Atrioventricular Node Modification Research Articles

Management of Atrial Fibrillation in Adults: Prevention of Thromboembolism and Symptomatic Treatment

Because of its prevalence in the population and its associated underlying diseases and morbidity, atrial fibrillation (AF) is an important and costly health problem. Advancing age, diabetes, heart failure, valvular disease, hypertension, and myocardial infarction predict the occurrence of AF within a population. The management of AF is complex and involves prevention of thromboembolic complications and treatment of arrhythmia-related symptoms. Stroke occurs in 4.5% of untreated patients with AF per year. Independent risk factors for stroke in nonrheumatic patients with AF are advanced age; a history of prior embolism, hypertension, or diabetes; and echocardiographic findings of left atrial enlargement and left ventricular dysfunction. Warfarin decreases stroke by two-thirds and death by one-third; aspirin is only about half as effective overall and is insufficient therapy for those with risk factors for stroke. Options for thromboembolic prophylaxis are use of warfarin for all in whom it is safe or, alternatively, warfarin for those with risk factors and aspirin for those without risk factors. One-half of the patients with AF are 75 years of age or older. The uniform applicability and relative safety of warfarin therapy in this age-group are controversial. Specific therapy for the arrhythmia should be dictated by the need to control symptoms. Symptomatic treatments include rate-control medications and strategies designed to terminate and prevent arrhythmia recurrence. Digoxin, beta-adrenergic blockers, verapamil, and diltiazem slow excessive ventricular rates in patients with AF and may favorably manage comorbid conditions. The efficacy of anti-arrhythmic medications is only 40 to 70% per year in preventing recurrences of AF, and these agents, except amiodarone, may increase the risk of sudden death in patients with certain types of organic heart disease and AF. The use of nonpharmacologic symptomatic therapies such as atrioventricular node modification or ablation with a rate-response pacemaker or surgical intervention is increasing.

Transcatheter modification of the atrioventricular node in dogs, using radiofrequency energy

Abstract Objective To develop a protocol for reliably inducing atrioventricular (AV) block (ideally first- or second-degree), using radiofrequency energy. Design An electrosurgical unit was coupled to an ammeter, which was connected to the distal pole of an electrode catheter positioned at the AV node. Control settings had previously been calibrated to the power output in a circuit with a 100-ohm resistance. Animals 10 clinically normal dogs. Procedure Transcatheter AV nodal modification was attempted, using progressive power applications of 10 to 20 W for progressive durations of 10 to 30 seconds. Atrioventricular nodal conduction and refractivity were measured before and 20 minutes and 1 month after ablation. Electrocardiograms were monitored throughout the 1-month period. Results Eight of the 10 dogs developed complete AV block, 1 developed stable 2:1 AV block, and another had no long-term change in AV nodal conduction. Four dogs attained their maximal degree of AV block in 2 to 5 days. Three of these had no AV nodal conduction changes until 2 to 4 days after ablation. Conclusions An electrosurgical unit can be economically modified for radiofrequency transcatheter ablation. Stable, incomplete AV block was rarely induced using this protocol, whereas complete AV block often developed. A major finding was frequent delay between energy delivery to the AV nodal region and induction of AV block. Clinical Relevance Induction of complete AV block using this technique, followed by permanent pacemaker placement, is an effective alternative to long-term antiarrhythmic treatment in animals with chronic atrial arrhythmias. Transcatheter ablation could be used to treat other forms of tachycardia, as it is in human medicine.

Prevention works; so does treatment (if you make it to the doctor)

