The Clinical Incidence and Significance of Myopotential Sensing with Unipolar Pacemakers

Myopotential oversensing by unipolar pulse generators can cause patient symptoms ranging from dizziness and syncope to ventricular tachycardia. Seventy-seven patients with implanted unipolar pacemakers from three manufacturers participated in isometric and reach exercises to evaluate their pacemakers susceptibility to myopotentials. Myopotential inhibition occurred in 47% of the patients performing the reach maneuver. Testing revealed a wide difference in level of susceptibility to myopotentials between pacemakers of different manufacture (a low of 33% inhibition for the least susceptible to a high of 78% inhibition for the most susceptible during the reach maneuver). The normal pacing interval was extended by myopotential oversensing for each manufacturer's model within a range of 0.3–3.9 seconds. Pulse generators incorporating additional automatically-adjusting threshold and reversion circuits in the sense amplifier along with standard bandpass filtering exhibited: a) two-to-three times less susceptibility to myopotentials; and b) a 75% reduction in the maximum pacing interval extension as compared with pacemakers with bandpass filtering alone. The effectiveness of insulative coating in reducing myopotential inhibition was substantiated as coated pulse generators had a 22% lower incidence of muscle sensing than those than were uncoated. Six out of seven patients tested had symptoms during Holter monitoring which correlated with pacemaker myopotential inhibition. Selecting pulse generators with improved sensing amplifiers, clinical testing of patients with unipolar pacemakers using the reach method, and reprogramming of sensitivity will significantly reduce the incidence of myopotential inhibition.     

Prospective Study of Cardiac Sarcoid Mimicking Arrhythmogenic Right Ventricular Dysplasia

Introduction: Case studies indicate that cardiac sarcoid may mimic the clinical presentation of arrhythmogenic right ventricular dysplasia/cardiomyopathy (ARVD/C); however, the incidence and clinical predictors to diagnose cardiac sarcoid in patients who meet International Task Force criteria for ARVD/C are unknown.
Methods and Results: Patients referred for evaluation of left bundle branch block (LBBB)-type ventricular arrhythmia and suspected ARVD/C were prospectively evaluated by a standardized protocol including right ventricle (RV) cineangiography-guided myocardial biopsy. Sixteen patients had definite ARVD/C and four had probable ARVD/C. Three patients were found to have noncaseating granulomas on biopsy consistent with sarcoid. Age, systemic symptoms, findings on chest X-ray or magnetic resonance imaging (MRI), type of ventricular arrhythmia, RV function, ECG abnormalities, and the presence or duration of late potentials did not discriminate between sarcoid and ARVD/C. Left ventricular dysfunction (ejection fraction <50%) was present in 3/3 patients with cardiac sarcoid, but only 2/17 remaining patients with definite or probable ARVD/C (P = 0.01).
Conclusions: In this prospective study of consecutive patients with suspected ARVD/C evaluated by a standard protocol including biopsy, the incidence of cardiac sarcoid was surprisingly high (15%). Clinical features, with the exception of left ventricular dysfunction and histological findings, did not discriminate between the two entities.     

Influence of Left Ventricular Lead Location on Outcomes in the COMPANION Study

Introduction: There are no randomized controlled trial data that evaluate mortality and hospitalization rates in cardiac resynchronization therapy (CRT) recipients based on left ventricular (LV) lead location. We analyzed the event-driven outcomes of mortality and hospitalization as well as functional outcomes including Functional Class, Quality-of-Life, and 6-minute walk distance in 1,520 patients enrolled in the COMPANION study of CRT versus optimal medical therapy.
Methods and Results: Over a mean follow-up after implantation of 16.2 months, patients randomized to CRT, regardless of lead location, experienced benefit compared with optimized pharmacologic therapy (OPT), with respect to all-cause mortality or heart failure hospitalization. All but a posterior location showed benefit with respect to the all-cause mortality or all-cause hospitalization outcome. Mortality benefit in CRT-D patients was indifferent to LV lead position. All functional outcomes including 6-minute walk distance, Quality-of-Life (QOL) and Functional Class improved with CRT, regardless of LV lead location.
Conclusion: LV lead location was not a major determinant of multiple measures of response to CRT therapy in the COMPANION Trial. While acute data indicate that a left lateral LV lead location results in the most favorable hemodynamic response, these chronic data suggest that positioning an LV lead in an anterior rather than a lateral or posterior LV location has similar benefit.     

Electrophysiologic Demonstration of an Atriofascicular Accessory Pathway

Evidence of an atriofascicular accessory pathway has not been reported previously. In the patient presented in this case report, an electrophysiology study demonstrated a constant left bundle branch block QRS configuration despite varying degrees of ventricular preexcitation, in association with a constant artrioventricular interval during incremental atrial pacing and programmed atrial stimulation. The presence of an atrioventricular, nodoventricular, nodofascicular, and atrial-His accessory pathway was ruled out. The findings are best explained by the presence of an underlying left bundle branch block and an atriofascicular accessory pathway connecting the atrium and right bundle. The atriofascicular accessory pathway was a passive bystander during an atrial tachycardia and was not directly involved in the generation of the tachycardia. To our knowledge, this is the first report of an atriofascicular accessory pathway.     

