Ryuta Imaki

Mexiletine protects myocardium during acute ischemia by opening sarcolemmal K-ATP channel: studies in closed-chest acute ischemia model in rabbits.

Objectives: Although we have previously shown that mexiletine might protect myocardium during acute ischemia, the precise mechanism was unclear. In the present study, the mechanism of this effect was examined by using selective K-ATP channel blockers in closed-chest acute ischemia model in rabbits. Methods: In 40 rabbits, the large left ventricular branch (LLVB) of the left coronary artery was occluded for 30 minutes by inserting a catheter bead (ϕ0.5-0.7 × 1.5 mm) through the left carotid artery and was then reperfused. The rabbits were divided into the following 5 groups: (1) control group (n = 8); (2) mexiletine (Mex) group (n = 8, continuous infusion of Mex 24 mg/kg/h); (3) Mex + 5-hydroxydecanoate (5HD) group (n = 8, preadministration of 5HD, 5 mg/kg, followed by Mex infusion); (4) Mex + HMR1098 (selective sarcolemmal K-ATP channel blocker) group (n = 8, preadministration of HMR1098, 3 mg/kg, followed by Mex infusion); and (5) pilsicainide (Pil) group (n = 8, continuous infusion of Pil 18 mg/kg/h). The incidence of ventricular arrhythmia, hemodynamics, left ventricular ejection fraction (LVEF), and infarction size were evaluated and compared among the 5 groups. Results: The incidence of ventricular arrhythmia was lower in groups treated with Mex than the control. The hemodynamics did not show significant differences among the 5 groups. Although the LVEF at 30 minutes after reperfusion was lower in the Mex group (41 ± 3%, P < 0.001) than the control group (48 ± 3%), the LVEF at 360 minutes after reperfusion had recovered and became higher in the Mex group (62 ± 3%, P < 0.001) than the control group (55 ± 3%). The infarction size was smaller in the Mex group (30 ± 5%, P = 0.028) than the control group (51 ± 8%). These effects of Mex were negated by HMR1098 but not by 5HD and were larger than the effects of Pil. Conclusions: Mex showed improvement in the LVEF in the later phase after reperfusion as well as a reduction in ventricular arrhythmia. The cardioprotective effect of Mex was considered to appear through its action on the sarcolemmal K-ATP channel.

Usefulness of ST elevation score by using vector-projected virtual 187-channel ECG for risk stratification in patients with Brugada-type ECG pattern

Although powerful defibrillation devices are available in clinical practice, risk stratification is important in asymptomatic Brugada syndrome. In this study, vector‐projected 187‐channel electrocardiogram (VP‐ECG) was used to calculate the ST‐elevation score in Brugada‐type ECG and test its usefulness in risk stratification.

Preventive Effect of Amiodarone on VT/VF Events in ICD Patients with Structural Heart Diseases

Background: Although amiodarone (AMD) is applied for implantable cardioverterdefibrillator (ICD) patients to reduce VT/VF events, its actual benefit and long‐term efficacy are unclear. In the present study, we retrospectively evaluated the incidence of VT/VF events in ICD patients with and without AMD.

Effect of nifekalant on life-threatening ventricular arrhythmias in patients with cardiopulmonary resuscitation or during the perioperative state

Background: Nifekalant is a unique class III anti‐arrhythmic agent with a strong effect on prolonging the myocardial refractoriness, but its clinical effect is still unclear. In this study, we evaluated the effect of nifekalant on life‐threatening ventricular arrhythmias and compared the clinical background between the effective and non‐effective patients in order to clarify the clinical factors which may have an influence on the efficacy of nifekalant.

Morphological Properties of Atrial Fibrillation Waves in Patients with Left Ventricular Dysfunction —Spectral Analysis of Atrial Fibrillation Waves in Dilated Cardiomyopathy—

Introduction: Although the atrial fibrillation cycle length (FCL) is considered to shorten in persistent atrial fibrillation (AF) as a result of electrical remodeling, whether a long‐term change remains in FCL in patients with left ventricular (LV) dysfunction is uncertain. Morphological properties of AF waves were analyzed in patients with dilated cardiomyopathy (DCM). Methods and Results: The study population consisted of 43 patients with persistent AF, and they were divided into a DCM group (n = 14) and a control group (n = 29). Fibrillation waves from surface ECG lead V1 were purified by subtracting the QRS‐T complex template. Power spectral analysis was performed by Fast Fourier Transformation, and the mean FCL was determined by the peak power frequency in 20 epochs at each recording. The LV ejection fraction was lower in the DCM group (50 ± 18%) than the control (63 ± 8%, p = 0.001). The mean FCL was shorter in the DCM group (132 ± 14 ms) than the control (151 ± 23 ms, p = 0.007) and there was a significant correlation between the FCL and LV dimensions (p = 0.03). Conclusion: In patients with persistent AF and LV dysfunction, FCL was shorter in comparison with the control, and seemed to be influenced by LV dimensions.