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Notes: Ventricular Dilatation and d,l-Sotalol/Flecainide in Isolated Rabbit Heart. Introduction: The interaction between acute ventricular dilatation (AVD) as one aspect of ventricular dysfunction and Class I and III antiarrhythmic drugs is uncertain. We therefore investigated the effects of AVD on the electrophysiologic properties of d,l-sotalol and flecainide. Methods and Results: The isolated rabbit heart was used as a model of AVD. The ventricular size and, therefore, the diastolic pressure were modified by sudden volume changes of a fluid-filled balloon placed in the left ventricle. Pacing was performed alternately using epi- and endocardial monophasic action potential (MAP)-pacing catheters at cycle lengths from 1,000 to 300 msec. d,l-Sotalol (10 μM) resulted in a significant (P 〈 0.05) lengthening of refractoriness (+13.5%± 3.1%), MAP duration (+14.9%± 3.2%), and QT interval (+15.5%± 4.1%) (mean ± SEM at 1,000 msec). These effects had a reverse rate-dependence. AVD to a diastolic pressure of 30 mmHg reduced refractoriness and left ventricular MAP duration. In comparison with the control group with the same extent of WD, d,l-sotalol still led to a significant prolongation of repolarization for all cycle lengths except 300 msec, so that its effects were not absolutely but relatively preserved. In contrast, flecainide (2μM) had no significant effects on refractoriness or MAP duration. It led to a significant, rate-dependent increase of pacing thresholds (+47.6%± 8.2%), prolongation of QRS (+48.8%± 5.6%), and conduction time (+78.6%± 8.6%) (mean ± SEM at 300 msec). In the flecainide group, AVD significantly increased the normal rate-dependent prolongation of QRS (+16.7%± 5.5%) and conduction time (+17.1%± 4.3%). Conclusion: Our data demonstrate that, during AVD, the Class III effect of d,l-sotalol is preserved, whereas flecainide's effect of slowing conduction is exaggerated. This may contribute to flecainide-related proarrhythmia in certain clinical situations.

Notes: Effect of Transvenous Electrode Polarity on DFT. Introduction: The defibrillation threshold (DFT) of a transvenous-subcutaneous electrode configuration is sometimes unacceptably high. To obtain a DFT with a sufficient safety margin, the defibrillation field can be modified by repositioning the electrodes or more easily by a change of electrode polarity. In a prospective randomized cross-over study, the effect of transvenous electrode polarity on DFT was evaluated. Methods and Results: In 21 patients receiving transvenous-subcutaneous defibrillation leads, the DFT was determined intraoperatively for two electrode configurations. Two monophasic defibrillation pulses were delivered in sequential mode between either the right ventricular (RV) electrode as common cathode and the superior vena cava (SVC) and subcutaneous electrodes as anodes (configuration I) or the SVC electrode as common cathode and the RV and subcutaneous electrodes as anodes (configuration II). In each patient, both electrode configurations were used alternately with declining energies (25, 15, 10, 5, 2 J) until failure of defibrillation occurred. The DFT did not differ between both configurations (18.3 ± 8.2 J vs 18.9 ± 8.9 J; P = 0.72). Eleven patients had the same DFT with both electrode configurations, 5 patients a lower DFT with the RV electrode as cathode, and 5 patients a lower DFT with the SVC as cathode. Four patients had a sufficiently low DFT (≤ 25 J) with only 1 of the 2 configurations. Conclusion: A change of electrode polarity of transvenous-subcutaneous defibrillation electrodes may result in effective defibrillation if the first electrode polarity tested fails to defibrillate. In general, neither the RV electrode nor the SVC electrode is superior if used as a common cathode in combination with a subcutaneous anodal chest patch.