Temperature and Impedance Monitoring During Slow Pathway Ablation in Patients with AV Nodal Reentrant Tachycardia

Slow Pathway Ablation. Introduction : Successful radiofrequency ablation of an accessory pathway has been demonstrated to be associated with an electrode-tissue interface temperature of approximately 60°C or an impedance change of −5 to −10 Ω. However, the temperature and impedance changes associated with ablation of AV nodal reentrant tachycardia (AVNRT) using the slow pathway approach have not been reported. Therefore, the purpose of this study was to define the temperature and impedance changes achieved during ablation of AVNRT.
Methods and Results : The study included 35 consecutive patients with AVNRT undergoing radiofrequency ablation of the slow pathway with a fixed power output of 32 W, and using a catheter with a thermistor bead embedded in the distal 4-mm electrode. The procedure was successful in each patient. The steady-state electrode-tissue interface temperature during successful applications of energy was 48.5 ± 3.3°C (range 42° to 56°C), and the steady-state temperature during ineffective applications was 46.8°± 5.5°C (P = 0.03). The mean impedance change during all applications of energy was −1.4 ± 2.8 ω, and did not differ significantly during effective and ineffective applications. Coagulum formation resulted during five applications (2.7%) in two patients (5.7%). There were no recurrences during 114 ± 21 days of follow-up.
Conclusions : Successful ablation of AVNRT using fixed power output is achieved at an electrode-tissue interface temperature of approximately 48°C and is associated with a drop in impedance of 1 to 2 ω. These findings suggest that slow pathway ablation requires less heating at the electrode-tissue interface than does accessory pathway or AV junction ablation.     

Site of Accessory Pathway Block After Radiofrequency Catheter Ablation in Patients with the Wolff-Parkinson-White Syndrome

Site of Accessory Pathway Block. Introduction: Recent studies have demonstrated that the most common site of accessory pathway conduction block following the introduction of a premature atrial stimulus during atrial pacing is between the accessory pathway potential and the ventricular electrogram. consistent with block at the ventricular insertion of the accessory pathway. However, no prior study has evaluated the site of conduction block during radiofrequency catheter ablation procedures. Therefore, the objective of this study was to determine the site of conduction block after catheter ablation of accessory pathways by analyzing and comparing the local electrograms recorded before and after radiofrequency energy delivery at successful ablation sites. Methods and Results: The electrograms evaluated in this study were obtained from 85 consecutive patients who underwent successful radiofrequency catheter ablation of a manifest accessory pathway. The 50 left free-wall accessory pathways were ablated using a ventricular approach and the 35 right free-wall or posteroseptal accessory pathways were ablated using an atrial approach. The characteristics of local electrograms recorded immediately before and immediately after successful ablation of the accessory pathway were determined in each patient. The site of accessory pathway block was determined by comparing the amplitude, timing, and morphology of the local eleclrograms at successful sites of radiofrequency catheter ablation before and after delivery of radiofrequency energy. A putative accessory pathway potential was present at the successful target site in 74 of the 85 patients (87%). Conduction block occurred between the atrial electrogram and the accessory pathway potential in 66 patients (78%) and between the accessory pathway potential and the ventricular electrogram in eight patients (9%). The site of block could not be determined in 11 patients (13%) in whom an accessory pathway potential was absent. Conduction block occurred most frequently between the atrial electrogram and the accessory pathway potential regardless of accessory pathway location. No electrogram parameter or accessory pathway characteristic was predictive of the site of conduction block. Conclusion: The results of this study demonstrate that conduction block occurs most frequently between the local atrial electrogram and the accessory pathway potential during radiofrequency catheter ablation of accessory pathways. This is true regardless of whether the accessory pathway is ablated from the atrial or ventricular aspect of the mitral or tricuspid annulus.     

The Effect of Electrode Configuration on the Unipolar His-Bundle Electrogram

Although "unipolar electrograms" recorded from the His-bundle position have been used to help position catheters for His-bundle ablation, the techniques used to record such electrograms have not been standardized. The effects of five anode locations (right chest wall, anterior chest wall, left chest wall, posterior chest wall, and inferior vena cava) on unipolar atrial, His bundle and ventricular electrograms recorded from the His-bundle position were examined in ten patients undergoing clinical electrophysiology studies. Electrograms were recorded at filter settings of 50-500 as well as 0.05-1000 Hz. The location of the anode had no consistent effect on the amplitude, duration or morphology of any of the electrograms at either filter setting, but signals recorded with the inferior vena cava anode had the highest signal-to-noise ratio. A filter setting of 50-500 Hz decreased the amplitude of atrial (0.72 to 0.33 mV-P less than 0.01), His bundle (0.38 vs 0.32 mV-P less than 0.01) and ventricular electrograms (3.71 vs 2.01 mV-P less than 0.001) compared to a filter setting of 0.05-1,000 Hz. The filter setting did not affect electrogram duration. We concluded that the use of an electrode catheter in the inferior vena cava as the anode when recording "unipolar electrograms" from the His-bundle position yields a better signal-to-noise ratio than a skin patch on the chest and appears to be the optimal method for recording unipolar electrograms.