In 1995, clinical trials in cardiology brought good news to both the interventionalist hawks and the diet-conscious, psychosocially minded doves. Hypertension highlights included case-control studies suggesting that nifedipine increases mortality of hypertensive patients with coronary artery disease, and that diuretics sparing magnesium and potassium (triamterene, spironolactone, amiloride) have a third to a half the risk of sudden cardiac death of thiazide or loop diuretics. Atherosclerosis research was dominated by the revelation that statins ~educe progression of atherosclerosis, infarction, and mortality from all causes in men (non-significant trend in women) up to 70 years of age with known coronary disease. Benefit was apparent even in those with average cholesterol, which by definition can no longer be called normal. In the West of Scotland trial of men aged 45-64 with moderate hypercholesterolaemia, normal blood pressures, and no previous infarction, pravastatin reduced total mortality by 22% at 5 years. Nine randomised trials have now compared bypass with angioplasty. Mortality overall is identical; bypass is probably preferable for patients with left main or multiple severe stenoses, particularly with ventricular dysfunction or diabetes. Those with two or three vessel disease with little ventricular dysfunction may opt for angioplasty because of the reduced morbidity (including stroke) and earlier return to work; costs are slightly lower. These trials preceded the introduction of stents, which should further reduce costs and need for reintervention. Restenosis is now less of a problem in the larger coronary segments amenable to stenting. Ticlopidine has reduced the need for warfarin, and heparin coating of stents reduces reocclusion. Other new approaches to overcome restenosis include local delivery of radiation and toxins, the antisense oligonucleotide to c-myc, and growth factors to accelerate endothelial regeneration. Myocardial infarction trials showed improved survival with angiotensin-converting enzyme inhibitors given in the first 24 hours. Routine angioplasty and intra-aortic balloon pumping seem to save lives. Heart failure trials were notable for the 67% reduction in mortality with carvedilol, a p-blocker with some o!-blocking and antioxidant properties. Low starting doses are advised. Atrial fibrillation now seems amenable to atrioventricular node modification to reduce the ventricular response. Atrial flutter responds to ablation of the reentrant circuit; ventricular tachycardia less so. Preliminary results from trials of the automatic implanted cardioverter defibrillator suggests that lives will be saved although benefits relative to amiodarone and [3-blockers will not be

Effect of dual atrioventricular node pathways on atrioventricular reentrant tachycardia.

Dual atrioventricular (AV) node pathway physiology is frequently observed in patients with AV accessory pathways. To examine the implications of this, we identified 36 patients (19 men and 17 women; mean +/- SD age, 30 +/- 13 years) with both phenomena. The 36 patients had 48 accessory pathways. Twenty-seven patients had bidirectional and 9 had unidirectional accessory pathways. Of the 34 patients with inducible atrioventricular reentry, 17 used the slow and 11 used the fast anterograde AV node pathway exclusively during AV reentrant tachycardia, whereas 6 patients used both the fast and the slow AV node pathways. AV node reentrant tachycardia was inducible in addition to AV reentry in 7 patients. Both the cycle length and AH intervals were significantly longer during slow pathway-dependent (cycle length, 411 +/- 58 milliseconds [ms]; AH, 229 +/- 42 ms) than during fast pathway-dependent (cycle length, 322 +/- 40 ms; AH, 121 +/- 25 ms; P < .05) reentrant tachycardias. Two patients had only AV node reentrant tachycardia inducible despite the presence of the accessory pathway. Four patients with technically difficult accessory pathways were managed by AV node modification with slow pathway (3) or fast pathway (1) ablation. Three of them remained free of symptoms 7, 14, and 25 months after the procedure whereas 1 patient had recurrence of arrhythmia. AV reentrance with dual AV node pathways frequently depends exclusively on either the slow or the fast AV node pathway for clinical tachycardia. This may provide additional options for ablation in technically difficult cases when the accessory pathway is not otherwise problematic.

Ablative therapy for atrioventricular nodal reentry arrhythmias

Recent studies in the clinical electrophysiology laboratory have advanced our understanding of the physiologic anatomy of the atrioventricular (AV) junction and have helped direct new curative techniques for the treatment of AV nodal (junctional) reentry. In most patients, it appears that the AV node or the inputs to the AV node that constitute the “slow” pathway are located caudal to the compact AV node and His bundle region near the os of the coronary sinus. In contrast, conduction over the “fast” pathway appears to be located along the anterior tricuspid annulus proximal to the traditional His bundle recording position. This physiologic heterogeneity has allowed the development of curative techniques for AV nodal reentry. The current preferred technique involves ablation of the slow pathway by delivering radiofrequency lesions in the region of the coronary sinus ostium. Although several different localization techniques have been developed, the overall success rate for the procedure includes a primary success rate that should be over 95%, a 5% to 10% late recurrence rate, and a complication rate of under 2%. Complete heart block as a complication of slow AV nodal pathway ablation is rare but can occur. The improvements in the results of radiofrequency ablation for the treatment of AV nodal reentry have resulted in the increased use of this procedure clinically. It is now reasonable to offer young patients AV nodal modification as primary therapy for AV nodal reentry and to apply the technique in all age groups to drug-resistant patients.