Notes: Variants of Preexcitation. introduction: In the present report, the electrophysiiologic findings in patients with different types of variants of preeexcitwtion, i.e., atriofascicualr, nodofacicular, and fasciculoventricular fibers, and the results of radiofrequency catheter ablation using different target sites are described. Methods and Results: Twelve patients (mean age 36 ± 17 years) with variants of the preexcitation syndromes underwent electrophysiologic study and radiofrequency catheter ablation. The atrial origin of atriofascicular pathways remote from the normal AV node was assessed by application of late atrial extrastimuli that advanced (“reset”) the timing of the next QRS complex without anterograde penetration into the AV node. In patients with atriofacicular pathways, ablation of the accessory pathway or the retrograde fast AV node pathway was attempted. Ablation of the atriofascicular pathways was guided by a stimulus-delta wave interval mapping in the first live patients and by recording of atriofascicular pathway activation potentials in the next five patients. A nodofascicular pathway was suggested if VA dissociation occurred during tachycardia and if atrial extrastimuli failed to reset the tachycardia without anterograde penetration into the AV node. A fasciculoventricular connection was suggested if the proximal insertion of the accessory pathway was found to arise from the His bundle or bundle branches. The PR interval was expected within normal limits during sinus rhythm and the QRS complex to he slightly prolonged with a discrete slurring of the R wave, suggesting a small delta wave. Ten of the 12 patients had evidence for atriofascicular pathways and one patient each for a nodofascicular and fasciculoventricular pathway. In six patients, the atriofascicular pathways were successfully ablated, and in two patients, the retrograde fast AV node pathway. In one patient, a concealed right posteroseptal accessory AV pathway served as the retrograde limb and was successfully ablated. The nodofascicular pathway was shown to he a bystander during AV node reentrant tachycardia. After successful fast AV node pathway ablation resulting in marked PR prolongation, no preexcitation was present during sinus rhythm because of the proximal insertion of the nodofascicular pathway distal to the delay producing parts of the AV node. The proximal insertion of the fasciculoventricular pathway was suggested to arise distal to the AV node at the site of the penetrating AV bundle. The earliest ventricular activation at the His-bundle recording site indicated the ventricular insertion of this accessory connection into the ventricular summit. The fasciculoventricular connection gave rise to a fixed ventricular preexcitation and served as a bystander during orthodromic AV reentrant tachycardia incorporating a left-sided accessory AV pathway.

Notes: Late Potentials in CAD. In patients who have survived acute myocardial infarction, thepresence of ventricular late potentials using the high resolution signal-averaged KCG indicatesareas of slow conduction and delayed activation that may potentially serve as a substrate lormalignant ventricular arrhythmias. Although detection of late potentials is technique specific, signal-averaged analysis in the time or frequency domain may he a useful index for riskstratification with regard to ventricular tachycardia or sudden cardiac death. The sensitivityand specificity of late potentials for this purpose may he enhanced by comhination with othervariables, such as left ventricular ejection fraction and presence of complex ventricular ectopy, Therefore, the presence of ventricular late potentials in postmyocardial infarction patients, particularly in those patients with impaired left ventricular function, identifies those patienlswho are at high risk of malignant ventricular tachyarrhythmias, However., (he strategies forprevention of serious arrhythmia complications during follow-up need to be established, Thenegative predictive value of late potentials is very high. Thus, the absence of late potentialsindicates a low propensity to sustained ventricular tachycardia or sudden death, even in thepresence of complex ventricular ectopy. Interventions may therefore not be necessary orshould even he avoided, The incidence of late potentials in patients with spontaneous orinduced ventricular fibrillation is lower and, if present, less pronounced than in those with sustained monomorphic ventricular tachycardia. This presumably is due to a lower degree of conduction delay, which serves as a substrate for reentry. Therefore, the ability of the signal-aver-aged ECG to predict a propensity to ventricular fibrillation is limited, Despite these limitations, the signal-averaged ECG may be used as a risk predictor in evaluation of patients aftermyocardial infarction. Unfortunately, at least as far as time domain analysis is concerned, itcannot be used as an efficacy predictor for response to pbarniacologic interventions, Furtherstudies will determine whether other modes of signal-averaged analysis can predict theresponse to drugs.

Notes: Biphasic Defibrillation with Nonthoracotomy Leads. Introduction: For current implantable defibrillators, the nonthoracotomy approach to implantation fails in a substantial number of patients. In a prospective randomized cross-over study the defibrillation efficacy of a standard monophasic and a new biphasic waveform was compared for different lead configurations. Methods and Results: Intraoperatively, in 79 patients receiving nonthoracotomy defibrillation leads, the defibrillation threshold was determined in the initial lead configuration for the mono-and biphasic waveform. In each patient, both waveforms were used alternately with declining energies (20, 15,10, 5 J) until failure of defibrillation occurred. Three different initial lead configurations were tested in different, consecutive, nonrandomized patients using a bipolar endocardial defibrillation lead alone (A; n = 36) or in combination with a subcutaneous defibrillation patch (B; n = 24) or array (C; n = 19) lead. The lowest successful defibrillation energy with the biphasic waveform was less than, equal to, or higher than with the monophasic waveform in 64%, 28%, and 8% of patients, respectively, and on average significantly lower with the biphasic waveform for all three lead configurations (A: 11.3 ± 4.4 J vs 14.5 ± 4.5.); B: 9.7 ± 4.7 J vs 15.1 ± 4.5 J; C: 7.9 ± 4.5 J vs 12.4 ± 4.9 J). Defibrillation efficacy at 20 J was significantly improved by the biphasic waveform (91% vs 76%). Conclusion: In combination with nonthoracotomy defibrillation leads, the biphasic waveform of a new implantable cardioverter defibrillator showed superior defibrillation efficacy in comparison to the standard monophasic waveform. Defibrillation thresholds were improved for lead systems with and without a subcutaneous patch or array lead.