| AGENT | MECHANISM
| ECG CHANGES |
| Penicillin | Rapid IV administration of the potassium salt may produce ECG changes characteristic of hyperkalemia; anaphylactic reactions also may produce a variety of ECG changes
| See hyperkalemia; prominent T waves and marked QT prolongation; ST segment changes, atrial fibrillation; junctional rhythm
|
| Pentamidine | Structurally similar to procainamide; binds avidly to cardiac tissue, which may produce ECG changes after discontinuation of therapy
| QTc prolongation with associated torsade de pointes; T wave abnormalities and ST segment changes
|
| Erythromycin | Metabolic alterations occurring in ischemia or after digitalis administration may enhance the loss of potassium
| QT prolongation |
| Quinine | Quinine is the l-isomer of quinidine; the cardiovascular effect of quinine is estimated at1/3 that of quinidine
| PR prolongation, QRS widening, QT prolongation, prominent U waves; overdose can cause asystole and ventricular tachycardia including torsade de pointes
|
| Amantadine | Chemical structure and pharmacologic properties are similar to TCAs: hypotension, bradycardia, and arrhythmias
| Sinus tachycardia, PR, QRS, and QT prolongation, ectopic activity. Cardiac arrest, including ventricular tachycardia and torsade de pointes, may appear as long as 36 hours after ingestion of toxic doses
|
| Doxorubicin | Dose-dependent irreversible cardiomyopathy may be due to free radical formation with release of cardiac histamine and other vasoactive substances; may also directly affect calcium ion channels, producing irreversible cell damage due to intracellular calcium overload
| Acute: supraventricular arrhythmias (rarely clinically significant); chronic: decreased QRS voltage
|
| Lithium | Artial displacement of intracellular potassium sinus node dysfunction with bradycardia
| T wave abnormalities; first degree AV block, paroxysmal left bundle branch block; at toxic doses, may see QTc prolongation
|
| TCAs | Possess anticholinergic activity, exert a direct myocardial depressant activity, and block noradrenaline reuptake in the heart
| Similar to those produced by the phenothiazines and class I antiarrhythmics: increased heart rate, prolongation of the PR interval, intraventricular conduction disturbances, increase in QTc interval, and flattening of T waves
|
| Carbamazepine | Shortens action potential duration
| Sinus bradycardia, AV conduction disturbances may occur with therapeutic or modestly elevated plasma concentrations; tachycardia occurs in overdose; older patients or those with pre-existing conduction abnormalities are particularly vulnerable
|
| Probucol | Unknown mechanism
| Reversible prolongation of QTc interval; Probucol is eliminated slowly, so abnormality may persist after discontinuation of therapy
|
| Cotrimoxazole | Unknown mechanism
| QT prolongation |
