The effects of digoxin on the electrocardiogram after strenuous exercise in normal men

Effects of digoxin on electrocardiogram in patients with acute atrial fibrillation--a randomized, placebo-controlled study. Digitalis in Acute Atrial Fibrillation (DAAF) Trial Group

BACKGROUND

Studies of healthy volunteers or patients in sinus rhythm have indicated that treatment with digoxin produces characteristic changes in the electrocardiogram (ECG). No randomized, placebo-controlled studies are available and no study has investigated the effect on ECG in patients with atrial fibrillation.

HYPOTHESIS

In a substudy to a trial comparing the therapeutic effect of intravenously administered digoxin with placebo in patients with acute atrial fibrillation, we investigated these effects as well as the relation between ECG changes and serum concentration of digoxin.

METHODS

In all, 167 patients were included. Standard ECGs recorded at baseline, and at 2, 6, 12, and 16 h after randomization were digitized, and changes in RR-intervals, QRS width, ST-segment amplitude at 60 ms after the J point, T-wave amplitude, and QTc interval were calculated. Furthermore, the correlation between the serum concentration of digoxin at 16 h after inclusion and changes on the ECG was analyzed.

RESULTS

Compared with placebo, digoxin resulted in an increase in RR-interval (p < 0.0001), a decrease in ST-segment and T-wave amplitude (p = 0.009 and p = 0.002, respectively), and in the QTc interval (p = 0.01). These changes were present 2 h after the first dose, but were more pronounced after 16 h. There was no significant correlation between serum concentration of digoxin and ECG changes at 16 h.

CONCLUSION

Compared with placebo, digoxin produces significant changes on ECG in patients with acute atrial fibrillation. The changes are in accordance with previous findings in individuals in sinus rhythm. There was no correlation between serum concentration of digoxin and ECG changes.

Effect of autonomic blockade on digoxin-induced ECG changes at rest and during exercise in healthy subjects

The effect of pharmacological autonomic blockade on digoxin-induced electrocardiographic changes at rest and during exercise was studied in nine healthy men. The subjects performed bicycle exercise tests on four occasions after: (1) intravenous injection of sodium chloride, (2) intravenous injection of propranolol and atropine, (3) oral ingestion of digoxin 0.5 mg daily for 2 weeks and intravenous injection of sodium chloride, and (4) oral ingestion of digoxin 0.5 mg daily for 2 weeks and intravenous injection of propranolol and atropine. The ST-T segment was significantly depressed after digoxin plus sodium chloride and digoxin plus propranolol and atropine in comparison with sodium chloride only and propranolol and atropine only. The digoxin-induced ST-T changes after sodium chloride and propranolol-atropine injections were not significantly different. Thus, judging from the results of this study, an effect mediated via the autonomic nervous system is an unlikely explanation of digitalis-induced ST-T changes.

Effect of digoxin on the electrocardiogram at rest and during exercise in healthy subjects

The effect of digoxin on the electrocardiogram at rest and during and after exercise was studied in 11 healthy subjects. Exercise was performed on a heart rate-controlled bicycle ergometer with stepwise increased loads up to a heart rate of 170 beats/min. The subjects were studied after peroral intake of digoxin at 2 dose levels and after withdrawal of digoxin. Administration of digoxin induced significant ST-T depression at rest and during exercise even at the small dose (2.4 +/- 0.8 microgram/kg body weight, mean +/- standard deviation). The ST-T changes were numerically small and dose-dependent. The most pronounced ST and T depression occurred at a heart rate of 110 to 130 beats/min. At higher heart rates the ST depression was less pronounced but still statistically significant. During the first minutes after exercise no significant digitalis-induced ST-T depression was seen. This reaction is not of the type usually seen in myocardial ischemia. Fourteen days after withdrawal of the drug there were no significant digitalis-induced ST-T changes at rest or during or after exercise.

