Sharon M. Dailey

Selective radiofrequency ablation of the slow pathway for the treatment of atrioventricular nodal reentrant tachycardia. Evidence for involvement of perinodal myocardium within the reentrant circuit.

BackgroundThe circuit of atrioventricular (AV) nodal reentrant tachycardia may include perinodal atrial myocardium. Furthermore, in patients with dual AV nodal pathways, the atrial insertion of the slow pathway is likely to be located near the ostium of the coronary sinus, caudal to the expected location of the AV node. The present study was designed to evaluate the safety and efficacy of selective catheter ablation of the slow pathway using radiofrequency energy applied along the tricuspid annulus near the coronary sinus ostium as definitive therapy for AV nodal reentrant tachycardia. Methods and ResultsAmong 34 consecutive patients who were prospectively enrolled in the study, the slow pathway was selectively ablated in 30, and the fast pathway was ablated in four. Antegrade conduction over the fast pathway remained intact in all 30 patients after successful selective slow pathway ablation. There was no statistically significant change in the atrio-His interval (68.5±21.8 msec before and 69.6±23.9 msec after ablation) or AV Wenckebach rate (167±27 beats per minute before and 178±50 beats per minute after ablation) after selective ablation of the slow pathway. However, the antegrade effective refractory period of the fast pathway decreased from 348±94 msec before ablation to 309±79 msec after selective slow pathway ablation (p = 0.005). Retrograde conduction remained intact in 26 of 30 patients after selective ablation of the slow pathway. The retrograde refractory period of the ventriculoatrial conduction system was 285±55 msec before and 280±52 msec after slow pathway ablation in patients with intact retrograde conduction (p = NS). There were three complications in two patients, including an episode of pulmonary edema and the development of spontaneous AV Wenckebach block during sleep in one patient after slow pathway ablation and the late development of complete AV block in another patient after fast pathway ablation. Over a mean follow-up period of 322±73 days, AV nodal reentrant tachycardia recurred in three patients, all of whom were successfully treated in a second ablation session. ConclusionsRadiofrequency ablation of the slow AV pathway is highly effective and is associated with low rate of complications.

Radiofrequency ablation for treatment of primary atrial tachycardias

OBJECTIVES The purpose of this study was to determine the safety and efficacy of radiofrequency ablation as definitive therapy for primary atrial tachycardias. BACKGROUND Primary atrial tachycardias are often difficult to control with antiarrhythmic medications and frequently require nonpharmacologic interventions for definitive therapy. Despite isolated reports of successful treatment of primary atrial tachycardias with radiofrequency ablation, the safety and efficacy of this technique have not been established in a larger series with long-term follow-up. METHODS The immediate procedural success rate, associated complications and follow-up data of radiofrequency ablation were evaluated in 15 consecutive patients (11 adults and 4 children) with primary atrial arrhythmias that were refractory to medical management. RESULTS The clinical arrhythmia was ectopic atrial tachycardia in 11 patients and sinus node reentry in 4. The site of origin of the tachycardia was in the right atrium in 14 patients and in the left atrium in 1 patient (with two distinct foci) where the local atrial electrogram preceded the onset of the P wave by 10 to 30 ms. Radiofrequency energy successfully terminated the primary atrial tachycardia in each of the patients, and all were discharged from the electrophysiology laboratory in sinus rhythm without inducible atrial tachycardia. A mean of 10.8 +/- 9.9 radiofrequency applications were delivered using 30 W of power for 30 s. The local intracardiac activation time (relative to the P wave in the surface electrocardiogram) was a mean of -21 +/- 5 ms at the successful ablation site and -15 +/- 6 ms at unsuccessful sites (p < 0.001). No complications were observed, although one patient with incessant ectopic atrial tachycardia had sinus pauses after ablation. During a mean follow-up period of 277 +/- 133 days, the clinical arrhythmia recurred in three patients (20%, 95% confidence intervals 3% to 37%) including two patients with ectopic atrial tachycardia and one patient with sinus node reentry. One of these patients was successfully treated in a second ablation session. CONCLUSIONS Thus, radiofrequency catheter ablation appears to be a safe and effective technique for the treatment of primary atrial arrhythmias that are refractory to antiarrhythmic medications.

Role of Radiofrequency Ablation in the Management of Supraventricular Arrhythmias:.: Experience in 760 Consecutive Patients

Radiofrequency Ablation of Supraventricular Arrhythmias, Introduction: Several reports iiave demonstrated that radiofrequency catheter ablation provides effective control of a variety of supraventricular tachycardias. However, the efficacy, complications, risk of arrhythmia recurrence, and follou‐up survival analysis have not been reported in a large series of consecutive patients with supraventricular arrhythmias with diverse electrophysiologic mechanisms. This report details the results of radiofrequency catheter ahiation in 760 consecutive patients (386 males, 374 females) with a wide variety of supraventricular tachycardias treated at one center.

