilizing post-extrasystolic potentiation.