The influence of early repolarization variant on the exercise electrocardiogram: a correlation with coronary arteriograms

Sixteen adult patients with S-T segment elevation in their resting electrocardiograms characteristic of early repolarization variant (ERV) and chest pain syndromes of possible myocardial ischemia were evaluated with both treadmill exercise electrocardiography and coronary arteriography. Of 14 patients with normal coronary arteriograms, 13 had their resting S-T elevation return ("normalize") to the isoelectric baseline with physical exercise, while one patient with normal arteriograms and normal left ventricular contractility but moderately elevated left ventricular end-diastolic pressure of unknown etiology developed significant S-T depression with exercise. Two patients with significant coronary atherosclerotic occlusive lesions developed "ischemic" S-T depression during treadmill testing. Symptoms developed during treadmill exercise did not distinguish patients with coronary artery disease from those without. Thus, while ERV at rest may be "normalized" by graded physical exercise in the absence of significant coronary atherosclerosis, the presence of ERV does not prevent the usual electrocardiographic manifestations of exercise-induced myocardial ischemia.

Exercise testing for detection of myocardial ischemia in patients with abnormal electrocardiograms at rest

This review consists of two parts: (1) discussion of the electrophysiologic mechanisms that are believed to produce ventricular repolarization changes during the electrocardiographic stress test, and (2) clinical assessment of the electrocardiographic changes with stress in patients with an abnormal electrocardiogram at rest. In the first part, the mechanisms of S-T segment elevation, S-T segment depression, T wave changes and linked S-T and T wave changes are reviewed. In the second part, all electrocardiographic abnormalities at rest are grouped into four categories: (1) changes that mask the manifestations of ischemia, (2) changes that stimulate or exaggerate the manifestations of ischemia, (3) changes that have no important effect on the manifestations of ischemia, and (4) changes that reproduce the patterns of acute myocardial infarction after an apparent healing. The reported studies of electrocardiographic stress testing in patients who have abnormal electrocardiogram at rest are summarized.

Effects of digitalis on the exercise electrocardiogram in normal adult subjects

Controversy continues regarding the effects of administration of digitalis upon the exercise electrocardiogram. Thus, maximal treadmill exercise tests were performed before and two weeks after administration of 0.25 mg of digoxin daily in 15 normal subjects (documented by cardiac catheterization and coronary arteriographic studies). Administration of digitalis induced abnormal findings on exercise tests in all 14 subjects with serum levels of digoxin greater than or equal to 0.5 ng/ml; however, at workloads greater than 75 to 90 percent of maximal predicted heart rate, the changes in the ST segment reverted to a normal configuration in all subjects, thereby providing differentiation of digitalis-induced ST-segment alterations from those due to myocardial ischemia at maximal treadmill stress.

TQ-ST segment mapping: critical review and analysis of current concepts

Controversy and confusion surround many aspects of TQ-ST segment mapping today. Technical standards pertaining to the recording and measurement of the TQ-ST deflection have not been uniformly established nor has the correlative value of the deflection as an indicator of myocardial injury been clearly ascertained. The TQ-ST deflection is believed to originate primarily although not exclusively as a result of extracellular potassium accumulation in the ischemic region and subsequent establishment of a transmembrane potential gradient during diastole and systole at the ischemic boundary. Nonspatial factors (including electrolytes, antiarrhythmic agents, heart rate) influence the TQ-ST deflection by altering this gradient. Spatial factors (including ischemic area and shape, electrode location) alter the relative position of the ischemic boundary to the electrode site and as such can be analyzed with the solid angle theorem. Further study of the complex behavior of the TQ-ST segment deflection, particularly in the presence of pharmacologic intervention, is necessary before mapping techniques can be used reliably in clinical studies designed to quantitate and modify ischemic damage.

