Biomedical subjects
Publications and source records attributed to John D Fisher.
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INTRODUCTION: Retroconduction (ventriculo-atrial conduction) remains a problem for patients with implanted cardiac rhythm devices. Pacemaker algorithms can detect and terminate endless loop tachycardia (ELT), but actual prevention of ELT may require anti-arrhythmic drugs (AADs). Similarly, AADs can affect ICD rhythm discrimination algorithms that depend on atrio-ventricular ratios. There is concern whether these drugs remain effective during stress situations. METHODS: Electrophysiologic studies that included retroconduction testing using slow ramp pacing were done in 1332 patients. The presence or absence of retroconduction at baseline and with drug was recorded, as was the rate at block. As a stress surrogate, isoproterenol was used to test retroconduction and reversal of drug-induced block. RESULTS: Procainamide, mexiletine, phenytoin, disopyramide, quinidine, beta-blockers, encainide, and amiodarone caused complete retrograde block or decreased the rate at which block occurred (mean 76% of patients, p < 0.008), whereas digoxin, lidocaine, diltiazem, and verapamil did not. Isoproterenol (in the absence of AADs) increased the rate at block in 82% of 404 patients with retroconduction at baseline (p < 0.005). Of 319 patients without retroconduction at baseline, 134 (42%) developed retroconduction after isoproterenol. Isoproterenol reversed retrograde block in 39% of patients with block on an AAD. Amiodarone, digoxin, and the combination of digoxin plus a beta-blocker were most effective at resisting this reversal of ventriculo-atrial block (80%, 68%, and 75% respectively). CONCLUSION: Most of the AADs reviewed increase the cycle length at block or abolish retroconduction, while isoproterenol has the opposite effect. Anti-arrhythmic medications, particularly amiodarone, digoxin, and the combination of digoxin plus a beta-blocker may be considered for a patient with multiple ELT episodes or certain ICD detection problems.
INTRODUCTION AND AIMS: Ablation of atrial fibrillation (AF) has evolved rapidly in the decade since its inception. We aimed to review the results of this evolution as reflected in the published literature. METHODS: Publications through 2005 were reviewed, and data included if there was information on the technique used, and follow-up of at least 6 months. RESULTS: More than 23,000 patients met criteria for inclusion. There has been a steady improvement in reported outcomes (P<0.001). Variations on radiofrequency catheter ablation for pulmonary vein isolation result in apparent elimination ("cure") or improvement of AF in 75%, and surgical techniques are even better. CONCLUSIONS: Catheter ablation of AF is now a mainstream procedure. Continuing technical advances are needed to achieve better results with more uniformity and reduced procedure times.
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A symptomatic woman with an electrocardiogram (ECG)-based diagnosis of Wolff-Parkinson-White (WPW) syndrome underwent electrophysiologic studies that revealed a likely fasciculo-ventricular tract.
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Left bundle branch block (LBBB) has negative hemodynamic effects. In the same patient, profound hypotension occurs during supraventricular tachycardia with LBBB but not at the same rate in the absence of LBBB. At slower rates, blood pressure is similar with and without LBBB.
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Opinions vary regarding the need to perform defibrillation testing prior to hospital discharge in recipients of state-of-the-art cardioverter defibrillators (ICDs). Our protocol is to perform predischarge ICD testing 1 day after implant. This report includes 682 consecutive implants. Adverse observations at testing were grouped into (1) risk of defibrillation failure, (2) surgical complications, (3) sensing/pacing issues or narrow defibrillation margin warranting closer follow-up, or (4) findings correctable by device reprogramming. Among the 682 patients, 63% had single-chamber and 37% dual-chamber or biventricular ICDs. In 48 patients (7%) there were 69 concerns and/or interventions, with overlaps among the four categories, including one failure to defibrillate (0.15%), and six other patients at risk. Surgical complications included 11 hematomas (1.6%), and six lead dysfunctions. Closer follow-up was indicated in 19 patients (2.7%), for high pacing thresholds in seven, sensing issues in seven, and <10 J defibrillation margin in five. Device reprogramming was needed in 31 patients (4.5%), for tachycardia detection and therapy settings in 12, and for pacing/sensing functions in 22 patients. In eight patients ventricular fibrillation could not be induced. There was no morbidity or mortality due to testing. The state-of-the-art ICDs delivering biphasic shocks are remarkably reliable. The routine pre-hospital discharge defibrillation testing of such ICDs may be optional and left to the physicians' discretion.
