Electrophysiologic and blood-flow responses in the endocardium and epicardium to disopyramide and MS-551 during myocardial ischemia in the dog

Efficacy of nifekalant hydrochloride in the treatment of fatal ventricular arrhythmia in patients with ischemic heart disease

Ventricular tachycardia (VT), which causes hemodynamic instability, and ventricular fibrillation (VF) sometimes occur in patients with severe underlying cardiovascular disease such as myocardial ischemia or infarction, and are associated with high mortality. This report presents the efficacy of nifekalant hydrochloride (nifekalant), a pure class III antiarrhythmic agent, in treating life-threatening ventricular arrhythmia in such patients. From June 2000, when nifekalant became commercially available in Japan, to May 2003, 30 ischemic heart disease (IHD) patients with VT/VF resistant to direct-current (DC) countershock received nifekalant in our hospital. These 30 patients served as the nifekalant group in this study. As a control group, we also included 33 IHD patients with VT/VF that had been resistant to DC countershock upon or during hospitalization between January 1996 and May 2000 before nifekalant became commercially available. No significant differences were observed in patient background factors and treatments between the two groups. The rates of death within 48 hours of occurrence of VT/VF were significantly lower in the nifekalant group (7%, 2/30) than in the control group (27%, 9/33; P < 0.03). The rates of cardiac death during hospitalization were also significantly lower in the nifekalant group (40%, 12/30) than in the control group (67%, 22/33; P < 0.03). The rates of survival until hospital discharge were significantly higher in the nifekalant group (57%, 17/30) than in the control group (30%, 10/33; P < 0.03). Multivariate analysis of all 63 patients revealed nifekalant administration was the factor that significantly improved the mortality (odds ratio for cardiac death, 0.26; 95% confidence interval (CI), 0.07 to 0.95; P = 0.041). Nifekalant improves the prognosis for life-threatening ventricular arrhythmia in IHD patients.

Can Nifekalant Hydrochloride be Used as a First-Line Drug for Cardiopulmonary Arrest (CPA)?

BACKGROUND

Early defibrillation of ventricular tachycardia and fibrillation (VT/VF) is an urgent and most important method of resuscitation for survival in cardiopulmonary arrest (CPA). We have previously reported that nifekalant (NIF), a specific I(Kr) blocker developed in Japan, is effective for lidocaine (LID) resistant VT/VF in out-of-hospital CPA (OHCPA). However, little is known about the differences in the effect of NIF on OHCPA with acidosis and in-hospital CPA (IHCPA) without acidosis.

METHODS AND RESULTS

The present study enrolled 91 cases of DC shock resistant VT/VF among 892 cases of CPA that occurred between June 2000 and May 2003. NIF was used (0.15-0.3 mg/kg) after LID according to the cardiopulmonary resuscitation (CPR) algorithm of Tokai University. The defibrillation rate was higher in the NIF group for both OHCPA and IHCPA than for LID alone, and the VT/VF rate reduction effect could be maintained even with acidosis. However, sinus bradycardia in OHCPA, and torsades de pointes in IHCPA were occasionally observed. These differences in adverse effects might be related to the amount of epinephrine, serum potassium levels, serum pH, and interaction with LID.

CONCLUSIONS

NIF had a favorable defibrillating effect in both CPA groups, and it shows promise of becoming a first-line drug for CPR.

Nifekalant Hydrochloride Administration During Cardiopulmonary Resuscitation Improves the Transmural Dispersion of Myocardial Repolarization Experimental Study in a Canine Model of Cardiopulmonary Arrest

BACKGROUND

Because nifekalant hydrochloride (NIF) displayed a superior defibrillating effect on ventricular tachycardia/fibrillation (VT/VF) in cardiopulmonary arrest (CPA) patients, despite some QT prolongation, its effect on transmural dispersion of repolarization (TDR) in the left ventricle (LV) in an animal model of CPA was investigated.

METHODS AND RESULTS

Eight beagle dogs were created with a myocardial infarction under anesthesia, and then VT/VF induction by continuous stimulation and cardiopulmonary resuscitation (CPR) were repeated. NIF (0.3 mg/kg) was administered under acidotic conditions (pH 7.26). The QTc interval measured by Y-lead ECG showed no significant prolongation before and after NIF. The activation recovery interval (ARI) measured by 64-lead LV surface mapping showed minimum ARI prolongation (40%) by NIF without maximum ARI prolongation, and as a result the ARI dispersion decreased by 67%. The repolarization time (RPT) with the plunge electrode showed 13-19% prolongation in the subendocardium and subepicardium with CPR, but NIF prolonged the RPT in the middle layer alone (17%), and as a result Plunge-TDR decreased by 82% (n=8, p<0.05).

CONCLUSIONS

Administration of NIF during CPR decreased the TDR by RPT prolongation selectively in the middle layer. Because the subendocardial and subepicardial RPTs after CPR were already prolonged before NIF administration, it may have been the reason why the QT-prolonging effect of NIF was not reflected in the body surface ECG.

Effect of Nifekalant, a Class III Anti-Arrhythmic Agent, on Ca2+ Waves in Rat Intact Trabeculae

BACKGROUND

Nifekalant, a class III anti-arrhythmic agent, has been used clinically at serum concentrations of 1-10 micromol/L in patients with ventricular arrhythmias. However, the effect of nifekalant on triggered arrhythmias has not yet been established.

METHODS AND RESULTS

Trabeculae were dissected from the right ventricles of 16 rat hearts. The force was measured using a silicon strain gauge, the membrane potential using ultra-compliant microelectrodes, and the regional intracellular Ca2+ ([Ca2+]i) using electrophoretically microinjected fura-2 and an image intensified CCD camera at a sarcomere length of 2.1 microm. Rapid cooling contractures (RCCs) were measured to estimate the Ca2+ content in the sarcoplasmic reticulum. Ca2+ waves and aftercontractions were measured after the induction of reproducible Ca2+ waves. Nifekalant at 1, 10 and 250 micromol/L increased significantly the action potential duration, the peak [Ca2+]i, the developed force and the amplitude of RCCs in a concentration-dependent manner (stimulus interval = 2 s, [Ca2+]o = 0.7 mmol/L, 26.0+/-0.2 degrees C). Nifekalant at 10 and 250 micromol/L increased significantly the velocity of Ca2+ waves with an enhancement of the aftercontractions (stimulus interval = 0.5 s for 7.5 s, [Ca2+]o = 1.8+/-0.1 mmol/L, 22.3+/-0.5 degrees C).

CONCLUSIONS

Nifekalant, even at a therapeutic concentration, can increase muscle contraction, but may worsen triggered arrhythmias because of the acceleration of Ca2+ waves under Ca2+-overloaded conditions.