Negative Chronotropic and Antidysrhythmic Effects of Hydroalcoholic Extract of Lemon Balm (Melissa Officinalis L.) on CaCl2-Induced Arrhythmias in Rats

BACKGROUND In many cases, myocardial infarction leads to arrhythmia. Since antioxidant agents have an important protective role in heart disease, these compounds in medicinal plants are used in traditional medicine. Lemon balm extract, compared to other plants of the lamiaceae family, has been proven to have significant amounts of antioxidant compounds. The aim of this study was to assess the effect of the hydroalcoholic extract of lemon balm (Melissa officinalis L.) on CaCl2-induced arrhythmias in rats. METHODS This research is an experimental study; male adult Sprague Dawley rats that weighed 200-250 g were divided randomly into three groups, i.e., 1) control (normal saline, 1 ml/kg/day), 2) extract (100 mg/kg), and 3) extract (200 mg/kg). The normal saline and the extracts were gavaged for 14 consecutive days. After anesthesia, lead II electrocardiograms were recorded for calculating the rats' heart rates (HRs). Arrhythmia was induced by intravenous injection of CaCl2 solution (140 mg/kg), and the percentages of incidence of ventricular tachycardia (VT), ventricular fibrillation (VF), and ventricular premature beats (VPB) were recorded. The results were analyzed by using Fisher's exact test and one-way ANOVA. P-values less than 0.05 were considered as significant level. RESULTS Heart rates and percentages of incidence of VPB, VT, and VF were reduced significantly in extract groups (with the highest activity at 200 mg/kg) in comparison with the control group. CONCLUSION Melissa officinalis was considered to be an antiarrhythmic agent because it reduced the percentage of incidence of VPB, VT, and VF in the groups that received it. The results indicated that Melissa officinalis had a protective effect on the heart.