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Success rates of cardioversion with a defibrillator using the truncated exponential biphasic waveform (with a maximum energy of 360 J) and a defibrillator using the rectilinear biphasic waveform (with a maximum energy of 200 J) were randomly compared in 145 patients. Success rates at 50, 100, 150, and 200 J were not significantly different, but 2 patients who did not achieve cardioversion after a 200-J maximum energy shock by the rectilinear device underwent successful cardioversion with a 360-J shock by the truncated exponential device after crossover.
BACKGROUND: Stratifiers of sudden and total mortality risk are needed to optimally target preventive therapies in patients with coronary artery disease and impaired ventricular function. We assessed the prognostic significance of ECG markers of conduction abnormalities and left ventricular hypertrophy in the Multicenter Unsustained Tachycardia Trial (MUSTT). METHODS AND RESULTS: We analyzed the ECGs of 1638 patients from MUSTT who did not receive antiarrhythmic therapy (antiarrhythmic medication or implantable cardioverter-defibrillator). After adjustment for other significant factors, left bundle-branch block and intraventricular conduction delay were associated with a 50% increase in the risk of both arrhythmic and total mortality. Right bundle-branch block was not associated with arrhythmic or total mortality. Left ventricular hypertrophy was the only ECG predictor of arrhythmic (hazard ratio, 1.35; 95% CI, 1.08 to 1.69) but not total mortality. CONCLUSIONS: In patients with coronary artery disease, depressed left ventricular function, and nonsustained ventricular tachycardia, QRS prolongation resulting from left bundle-branch block or intraventricular conduction delay but not right bundle-branch block provided prognostic information about the risk of arrhythmic and total mortality independently of electrophysiological evaluation and ejection fraction. Left ventricular hypertrophy was associated with increased arrhythmic but not total mortality.
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Placement of a pacing lead into a branch of the coronary sinus for biventricular pacing sometimes is difficult or impossible. Surgical completion typically has included immediate or subsequent thoracotomy lead placement with hookup to the device at the time of chest surgery. We describe an alternative procedure of complete device-lead hookup and permanent pocket closure in the electrophysiology laboratory. The left ventricular lead is an epicardial type. The lead is tunneled to a position where the surgeon subsequently can recover it using the thoracotomy incision and implant the lead on the epicardium using device-based testing.
It is occasionally difficult to disconnect leads from headers at the time of pulse generator replacement without injuring the fragile leads. Over a 2.5-year period we encountered this problem in six cases (1.7% of pulse generator replacements). The posterior portion of the header was clipped off using an orthopedic bone cutter in four cases. The cut was aligned with the deep end of the lead socket in the header. A metal rod was then used to push the lead out of the socket. Bench testing of alternative methods was done on previously explanted pulse generators that were firmly held in a vice. Motorized microtools were used to drill holes from the end of the header to the deep end of the socket; or with a rotary saw attachment to slice off the back of the header, allowing a retained lead to be pushed out. The latter was also done with a hand held razor saw, and attempts were made with a scalpel. Lead removal in the clinical cases was accomplished quickly in the four cases using the bone-cutter, without trauma to the lead. Bench testing results varied. The bone cutter was the most efficient method for most brands, but was ineffective on one. The motorized tool was difficult to position, produced sprays of plastic particles, and would have been risky in a clinical setting. The razor saw was difficult to use safely, or efficiently, except in some headers that resisted the bone cutter. The scalpel failed except in one "soft header" pacemaker. An orthopedic bone cutter is a useful tool for removing a retained lead from a pulse generator header. Different header designs and materials necessitate knowledge of several lead detachment methods.
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