Control of rapid ventricular response by radiofrequency catheter modification of the atrioventricular node in patients with medically refractory atrial fibrillation.

Pharmacological control of rapid ventricular response to atrial fibrillation may be difficult in some patients. Alternative treatments, including curative surgery or atrioventricular (AV) node ablation with pacemaker implantation, have significant potential morbidity. In view of evidence that dual AV nodal physiology may exist in a significant percentage of the population, even in those without AV nodal reentrant tachycardia, we postulated that control of ventricular response might be achieved by radiofrequency (RF) catheter ablation in the region of the AV nodal slow pathway with its short refractory period. Ten patients underwent attempted AV node modification using a 4-mm-tipped electrode catheter positioned in the middle or posterior septum, between the His bundle and coronary sinus ostium on the tricuspid valve annulus. RF energy was applied at 16 to 30 W for up to 60 seconds, until average ventricular response fell below 100 beats per minute. Reduction of maximal ventricular response below 120 beats per minute was confirmed with atropine 1 mg IV. If required, additional ablations were performed progressively more posteriorly up to the coronary sinus ostium. Patients with successful AV node modification were discharged off AV node-blocking drugs and followed in the clinic at regular intervals. Twenty-four-hour ambulatory ECG recordings and/or treadmill stress tests were obtained before and after ablation for statistical comparison of maximum ventricular rate. Resting average ventricular rate was determined during electrophysiology study before and after ablation. In 7 of 10 patients (70%), maximum ventricular rate was reduced from a mean of 164 +/- 12 to 123 +/- 16 beats per minute (P < .01) and average ventricular rate from a mean of 128 +/- 11 to 83 +/- 10 beats per minute after ablation. Mean minimum ventricular rate was 54 +/- 11 beats per minute after ablation. These 7 patients have remained symptom free from rapid ventricular response for a mean of 14 +/- 8 months (range, 1 to 22). Three remain off all AV node-blocking drugs, 3 remain on digoxin alone, which was previously ineffective, and 1 remains on a beta-blocker for angina. In the 3 patients who did not respond to AV node modification, complete AV node ablation and permanent pacemaker implantation was performed in 2 and DC cardioversion after amiodarone loading was performed in 1. RF catheter modification of AV node conduction is effective in controlling rapid ventricular response to atrial fibrillation in a significant percentage of medically refractory patients. A possible mechanism of RF modification of AV node conduction is AV nodal slow pathway ablation. Large-scale clinical trials will be needed to determine the overall efficacy and safety of this technique.

Efficacy and safety of atrioventricular nodal modification for atrioventricular nodal reentrant tachycardia in the pediatric population

The safety and efficacy of radiofrequency catheter modification of the atrioventricular node for atrioventricular nodal reentrant tachycardia in the pediatric population is described. Twenty-one patients with a mean age of 14.9 ± 3.6 years underwent slow-pathway atrioventricular nodal modification with a stepwise anatomic approach. The average cumulative fluoroscopy exposure time (22 procedures in 21 patients) inclusive of the electrophysiologic study was 36.1 ± 22 minutes. Noninducibility of tachycardia was achieved in all patients with one procedural complication (hemothorax). During a mean follow-up of 15 ± 9.06 months, tachycardia recurred in one patient. Patient and family acceptance and satisfaction with the procedure was high. Because of the curative potential of radiofrequency catheter modification with low associated short- and long-term risks, it may be considered as a primary treatment option in pediatric patients with symptomatic atrioventricular nodal reentrant tachycardia.

Curative Transcatheter Radiofrequency Current Ablation for Atrioventricular Nodal Reentry Tachycardia

To evaluate the efficacy of atrioventricular nodal modification by transcatheter ablation using radiofrequency energy in preventing electrically inducible and spontaneous symptomatic atrioventricular nodal reentry tachycardia, a prospective, nonrandomized, "before-after" trial was performed. Fifty consecutive patients with recurrent spontaneous symptomatic atrioventricular nodal reentry tachycardia referred to the Massachusetts General Hospital, Boston, were recruited. A diagnostic intracardiac electrophysiologic study was performed to define the mechanism of each patient's supraventricular tachycardia. Thereafter, selective ablation of one or more slow atrioventricular nodal pathways was attempted in 47 patients, and in three patients selective ablation of a retrograde fast atrioventricular nodal pathway was carried out. Repeated programmed cardiac stimulation was performed 30 minutes after catheter ablation therapy and, where possible, before hospital discharge to evaluate the presence of electrically inducible supraventricular tachycardia. Electrically inducible atrioventricular nodal reentry tachycardia was eliminated in all 50 patients. No patient developed early heart block. During a mean (+/- SD) follow-up period of 8.9 +/- 5.3 months, three patients experienced a recurrence of spontaneous atrioventricular nodal reentry tachycardia and underwent a successful second ablation procedure. Two patients required permanent pacemaker implantation, one for symptomatic first-degree atrioventricular block and one for late complete heart block. Catheter ablation of slow atrioventricular nodal pathways by means of radiofrequency current is a safe and effective technique for eliminating electrically inducible and spontaneous atrioventricular nodal reentry tachycardia.

