Digitalis intoxication — management and prevention

Abstract

Although the cardiac glycosides are most useful drugs, morbidity and mortality may result from their presence within the body in excessive amounts; the symptoms and signs of digitalis excess are commonly referred to as digitalis intoxication. Its incidence seems to be increasing due, in part, to the greater awareness of physicians and to the increased longevity of the population in general and, in particular, of those with cardiovascular disease. Adequate data concerning its actual incidence, however, are lacking. The known predilection of older patients probably is due to the fact that heart disease causing congestive failure, for which these drugs are given, occurs primarily in older persons and is not due to any factor of age per se. Nearly all of the unwanted effects of digitalis are due to overdosage, either relative or absolute, and of these effects our major concern is the occurrence of cardiac arrhythmias. Although ST-T and QT interval changes usually appear in the electrocardiogram after digitalis administration, their presence cannot be used to determine where on the spectrum of digitalization an individual patient lies. For this purpose, careful observation of the patient and his electrocardiogram before and after a reduction or an increase in the dose of digitalis will usually provide the correct answer. When a more urgent need to know the state of digitalization exists, one may employ various diagnostic tests, such as carotid sinus stimulation or the acetyl strophanthidin test. When minor degrees of digitalis intoxication are present, the problem can be handled satisfactorily by cessation of the drug or by correction of any predisposing factors. This diagnosis must, nevertheless, be made promptly, since further administration of the drug may result in the onset of serious and, indeed, potentially lethal arrhythmias. When such arrhythmias occur, they can usually be managed quite effectively by potassium or procaine amide administration. The prevention of digitalis intoxication has been stressed particularly in elderly patients and in patients with severe myocardial disease. The use of the various glycosides based on their individual time of onset and maximum effectiveness the avoidance of parenteral administration and the appreciation of the limitations of these drugs are all important in the prevention of this disorder. Our purpose has been to review the diagnosis, prevention, and management of digitalis intoxication since an understanding of the potentially harmful effects of these drugs is crucial in order that digitalis may be given effectively and with confidence. Although intoxication may occur, digitalis, properly given, remains the most effective drug for the treatment of heart failure.