Clinical characteristics and outcome of patients with high defibrillation thresholds. A multicenter study.

BackgroundSuccessful defibrillation by an implantable cardioverter-defibrillator (ICD) depends on its ability to deliver shocks that exceed the defibrillation threshold. This study was designed to identify clinical characteristics that may predict the finding of an elevated defibrillation threshold and to describe the outcome of patients with high defibrillation thresholds Methods and ResultsThe records of 1,946 patients from 12 centers were screened to identify 90 patients (4.6%) with a defibrillation threshold ≥25 J. Excluding three patients who received ICDs that delivered >30 J, there were 81 men and six women with a mean age of 59.5plusmn;10.1 years, a mean left ventricular ejection fraction of 0.32plusmn;0.14, and a 76% prevalence of coronary artery disease. Sixty-one patients (70%) were receiving antiarrhythmic drugs, and 45 (52%) were receiving amiodarone. Seventy-one patients (82%) received an ICD. Death occurred in 27 patients −19 of the 71 (27%) with an ICD (eight arrhythmic), and eight of the 16 (50%) without an ICD (four arrhythmic). Actuarial survival for all patients at 5 years was 67%. Actuarial survival rates at 2 years for patients with and without an ICD were 81% and 36%, respectively (p = 0.0024). Actuarial survival at 5 years for the ICD patients was 73%; no patient without an ICD has lived longer than 32 months. Actuarial survival free of arrhythmic death in the ICD patients at 5 years was 84%. Although the only variable to predict survival was ICD implantation (p = 0.003), it is entirely possible that in this retrospective analysis, clinical selection decisions to implant or to not implant an ICD differentiated patients destined to have better or worse outcomes, respectively. ConclusionsAntiarrhythmic drug use may be causally related to the finding of an elevated defibrillation threshold. When patients with high defibrillation thresholds receive an ICD, arrhythmic death remains an important risk (42% of deaths in these patients were arrhythmia related, with 16% actuarial incidence at 5 years). Vigorous testing to optimize patch location can potentially benefit patients by enhancing the margin of safety for effective defibrillation.

Intracoronary ethanol ablation for the treatment of recurrent sustained ventricular tachycardia

The selective infusion of ethanol into the coronary circulation supplying the site of origin of incessant ventricular tachycardia has been demonstrated to abolish this arrhythmia in selected patients. The present study was designed to evaluate the efficacy and safety of the intracoronary ethanol ablation technique in patients with paroxysmal ventricular tachycardia related to prior myocardial infarction. Twenty-three patients with sustained monomorphic ventricular tachycardia that was refractory to conventional antiarrhythmic drug therapy were prospectively studied. After induction of ventricular tachycardia by programmed electrical stimulation, the response of the arrhythmia to the infusion of radiographic contrast medium or saline solution into the ostia of the native coronary arteries and coronary artery bypass grafts was assessed. If ventricular tachycardia was reliably interrupted by injections into the proximal coronary artery or bypass graft, the vessel was cannulated with a steerable guide wire and 2.7F infusion catheter to determine the smallest arterial branch that would result in termination of the arrhythmia with selective injections. If reliable interruption of ventricular tachycardia was observed with saline or contrast injections, ethanol (2 ml) was then delivered through the infusion catheter. Ventricular tachycardia could be terminated by injections of saline solution or contrast medium in 11 of 21 patients in whom the protocol could be completed. Ethanol was infused in 10 of these patients. Ventricular tachycardia was inducible in only 1 of 10 patients immediately after ethanol infusion. At a follow-up electrophysiologic study performed 5 to 7 days after ablation, ventricular tachycardia became inducible in two other patients, in one of whom the arrhythmia substrate was successfully ablated after three sessions. The mean left ventricular ejection fraction was 0.33 +/- 0.1 before and 0.35 +/- 0.11 after ablation. Complications of the procedure included complete atrioventricular block in four patients and pericarditis in one patient. Thus, intracoronary ethanol ablation is associated with a moderate degree of efficacy but the potential for important complications. Despite these limitations, this technique may provide effective long-term control of ventricular tachycardia for some patients.

A prospective evaluation of intracoronary ethanol ablation of the atrioventricular conduction system.