Radiofrequency catheter ablation in the treatment of supraventricular tachycardia in the elderly

Objectives. The purpose of this study was to evaluate the efficacy and safety of radiofrequency catheter ablation for the treatment of supraventricular tachycardias in an elderly (≥70 years of age) group of patients.Background. Supraventricular tachycardias are the most common form of cardiac arrhythmia and affect all age groups. Although usually well tolerated in youth, supraventricular tachycardias may be associated with disabling symptoms and have lifethreatening potential 10 the elderly. In addition, antiarrhythmic agents are less well tolerated and may be associated with a higher incidence of toxicity in the elderly.Methods. From May 1989 to March 1993, 454 patients underwent a radiofrequency catheter ablation procedure at the University of California, San Francisco, for the treatment of symptomatic supraventricular tachycardia. Sixty-seven of these patients were ≥70 years of age and constituted the study group. Patients underwent one of the following catheter ablation procedures: complete atrioventricular (AV) junctional ablation for ventricular rate control in patients with atrial fibrillation (37 patients), AV node modification for the treatment of AV node reentrant tachycardia (17 patients), accessory pathway ablation (9 patients), ablation of the “slow zone” to cure atrial flutter (4 patients) and atrial tachycardia ablation (1 patient). One patient underwent ablation for both AV node reentrant tachycardia and atrial flutter.Results. Success was achieved in 67 (98.5%) of 68 ablation procedures. There were no procedural or early deaths. The overall complication rate was 7.4%, and only one patient (1.5%) had long-term sequelze (permanent cardiac pacing for complete heart block). At a mean (±SD) follow-np of 22.1 ± 12.9 months, 63 (94%) of 67 patients were alive, with no antiarrhythmic agents for the treatment of their presenting arrhythmia.Conclusions. In this series radiofreqnency catheter ablation appears to be an effective and safe treatment option for elderly patients (≥70 yean of age) with a variety of symptomatic, drug-resistant supraventricular tachycardias. Because of the high incidence of severe symptoms associated with tachycardic episodes, the expense and the possible severe proarrhythmic problems associated with antiarrhythmic medications in this age group, catheter ablation may be considered an early rather than a “last resort” treatment option.

Elimination of slow pathway conduction: An accurate indicator of clinical success after radiofrequency atrioventricular node modification

Objectives. The purpose of this study was to determine the optimal end point of radiofrequency atrioventricular (AV) node modification using anatomically guided slow pafhway approaches in patients with AV node reentrant tachycardia.Background. The optimal end point for AV node modification using radiofrequency energy is uncertain, although elimination of inducible AV node reentrant tachycardia has been used.Methods. We followed up 51 consecutive patients (40 women, 11 men, mean age ± SD 41 ± 16 years) with symptomatic AV node reentrant tachycardia for 12 ± 6 months (range 4 to 24) after radiofrequency AV node modification using an anatomically guided slow pathway approach. Inducible AV node reentrant tachycardia was eliminated in all patients, whereas residual slow pathway conduction persisted in 12 patients (24%) after ablation. One study was complicated by complete AV block and two patients were lost to follow-up (one with and one without residual slow pathway conduction).Results. Clinical recurrence of AV node reentrant tachycardia was documented in seven patients (14%) 3 days to 3 months (median 1 month) after ablation. The recurrence rate was significantly higher in patients with than in those without residual slow pathway conduction (6 [55%] of 11 vs. 1 [3%] of 37, p < 0.01). The recurrence rate was not different between patients with only residual slow pathway conduction and those with residual slow pathway conduction and inducible single echo cycles (three [60%] of five in both groups, p = NS). The number of radiofrequency energy applications was not significantly different between those without and those with recurrence (20 ± 17 vs. 16 ± 9, p = NS). Junctional tachycardia during application of radiofrequency energy tended to be more frequently observed in those with a successful outcome (77% vs. 57%, p > 0.05). Of the 22 who underwent modification before 1992, residual slow pathway conduction was present in 9 (41%) of 22 patients. Atrioventricular node reentrant tachycardia recurred in five (56%) of these nine patients. A greater effort made in 1992 to eliminate slow pathway conduction in 29 patients resulted in residual slow pathway conduction in only 3 (11 %) with recurrence in 2 (4%).Conclusions. Complete elimination of slow pathway conduction is feasible in the majority of patients. Elimination of slow pathway conduction is highly predictive of long-term success after AV node modification using an anatomically guided approach.

