LOW MAGNESIUM ENHANCES THE PROARRHYTHMIC EFFECT OF LOW POTASSIUM IN THE HYPERTROPHIED RAT-HEART BUT NOT IN THE NORMAL RAT-HEART

Objectives To investigate the influence of external magnesium on wall stress-induced arrhythmias and to establish whether early cardiac hype rtrophy affects the sensitivity of the heart to these arrhythmias. Met hods We used a modified isolated working heart model to compare hypert rophied hearts from the spontaneously hypertensive rat (SHR) with hear ts from normotensive control rats from the Wistar and Wistar-Kyoto str ains, Young rats (aged 137.9 +/- 2.04 days mean +/- SEM) were used to ensure left ventricular hypertrophy uncomplicated by fibrosis and card iac failure, Arrhythmias were induced by 20 s increases in ventricular afterload during which the electrocardiogram was recorded. Results In control experiments SHR hearts showed a significantly greater arrhyth mic response than did normotensive control rat hearts during perfusion with low-potassium (2.4 mmol/l) solutions. Concomitant low magnesium (0.4 mmol/l) perfusion significantly increased the arrhythmic response to 2.4 mmol/l potassium in SHR hearts but had no effect on arrhythmia s in normotensive control rat hearts. With low magnesium, the number o f ventricular premature beats was increased in SHR hearts compared wit h that in normotensive control rat hearts during perfusion with 4.2 an d 2.4 mmol/l potassium. In addition, perfusion with low magnesium and 2.4 mmol/l potassium led to an increase in the complexity of arrhythmi as, ventricular tachycardia occurring in nine of 10 SHR hearts but in only two of six normotensive control rat hearts. Conclusions There is a synergistic effect of low magnesium and low potassium on wall-stress -induced arrhythmia in the SHR heart An analogous effect might be impo rtant in patients with hypertension and left ventricular hypertrophy, in whom systolic blood pressure is frequently labile, leading to wide fluctuations in ventricular wall stress; combined potassium and magnes ium depletion is a common complication of antihypertensive treatment.