The clinical efficacy and complications associated with ablation of the atrioventricular (AV) conduction system by the selective infusion of ethanol into the AV node artery were prospectively assessed in 12 consecutive patients with medically refractory atrial arrhythmias. Six of the patients had previously failed to have permanent complete AV block created with direct current or radiofrequency catheter ablation. The AV node artery was cannulated with a 0.016 in. (0.041 cm) guide wire in all 12 patients. It was also possible to advance a 2.7F infusion catheter into the AV node artery in all patients. Transient AV block was induced by selective injections into the AV node artery of iced saline solution (8 patients) and of radiographic contrast agent (ioxaglate) (10 patients). The infusion of 2 ml of ethanol (96%) induced immediate complete AV block in all 10 patients who demonstrated AV block with ioxaglate. The escape rhythm exhibited a narrow QRS complex preceded by a His bundle deflection in nine patients and left bundle branch block in one patient. The immediate mean rate of the escape rhythm was 45.3 +/- 13.4 beats/min. In two patients who demonstrated reflux of contrast agent into the distal right coronary artery with selective injections into the AV node artery, transient ST segment elevation developed in the inferior electrocardiographic leads with the infusion of ethanol. There was no change in the left ventricular ejection fraction from the baseline value (0.53 +/- 0.12) to that measured after ablation (0.55 +/- 0.11) and no patient developed wall motion abnormalities.(ABSTRACT TRUNCATED AT 250 WORDS)

Relationship Between Heart Rate and Oxygen Kinetics During Constant Workload Exercise

Background: Oxygen uptake during constant workload exercise increases exponentially from its resting value before reaching a steady state. The difference between the actual rate of oxygen consumption at the onset of exercise and the steady state is an oxygen deficit. Similarly, the normal sinus node increases its rate at the onset of exercise before achieving a steady state, thereby producing a heart rate deficit. The purpose of this study was to test the hypothesis that elimination of the heart rate deficit by an instantaneous increase in heart rate at the onset of constant workload exercise to the steady‐state level would reduce the oxygen deficit and improve the perceived difficulty of exertion as compared with the chronotropic response of the normal sinus node. Methods and Results: Ten subjects with normal sinus node function who had DDD pacemakers implanted for A V block completed a symptom‐limited maximal treadmill exercise test using the Chronotropic Assessment Exercise Protocol (CAEP) to assess sinus node function, maximal heart rate, and VO2 max. The subjects then performed constant workload exercise tests (6‐min duration) at a workload equal to approximately 50% of metabolic reserve with the pacemaker randomly programmed to each of three patterns of chronotropic response: (1) DDD (lower rate 60 beats/ min); (2) Fast (lower rate abruptly programmed to the expected value at 50% metabolic reserve); and (3) Overpaced (lower rate at least 80% of the age predicted maximum). The oxygen deficit was lower with the fast chronotropic response (434 ± 238 ml O2) than with either the DDD (512 ± 233; P = 0.02), or overpaced chronotropic patterns (488 ± 238; P = 0.02 vs fast). The rate constant for change in VO2 was highest with the fast chronotropic pattern (2.85 ± 1.38) compared with either the DDD (2.25 ± 0.64; P = 0.01) or overpaced (2.38 ± 0.43; P = 0.02) patterns. The Borg perceived exertion rating was lowest with the fast chronotropic response (P = 0.02 vs DDD and P = 0.02 vs overpaced). Conclusions: The results of this study suggest that oxygen kinetics and exertional symptoms are improved by an abrupt increase in pacing rate at the onset of exercise to a value that is appropriate for metabolic demand as compared with the DDD pacing mode in patients with normal sinus node function. In contrast, an overly aggressive chronotropic response was not associated with improved oxygen kinetics or exertional symptoms.

Gross and Microscopic Changes Associated with a Nonthoracotomy Implantable Cardioverter Defibrillator

The pathology associated with an invesrigational transvenous defibriliating and sensing lead is described. The lead system had delivered a total of 865 J from the time of implantation to the time of patient death from a noncardiac cause 7 months after implantation and 1 month after his last defibrillator shock. There was mild, superficial fibrous thickening on the endothelial surface of the superior vena cava adjacent to the proximal spring electrode, which did not extend into the vessel wall. The distal portion of endocardial lead was embedded in the interventricular septum near the apex of the right ventricle, surrounded by fibrous thickening, and partially covered by endocardial tissue. Microscopically, there was a thick bed of fibrous connective tissue surrounding the lead with extensive interstitial fibrous connective tissue radiating into the adjacent myocardium. Since this pattern is different from the more generalized fibrotic scarring produced by myocardial infarction, we speculate that the mechanism for the observed interstitial fibrosis is replacement fibrosis following acute myocyte injury that resulted from prior defibrillator shocks and possibly from the trauma produced by the lead compressing adjacent myocardium during systole. Potential effects on device efficacy of these fibrotic changes at the bioelectric interface include their representing a new arrhythmia substrate, the possibility that fibrosis could increase both defibrillation and pacing thresholds, and that the inflammatory reaction may cause deterioration of intracardiac electrograms and interfere with sensing and tachycardia recognition.

