Heart, digitalis effects

Cardiac glycosides affect all excitable tissues, including smooth muscle and the central nervous system. The gastrointestinal tract is the most common site of digitalis toxicity outside the heart. The effects include anorexia, nausea, vomiting, and diarrhea. This toxicity is caused in part by direct effects on the gastrointestinal tract and in part by central nervous system actions. 

The distribution of cardiac glycosides in the plant varies in different species. Digitalis is obtained from the leaves and seeds strophanthus, from the seeds squill, from the bulbs Convallaria, from the flowers and ouabaio, from the wood and bark. In addition, there are saponin bodies that do not show the typical digitalis effect on the heart but which are extracted along with the glycosides, which possess the cardiac actions. 

Fig. 10. Chicago Heart Association Detection Project in Industry plasma glucose, other risk factors and myocardial infarction, ischemia, digitalis effect, current of injury, white males age 45-64 (29).

Digitalis Investigation Group (DIG) (1997) The effect of digoxin on mortality and morbidity in patients with heart failure. N Engl JMed 336 525-533... 

Cardiovascular manifestations include hypertension and cardiac arrhythmias (e.g., heart block, atrial flutter, paroxysmal atrial tachycardia, ventricular fibrillation, and digitalis-induced arrhythmias). In severe hypokalemia (serum concentration <2.5 mEq/L), ECG effects include ST-segment depression or flattening, T-wave inversion, and U-wave elevation. 

Ahmed A, Rich MW, Fleg JL, Zile MR, Young JB, Kitzman DW et al. Effects of digoxin on morbidity and mortality in diastolic heart failure the ancillary digitalis investigation group trial. Circulation 2006 114(5) 397-403. 

Phenytoin, like lidocaine, is more effective in the treatment of ventricular than supraventricular arrhythmias. It is particularly effective in treating ventricular arrhythmias associated with digitalis toxicity, acute myocardial infarction, open-heart surgery, anesthesia, cardiac catheterization, cardioversion, and angiographic studies. 

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