ECG-CHANGES UNDER HYPERKALEMIA WITH NEPHRECTOMY IN THE RAT

Electrolyte abnormalities have become an increasingly important cause of arrhythmias. Although the electrocardiographic (ECG) changes under hyperkalemia in the rat are poorly understood, it is conceivable that excess plasma potassium may also alter the cardiac excitations in the rat. Further, effects of hyperkalemia on ECG in the rat may differ from other species that have ST-segment and longer QT intervals in ECG. The present study was designed to determine the diagnostic criteria for ECG manifestations to various levels of plasma potassium concentration. For this purpose, hyperkalemia was induced by nephrectomy with and without infusions. Because it was difficult to produce various levels of plasma potassium concentration by only nephrectomy, we used two kinds of infusions to obtain especially moderate levels of nephrectomy-induced hyperkalemia. ECGs were recorded 24, 36, and 48 hours after nephrectomy. Plasma potassium concentration and number of abnormal ECGs were increased time-dependently. Increased T wave amplitude was present with mild hyperkalemia. The typical T wave change observed with so-called sinoventricular conduction levels of potassium concentration in species with long QT intervals did not occur in the rat. PR interval and QRS duration became slightly shorter within moderate hyperkalemia. P wave disappeared in most rats at potassium levels above 8.0 mEq/l. In advanced hyperkalemia (plasma potassium concentration above 7.5 mEq/l), conduction in all parts of the heart was suppressed. Moreover, sinoventricular conduction appeared. Thus, the diagnostic criteria for ECG manifestations to various levels of plasma potassium concentration in the rat were demonstrated. Although the typical T wave changes as seen in species with ST-segment type ECGs were absent in the rat, other changes in ECG parameters with hyperkalemia in the rat were qualitatively similar in other species. These results may be useful for studying electrolyte abnormalities and/or testing the toxicity of drugs in the rat.