Alterations of heart rate and of heart rate variability after radiofrequency catheter ablation of supraventricular tachycardia. Delineation of parasympathetic pathways in the human heart.

Persistent inappropriate sinus tachycardia has been reported as a complication after radiofrequency (RF) ablation of the fast atrioventricular (AV) nodal pathway. The purpose of this study was to evaluate the prevalence of this complication and its mechanism using heart rate variability analysis. Time and frequency domain analysis of heart rate was performed in the electrophysiology laboratory immediately before and immediately after RF ablation in 64 patients with supraventricular tachycardia. Ablation targets in these 64 patients included the fast AV nodal pathway (n = 3), the slow AV nodal pathway (n = 14), a posteroseptal accessory pathway (n = 23), and a left lateral accessory pathway (n = 24). A control group of 21 patients undergoing diagnostic study but not ablation underwent identical analysis immediately before and at the conclusion of their procedure. Patients undergoing ablation also had time and frequency domain analysis performed on ambulatory 24-hour Holter tapes recorded before ablation and at 1 day, 1 month, and 6 months after ablation. Compared with preablation values, time domain analysis immediately after ablation revealed a significant increase in mean heart rate and significant reductions in heart rate variability expressed as SD, MSSD, and PNN50 in patients undergoing AV nodal modification or posteroseptal accessory pathway ablation. Frequency domain analysis revealed marked attenuation of high frequency (0.15 to 0.40 Hz) components, indicating parasympathetic denervation. These acute changes were not seen after ablation of left lateral accessory pathways or after diagnostic study without ablation. Time and frequency domain analysis of 24-hour ambulatory Holter monitors performed serially after ablation revealed resolution of abnormalities of heart rate and of heart rate variability 1 to 6 months after ablation, with reappearance of the high frequency parasympathetic component suggestive of reinnervation. RF ablation in the anterior, mid, and posterior regions of the low interatrial septum may disrupt preganglionic or postganglionic parasympathetic fibers located in these regions that are destined to innervate the sinus node. Such fibers become more scarce along the left AV groove with increasing distance from the posteroseptal space. Parasympathetic denervation may be one mechanism for persistent inappropriate sinus tachycardia after RF ablation.

Electrocardiographs abnormalities after radiofrequency catheter ablation of accessory bypass tracts in the Wolff-Parkinson-White syndrome

Repolarization abnormalities on surface electrocardiograms have been described after loss of ventricular preexcitation in some patients with the Wolff-Parkinson-White syndrome. Radiofrequency catheter ablation of overt accessory pathways provides a unique opportunity to study this phenomenon. In this study, serial electrocardiograms were obtained before and after radiofrequency ablation of manifest accessory pathways in 19 patients, of concealed accessory pathways in 6 and after radiofrequency atrioventricular nodal modification in 12. Seven patients undergoing manifest right-sided accessory pathway ablation had left superior frontal plane T-wave axis deviations after ablation (−42 ± 13 °). No patient with a manifest left-sided or concealed accessory pathway, or atrioventricular nodal modification had T-wave abnormalities after ablation; however, left anterior fascicular block and incomplete right bundle branch block each occurred in 1 patient with left accessory pathway ablation. Repolarization abnormalities observed after ablation were similar to T-wave abnormalities during the absence of preexcitation before ablation and persisted up to 5 weeks after the procedure. Patients with repolarization abnormalities after ablation had significantly longer preexcited QRS durations than those without such changes, suggesting that the initial contribution of the pathway to ventricular activation is an important determinant of T-wave changes after ablation. The proposed mechanism for repolarization abnormalities after ablation is the phenomenon of T-wave “memory”.

