CHRONIC EFFECT OF ORAL MEXILETINE ADMINISTRATION ON LEFT-VENTRICULAR CONTRACTILITY IN PATIENTS WITH CONGESTIVE-HEART-FAILURE - A STUDY BASED ON MITRAL REGURGITANT FLOW VELOCITY MEASURED BY CONTINUOUS-WAVE DOPPLER-ECHOCARDIOGRAPHY

The long-term effect of mexiletine on left ventricular (LV) contractility in patients with congestive heart failure is not clear. The authors therefore measured LV contractility before and after continuous oral administration of mexiletine in patients with congestive heart failure accompanied by mitral regurgitation (MR) using Doppler echorcardiography, The study population consisted of 8 patients with congestive heart failure (6 due to dilated cardiomyopathy and 2 due to old myocardial infarction) accompanied by significant functional MR who had more than 1000 ventricular premature contractions (VPCs) per day or Class IV Lown classification arrhythmias before mexiletine administration. The LV contractility was evaluated by calculating a Doppler-derived index, the rate of increase in LV pressure during the isovolumic contraction time (ICT (Delta P/Delta t), which has been confirmed to be nearly equal to LV Max dP/dt, The increase in LV pressure (Delta P) between 1 and 3 m/sec of the MR flow velocity as measured by continuous-wave Doppler echocardiography was calculated using the simplified Bernoulli's equation, and ICT Delta P/Delta t was derived by dividing Delta P by the time required for this change. The left ventricular ejection fraction and the left ventricular and left atrial dimensions also were measured by echocardiography, These parameters were obtained before and after 2 to 4 weeks of daily oral administration of mexiletine 300 mg. Values of ICT Delta P/Delta t were a 640 +/- 202 mm Hg/sec and 650 +/- 210 mm Hg/sec before and after mexiletine administration, respectively, showing no change, The left ventricular ejection fraction and the left ventricular and left atrial dimensions also were unchanged. These findings indicate that continuous oral administration of mexiletine has no effect on LV contractility in patients with congestive heart failure.