In two patients with old myocardial infarction and congestive heart failure there was a progressive reduction of heart rate variability and eventual sudden death. The two patients had had three 24 h electrocardiogram recordings within two years of death. The power of two spectral bands was calculated-0.04-0.15 Hz, low frequency power, and 0.15-0.40 Hz, high frequency power. The mean low and high frequency powers over the 24 h recording progressively decreased whereas the frequency of ventricular arrhythmias showed no consistent changes in either patient. The circadian variation in hourly low and high frequency powers in the last 24 h electrocardiogram recordings was much reduced. These results suggest that sequential measurements of heart rate variability may be useful in predicting sudden death.
The electrophysiological effects of verapamil (racemic compounds) and its optical (d- and 1-) isomers on canine ventricular myocardial fibers were investigated in current clamp conditions using single sucrose gap chamber and microelectrodes. The current-voltage (I-V) relationships were obtained in normal and low Na (12mM)-low Ca (0.45mM) solu-tions with and without the drugs. Verapamil and its optical isomers blocked repetitive action potential discharges (slow responses) induced by depolarizing DC-currents. However, 1-isomer was more potent than d-isomer in suppressing these responses. The difference in the potency was attributed to their different actions on the steady state I-V relationships. Namely, 1-isomer increased time independent membrane conductance to potassium ions (probably gkl), while d-isomer did not. This effect of 1-isomer may favor the suppression of phase 4 depolarization and hence reduce the frequency of repetitive action potential discharges in depolarized ventricular muscle more effectively than d-isomer.
It has not been determined if signal-averaged electrocardiograms (SAECGs) have a diurnal variation. We recorded 3-channel 24-hour ECGs in 30 healthy volunteers and calculated the following parameters for the first 500 sec of every hour over the 24-hour period: the mean heart rate, the filtered QRS duration (f-QRS), the root-mean-square voltage of the signals in the last 40 msec of the QRS (RMS40), and the duration of low-amplitude signals (< 40 microV) in the terminal portion of the QRS (LAS40). Heart rate and RMS40 increased in the daytime compared with the nighttime; f-QRS and LAS40 increased during the nighttime hours. The f-QRS and LAS40 were negatively correlated with heart rate in all and 22 (73%) of 30 subjects, respectively, and RMS40 was positively correlated with heart rate in 21 subjects (70%). In conclusion, SAECGs exhibit a clear diurnal variation in healthy subjects, which is closely related to changes in heart rate.
The case of a 64-year-old man with Wolff-Parkinson-White syndrome and permanent atrial fibrillation (AF) is reported. The patient was admitted due to electrocardiographic feature of AF with rapid conduction over the left-sided accessory pathway. Administration of pirmenol effectively suppressed the ventricular response via an accessory pathway. A transesophageal echocardiography detected an uncertain thrombus in the left atrial appendage. During the 33-month follow-up period, the ventricular response via an accessory pathway was progressively facilitated. Radiofrequency catheter ablation using a transseptal approach was performed during AF, resulting in complete elimination of the antegrade accessory pathway conduction.
Catheter ablation with the use of radiofrequency energy has been used as a treatment for atrioventricular reciprocating tachycardia in patients with Ebstein's anomaly. However, the success rate in these patients is generally low. We experienced a case in which the decision regarding precise accessory pathway (AP) localization was impaired by the presence of an abnormal electrogram in the atrialized right ventricle (ARV) in a patient with Ebstein's anomaly. After the AP conduction was abolished, the abnormal electrogram was observed behind the ventricular wave in the ARV during sinus rhythm. Furthermore, the interval between ventricular potential and the abnormal electrogram observed in the proximal ARV was longer than that in the distal ARV. We suggest that the abnormal electrogram might represent delayed local ventricular activation, and that the potential conduction might be impaired in the ARV.
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