T wave alternans for predicting adverse effects of amiodarone in a patient with dilated cardiomyopathy.

An implantable cardioverter defibrillator (ICD) was used in a 62-year-old man with dilated cardiomyopathy (DCM) because of hemodynamically intolerable ventricular tachycardia (VT). Amiodarone was administered after a second episode of ICD discharge. Three weeks later, incessant VT appeared, and DC discharge failed to terminate it. Microvolt T wave alternans (TWA), measured by a spectral method, was observed in this patient with and without amiodarone administration. The onset heart rate with TWA was lower and the alternans voltage was higher with amiodarone than without it. The effects of amiodarone appeared to be related to the exacerbation of VT and an increased defibrillation threshold. TWA might be useful in predicting the proarrhythmic effects of amiodarone in similar cases.

Ventricular arrhythmias with left bundle branch block pattern and inferior axis: assessment of their mechanisms on the basis of response to ATP, nicorandil and verapamil.

The present study investigated the mechanism of ventricular arrhythmias showing left bundle branch block (LBBB) pattern with an inferior axis. The effects of 3 drugs, adenosine triphosphate (ATP), nicorandil and verapamil, were evaluated in 17 patients. ATP suppressed the arrhythmias in 14 patients and nicorandil suppressed them in 8 of those 14. Verapamil suppressed 5 of the 6 ATP-nicorandil-sensitive arrhythmias. Four patients with ATP- or nicorandil-sensitive arrhythmias were not sensitive to verapamil. On the other hand, 3 of the ATP-insensitive arrhythmias were sensitive to neither nicorandil nor verapamil. The QT intervals and QTc were shortened by nicorandil in 5 of the 6 patients who were sensitive to all 3 drugs. One mechanism of suppression by nicorandil could be related to less Ca++ entering the myocardium, which would decrease the duration of the action potential as indicated by the shortened QT intervals. The results suggest that the mechanism of some ventricular arrhythmias is related to triggered activity. Arrhythmias that are sensitive to ATP or nicorandil, but not to verapamil, may be caused by abnormal automaticity. On the other hand, arrhythmias that are insensitive to all 3 drugs might be related to reentry. The features of ventricular arrhythmias with LBBB pattern and inferior axis differ and therefore the causative mechanisms are not the same.

Neurally mediated syncope and arrhythmias: a study of syncopal patients using the head-up tilt test.

Understanding the causes of syncope in patients with arrhythmia is important in determining the therapeutic interventions. Neurally mediated syncope (NMS) was evaluated in 55 patients with various arrhythmias. The head-up tilt test with or without isoproterenol infusion induced NMS in 41 (74%) patients. When these patients was categorized into 3 types, depending on the development of syncope, vasodilatation was significant in a majority of patients. In 46% of patients with tachyarrythmias, NMS was accompanied by an increase in extrasystole. It was concluded that the evaluation of vasodilatation is important for the preventive strategy of NMS in patients with arrhythmias and that NMS may induce arrhythmias.

Long-term effects of pharmacological therapy for vasovagal syncope on the basis of reproducibility during head-up tilt testing.

The purpose of this study was to determine the efficacy of long-term pharmacological therapy selected on the basis of a head-up tilt test (HUT) in patients in whom reproducibility of the HUT response was demonstrable in the initial study. The HUT (80 degrees upright) was performed for 15 min with or without an infusion of isoproterenol (0.01-0.03 microgram/kg per min) in 54 patients with recurrent unexplained syncope. When vasovagal syncope was induced (positive response), the HUT was repeated to examine the test reproducibility. Vasovagal syncope was induced in 24 patients during HUT alone, and in 30 patients during the HUT with isoproterenol. Acute reproducibility was observed in 49/54 (91%) patients. In the tilt-positive patients, HUT was repeated after an intravenous administration of propranolol (0.1 mg/kg) or disopyramide (1 mg/kg) (acute test). Propranolol proved effective in 21 (80%) of 26 patients, and disopyramide in 13 (56%) of 23 patients. Thereafter, evaluation was done on the long-term clinical follow-up of the pharmacological intervention selected on the basis of the acute test in the 34 patients in whom the HUT could not induce vasovagal syncope after the oral administration of the pharmacological agent (propranolol 60 mg/day, disopyramide 300 mg/day). Thirty-two of 34 patients (94%) did not develop syncopal attacks during a 44 +/- 12-month period. Thus, in patients with unexplained syncope, HUT appears to have a high degree of acute reproducibility, and the acute drug response guided by HUT may be used to develop an effective long-term pharmacological therapy.