תוצאת חיפוש

Circadian Fluctuations of the Signal-Averaged ECG

Ehud Goldhammer, Edward Abinader

Cardiology Dept., Bnei-Zion Medical Center and Bruce Rappaport Faculty of Medicine, The Technion, Haifa

Circadian periodicity for the time of onset of acute myocardial infarction has been shown; the early morning peak of infarction coincides with the onset of other related phenomena, including sudden cardiac death, ventricular arrhythmias, thrombotic stroke, etc. Late potentials detected by the signal-averaged ECG are considered to be independent markers of vulnerability to ventricular arrhythmias. The signal-averaged ECG enables the amplifying and recording of small bioelectric signals of cardiac origin, while eliminating extraneous electrical "noise." To determine whether late potentials are themselves subject to circadian influence, 31 patients (age range 41-79) who had had an old or recent myocardial infarction underwent late potential assessment by the signal-averaged ECG. 4 indices were studied: duration of late LPD potentials (LPD), total QRS duration (TQRS), and root mean square voltage of the last 40 msec, and of the last 50 msec (RMS 40 and RMS 50). These indices were assessed 3 times, during the early morning hours, at noon and during the evening. Morning LPD differed significantly from noon and evening LPD and the morning RMS 40 similarly differed from noon and evening values. TQRS and RMS 50, even though remaining in the normal range, also showed a tendency to abnormal values during morning hours. These findings could possibly be related to the early morning incidence peaks of severe ventricular arrhythmia and sudden cardiac death, since abnormal late potentials constitute the physiopathological basis for certain ventricular arrhythmias.

Effect of Chlorocresol VS Caffeine on Muscle Contracture in Malignant Hyperthermia Susceptible Patients

R. Ben-Abraham, R.M. Krivosic-Horber, G. Haudcoeur, A. Perel, P.J. Adnet

Dept. of Anesthesiology and Intensive Care, Chaim Sheba Medical Center, Tel Hashomer and Sackler Faculty of Medicine, Tel Aviv University; and Dept. d'Anesthesie-Reanimation Chirurgicale, Laboratoire de Pharmacologie Hospitaliere, et Service des Urgence, Centre Hospitalier Universitaire, Lille Cedex, France

The phenotype of susceptibility to malignant hyperthermia (MHS); can only be detected reliably by the in vitro caffeine-halothane contracture test (CHCT). Enhanced sensitivity of the calcium-induced calcium release mechanism is responsible for the exaggerated contracture response of skeletal muscle fibers from MHS patients to halothane and caffeine. Chlorocresol was demonstrated to be a potent activator of Ca++release from skeletal muscle sarcoplasmic reticulum. This effect is probably mediated through action on a ryanodine sensitive Ca++ release channel known to be more sensitive in MH. We studied the effect of chloroscresol on the mechanical contracture response of skeletal muscle from patients presenting for the in vitro CHCT. Chlorocresol induces contracture response in a concentration 1/200 of that of caffeine in muscle strips from MH patients. By adding chlorocresol to the protocol of the CHCT, there is clearer discrimination between the responses of MH patients and normal subjects can be achieved.