Effect of Chronotropic Response Pattern on Oxygen Kinetics

Background: The sinus node is considered to be the model of chronotropic response for pacemakers that use artificial rate modulating sensors. Maximal metabolic exercise testing with measurement of oxygen consumption (VO2) is frequently used to evaluate chronotropic response. Since activities of daily living are generally transient and involve submaximal effort, maximal exercise testing may not provide the most clinically relevant method of assessing rate modulation. The purpose of this study was to determine if an abrupt increase in heart rate (HR) at the onset of submaximal exercise provides improved oxygen kinetics compared with a linear response. Methods and Results: Thirteen patients with complete heart block and permanent rate modulating pacemakers implanted following catheter ablation of the atrioventricular junction for refractory atrial fibrillation were chosen for study. The patients first completed a maximal treadmill exercise test using the chronotropic assessment exercise protocol with breath‐by‐breath analysis of expired gases. The expected HR at 50% of metabolic reserve was calculated for each patient. Three submaximal constant workload exercise tests were then performed at 50% of each patients metabolic reserve, with the pacemaker randomly programmed to provide three different patterns of chronotropic response: linear (in which HR increased from 70 beats/min to the expected HR at 50% of metabolic reserve), fast(in which HR was abruptly increased to the expected HR at 50% of metabolic reserve), and slow (VVI at 70 beats/ min). Oxygen kinetics were compared for the three patterns of chronotropic response. Cumulative oxygen (O2) consumption was significantly greater for the fast pattern (3610 mL) as compared with the linear (3487 mL, P = 0.004) or slow pattern (3277 mL). The O2 deficit was lower for the fast (361 ± 139 mL) than for the linear (539 ± 225 ml, P = 0.003) or slow chronotropic pattern (559 ± 194). Similar improvements in the rate constant of O2 uptake and Borg perceived exertion scores were observed with the fast chronotropic response pattern. Conclusion: A rapid increase in pacing rate at the onset of exercise improves oxygen kinetics and results in less perceived exertion as compared to a more gradual rate increase that is more characteristic of sinus node behavior.

Inability of the signal-averaged electrocardiogram to determine risk of arrhythmia recurrence in patients with implantable cardioverter defibrillators.

Signal‐averaged electrocardiography has been used to identify patients at risk for arrhythmic death after myocardiaJ infarction. Since patients with implantable Cardioverter defibrillators (ICDs) are at high risk for arrhythmic events, they should also be expected to have a high incidence of abnormal signal‐averaged electrocardiograms (SAECGs). However, whether the SAECG can discriminate patients who will have arrhythmia recurrence and receive appropriate ICD shocks from those who will have no recurrence and no shocks is unknown. This study examines the usefulness of the SAECG to separate appropriate users from non‐users of the ICD. Fifty patients with ICDs participated in this study. Those who received a shock preceded by symptoms, a shock without preceding symptoms but with electrocardiographic documentation of ventricular fibrillation or ventricular tachycardia, or a shock while asleep were classified as ICD users. All other patients were classified as nonusers. The SAECG was classified as normal if the QRS duration on the standard electrocardiogram was ≤ 110 msec and if the total filtered QRS duration was < 120 msec, the root‐mean square voltage of the terminal 40 msec was > 25 μV, and the terminal low amplitude signal duration measured < 38 msec. The SAECG was classified as abnormal if the QRS duration on the standard electrocardiogram was ≤ 110 msec and any one of these three criteria were outside the “normal range.” The SAECG was classified as indeterminate if the QRS duration on the standard 12‐lead electrocardiogram was > 110 msec. For the entire group of 50 patients, 8 (16%), 12 (24%), and 30 (60%) had normal, abnormal, and indeterminate SAECGs, respectively. Of the 22 ICD users, 1 (5%), 5 (23%), and 16 (73%) patients had normal, abnormal, and indeterminate SAECGs, respectively. Of the 28 ICD nonusers, 7 (25%), 7 (25%), and 14 (50%) patients had normal, abnormal, and indeterminate SAECGs, respectively. ICD users had lower left ventricular ejection fractions (P = 0.0002J, a higher incidence of ventricular tachycardia (P = 0.04J, prior exposure to a greater number of antiarrhythmic drugs (P = 0.04), and a lower likelihood for survival (P = 0.02) compared to the ICD nonusers. There was no statistically significant difference between the ICD users and nonusers as stratified by SAECG classification regardless of whether or not the indeterminate studies were included or excluded from the analysis. When the analysis was restricted to the 35 patients with coronary artery disease and mono‐morphic ventricular tachycardia, again there was no statistically significant difference between the ICD users and nonusers as stratified by the SAECG classification. In a Cox analysis no SAECG parameter entered the model to predict ICD use. Thus, appropriate ICD discharges occurred regardless of the outcome of signal‐averaged electrocardiography. The data suggest that the SAECG should not be used in the decision analysis whether to implant or deny ICD implantation for patients who have demonstrated life‐threatening ventricular arrhythmias.