No abstract

In magnetocardiographic (MCG) localization of arrhythmia substrates, a model of the thorax as volume conductor is a crucial component of the calculations. In this study, we investigated different models of the thorax, to determine the most suitable to use in the computations. Our methods and results are as follows. We studied 11 patients with overt Wolff-Parkinson-White syndrome, scheduled for catheter ablation. The MCG registrations were made with a 37-channel "superconducting quantum interference device" system. The underlying equivalent current dipole was computed for the delta-wave. Three models of the thorax were used: the infinite halfspace, a sphere and a box. For anatomical correlation and to define the suitable sphere and box, magnetic resonance images were obtained. As reference we used the position of the tip of the catheter, at successful radio-frequency-ablation, documented by cine-fluoroscopy. Nine patients could be evaluated. The mean errors (range) when using the infinite halfspace, the sphere and the box were 96 (49-125), 21 (5-39), and 36 mm (20-58 mm), respectively (p < 0.0001). In conclusion, the sphere was significantly better suited than the other models tested in this study, but even with this model the accuracy of MCG localization must further improve to be clinically useful. More realistic models of the thorax are probably required to achieve this goal.

Objective-To study the value of intravenous disopyramide as part of an invasive electrophysiological study in predicting impending high degree atrioventricular block in patients with bifascicular block. Design-An invasive electrophysiological study was performed in the basal state and after the infusion of disopyramide (2 mg/kg body weight). The progression to high degree atrioventricular block was assessed by bradycardia-detecting pacemakers or repeated 12-lead electrocardiogram recordings, or both. Patients-73 patients with bifascicular block were included, of whom 25 had a history of unexplained syncope. The remaining 48 patients had no arrhythmia related symptoms and were included as controls. All patients had an ejection fraction of > 35%. Results-After a mean follow up of 23 months, seven patients in the syncope group and three in the non-syncope group had a documented high degree atrioventricular block or pacemaker-detected bradycardia of < 30 beatsimin for > 6 s. The sensitivity of the disopyramide test was 71% and the specificity 98%. The corresponding figures for an abnormal electrophysiological study in the basal state were 14% and 91%, respectively. Conclusions-The sensitivity of an invasive electrophysiological study in patients with bifascicular block and syncope can be markedly increased by the use of intravenous disopyramide. A positive test is a highly specific finding and warrants pacemaker implantation. (Br Heart J 1995;74:650-655) Keywords: disopyramide stress test, atrioventricular block, bifascicular block, electrophysiological study Bifascicular block, defined as left bundle branch block or right bundle branch block with left anterior or posterior fascicular block, has a prevalence of between 1% and 1-5% in an adult population.'-3 Up to 25% of patients with bifascicular block have a history of syncope3 and the management of these patients is a common clinical problem. The overall yearly incidence of progression to high degree atrioventricular block is only 1-4%3-5 and the strategy of pacemaker implantation in all symptomatic patients can thus be questioned. No non-invasive test has been found to be useful in predicting subsequent high degree atrioventricular block, and an invasive electrophysiological study is often of limited value.47 Findings with a high specificity, such as an HV interval of > 100 ms and a His-Purkinje block during atrial pacing, are rare and hence have a low sensitivity.5 8In order to increase the sensitivity of an electrophysiological study, a pharmacological stress test of the His-Purkinje system has been proposed, and ajmaline,9 10 procainamide,"-13 and disopyramide'4 '5 have been used for this purpose. The clinical value of these tests has, however, not been well defined, primarily because of the lack of appropriate controls and the lack of sensitive tools for detecting intermittent high degree atrioventricular block.The aim of this study was to evaluate prospectively the value of intravenous disopyramide as part of an invasive electrophysiological study...

Survival in patients paced for high degree AV block has been demonstrated to be influenced by underlying cardiac disease in particular congestive heart failure. One previous study has suggested that dual chamber pacing may improve the vital prognosis for such patients. To investigate this, 74 patients treated with rate adaptive atrial synchronous (VDD) and 74 patients treated with VVI pacemakers for high degree AV block, were retrospectively studied for a mean of 5.4 years by life-table analysis. The two groups had an equal distribution of age, sex, date of pacemaker implantation, and concomitant cardiovascular diseases. Total mortality and estimated survival did not differ between the two groups. The estimated survival in the VDD group at 1, 3, and 5 years for patients without and with congestive heart failure was 94%, 86% and 78%, and 92%, 83% and 72%, respectively. In the VVI group the corresponding values were 95%, 90%, and 83% for patients without congestive heart failure and 82%, 64%, and 47% for those with congestive heart failure (P = 0.008). Compared to the expected survival rate of the general Swedish population, only the VVI group with congestive heart failure, had an excess mortality (P = 0.007). Patients with high degree AV block have a fairly normal vital prognosis irrespective of pacing mode. The prognosis for patients with congestive heart failure was negatively affected by VVI pacing. Thus, for patients with congestive heart failure the choice of pacing mode is of vital importance, whereas for patients without congestive heart failure, other factors such as feeling of well-being and exercise capacity should decide the final choice of pacing mode.

Objectives. To evaluate the duration of anticoagulation treatment with warfarin sodium before elective DC-cardioversion and to identify clinical variables predicting short-term versus long-term waiting times. Design. Retrospective. Subjects. Patients with a known start date for warfarin sodium, a known duration of atrial fibrillation (AF) and who underwent DC-cardioversion were included. Main outcome measures. Duration of treatment with warfarin sodium prior to DC-cardioversion. Methods. The hospital records of 288 consecutive patients with AF scheduled for elective cardioversion at two hospitals in Stockholm were reviewed. Only patients with a known start date for warfarin sodium and known duration of AF were included in the study.Results. The median age was 70 (26-85) years and the duration of AF at time of cardioversion were 18 weeks (5-273) weeks. The median treatment duration prior to cardioversion with warfarin sodium was 12 weeks. Sinus rhythm was established in 224 (78%) patients of which 90 (40%) remained in sinus rhythm 1 month after cardioversion. In multivariate analysis, the only independent predictor of short waiting times for cardioversion (8 vs. 15 weeks) was if a cardiologist instituted the treatment with warfarin sodium (P < 0.001, 95% CI 5.0-9.0). Conclusion. The average waiting time from start of warfarin sodium treatment to elective cardioversion exceeds by far the recommended 3-4 weeks on therapeutic international normalized ratio (INR). In order to minimize the time period until cardioversion significant changes in the out-of-hospital care logistics has to be undertaken.