Effect of lithium on cardiovascular performance: report on extended ambulatory monitoring and exercise testing before and during lithium therapy

To assess the effect of long-term lithium therapy on cardiac arrhythmias and cardiovascular performance, extended ambulatory electrocardiographic monitoring was performed in 12 patients, and rest and exercise electrocardiograms in 10 of 12, before and during lithium therapy. Lithium increased the frequency of premature ventricular contractions in three patients, decreased it in one, and produced no change in eight. Three of four patients with atrial arrhythmias showed improvement during lithium therapy. Exercise performance was unchanged. Although 7 of the 12 patients manifested T wave flattening in the resting electrocardiogram, none had S-T segment displacement at rest or on treadmill exercise. Before lithium therapy, arrhythmias on exercise included premature atrial contractions in four patients, ventricular arrhythmias in four (premature ventricular contractions in four, with couplets in two and with ventricular tachycardia in one). During lithium therapy, exercise did not provoke premature atrial contractions or ventricular tachycardia in any of the patients, but three patients had premature ventricular contractions (with couplets in one case). We conclude that lithium at therapeutic levels may precipitate or aggravate ventricular arrhythmias. When administered to patients with heart disease, factors that interfere with renal clearance of lithium (heart failure, salt restriction, long-term diuretic therapy) must be recognized and doses must be adjusted accordingly. Careful follow-up and electrocardiographic monitoring are advisable if lithium is to be used in the presence of ventricular arrhythmias. Cardiovascular performance as assessed by treadmill exercise testing was not affected by long-term lithium therapy.

Treadmill exercise testing in the presence of digitals therapy or nonspecific ST-T changes: correlation with coronary angiography

Treadmill exercise test results were studied in 93 patients with chest pain who had received digitalis therapy or had nonspecific ST-T changes in the resting electrocardiogram. Results of the treadmill test were correlated with the findings of coronary angiography. A positive treadmill result was defined as horizontal or down-sloping ST segment depression greater than or equal to 1.0 mm. Of the 40 patients with no or insignificant coronary artery disease, 15 had taken digitalis; 4 of the 15 demonstrated a positive response on the treadmill test. Of the 53 patients with coronary artery disease, 21 had taken digitalis; 15 of the 21 displayed a positive response. Among the remaining 32 not on digitalis, 20 had a positive response. The specificity of the treadmill exercise test was 96% in patients with coronary artery disease not on digitalis and whose resting electrocardiogram showed nonspecific ST changes. The specificity of the treadmill test in patients who had received digitalis was 73%. Sensitivity was 63% and 71%, respectively. By utilizing more stringent criteria in the interpretation of the treadmill exercise test (greater than or equal to 1.5 mm ST depression), among the patients on digitalis only 6.7% (1/15) with normal coronary arteries and 48% (10/21) with coronary artery disease had a positive response. With the use of the latter criterion the test was specific in 93% (14/15) of the patients and is usually indicative of coronary artery disease.

Clinical diagnosis

In the majority of instances, the clinical diagnosis of angina pectoris can be made from the history alone. The chest discomfort is characteristically a sensation of deep pressure, is occasionally of burning quality, is found near the sternum, not sharply localized, and has a gradual buildup. Its duration is most often 2-10 min, but may be 30 sec to 30 min or more. Physical effort, emotional strain, large meals, nightmares, or sexual intercourse are common precipitating factors. Nitroglycerin tends to relieve the distress within 1-2 min, but the response is often difficult to evaluate, especially with angina of brief duration or with acute unstable rest angina. Physical examination of the anginal patient is often negative between attacks. During an attack of rest angina, the physical examination usually reveals increased systolic blood pressure and tachycardia. A fourth heart sound and a delayed apical systolic murmur may be found. Premature ventricular beats may develop.

The resting electrocardiogram is normal in the majority of patients with angina pectoris. During the anginal attack, the electrocardiogram usually reveals an increase of the heart rate and ischemic flat or downsloping S-T-segment depressions of 0.08-sec duration or more. The exercise electrocardiogram is most useful when the stress is sufficient to increase the heart rate to 85 or 90% of the predicted maximum for the age of the patient. An abnormal exercise electrocardiogram is found in 80-90% of patients with angina when they are tested by the graded treadmill exercise test of Sheffield and Reeves, but in only 50-60% of those tested by the Master's exercise test.

Varieties of angina pectoris which may differ from the foregoing include: Prinzmetal's variant angina, unstable angina (acute coronary insufficiency, crescendo angina), atypical angina, and angina with syncope.

Angina pectoris must be distinguished from the discomfort of anxiety neurosis, hiatal hernia, cervical spine disease, gallbladder disease, Tietze's syndrome, and post-herpetic neuralgia.