Persistent inappropriate sinus tachycardia after radiofrequency current catheter modification of the atrioventricular node

Atrioventricular (AV) junctional reentrant tachycardia (JRT) is the most frequent cause of paroxysmal supraventricular tachycardia. 1 Recently, radiofrequency current delivered through a transvenous catheter was used to modify AV nodal properties so that AVJRT is no longer inducible while preserving normal AV nodal conduction. 2–4 This technique has produced high success rates with relatively few complications. In this report, we present a previously unreported complication observed in 3 patients undergoing AV node modification using radiofrequency current: persistent, inappropriate and symptomatic sinus tachycardia.

Percutaneous radiofrequency catheter ablation for supraventricular arrhythmias in children

Nineteen procedures were performed in 17 children, aged 10 months to 17 years, using catheter radiofrequency applications for the management of malignant or drug-resistant supraventricular tachyarrhythmias. Diagnoses were junctional ectopic tachycardia in 1 patient, atrioventricular (AV) node reentrant tachycardia in 4 and accessory pathway-mediated tachycardia in 12. Accessory pathway locations were left lateral (n = 4), posteroseptal (n = 3), left posterior (n = 2), right posterolateral (n = 1), right posterior paraseptal (n = 1), right intermediate septal (n = 1) and right anterior (n = 1).Ablation of accessory pathways was performed using 20 to 40 W of energy. The catheter was passed retrograde to the left ventricle in patients with a left-sided pathway and anterograde to the right atrium in those with a right-sided or posteroseptal pathway. In the 12 patients with an accessary pathway, radiofrequency applications were successful in 11 pathways and failed in 2. There were no recurrences of accessory pathway-mediated tachycardia.Atrioventricular node reentrant tachycardia was treated by AV node modification using 15 W of energy applied until first degree AV block occurred. After radiofrequency catheter ablation, there was a prolonged AH interval, tachycardia was not inducible and tachycardia recurred in one patient. For the patient with junctional ectopic tachycardia, 15 to 18 W of energy was delivered at the site of the maximal His bundle electrogram until sinus rhythm and normal AV conduction appeared. After a recurrence, a second procedure abolished tachycardia and AV conduction.In summary, radiofrequency catheter ablation was initially successful in 17 of 19 procedures and ultimately curative in 14 (82%) of 17 patients with no serious complications. Radiofrequency catheter ablation appears to be a safe and effective method for the management of supraventricular tachyarrhythmias in children.

Indications for modification of coexisting dual atrioventricular node pathways in patients undergoing surgical ablation of accessory atrioventricular connections

Concomitant susceptibility to atrioventricular (AV) node reentrant tachycardia has been demonstrated in certain patients having reentrant tachycardia utilizing accessory AV connections. For those patients undergoing accessory connection ablation, AV node surgical modification may be warranted during the same operative procedure. To assess indications for a combined operative procedure, this study evaluated potential predictors of subsequent spontaneous AV node reentrant tachycardia in patients undergoing ablation of accessory AV connections.Among 62 consecutive patients undergoing surgical ablation of an accessory AV connection, 13 (21%) manifested dual AV node pathways. The latter were identified preoperatively in five patients (four with concealed and one with bidirectional accessory connections) and postoperatively in seven (all seven with bidirectional accessory connections). In one patient with a bidirectional accessory connection, dual AV node pathways could not be demonstrated preoperatively, but AV node reentrant tachycardia was induced. Operative ablation of an accessory connection was successful in all patients. However, postoperatively, 2 of the 13 patients had inducible AV node reentrant tachycardia, 5 had AV node “echo” beats and 6 had no inducible arrhythmia.During 26 ± 7 months of follow-up study, the two patients with inducible AV node reentrant tachycardia postoperatively had symptomatic AV node reentrant tachycardia. In addition, the one patient with inducible AV node reentrant tachycardia preoperatively had recurrence of this tachycardia 4 months after attempted surgical modification of the AV node. Consequently, although dual AV node pathways appear to be common in patients undergoing surgical ablation of an accessory AV connection (21%), only a small group (3 of 13) of these patients are at risk for subsequent clinical AV node reentrant tachycardia.The presence of dual AV node pathways either alone or in conjunction with AV node echoes does not predict occurrence of AV node reentrant tachycardia. However, induction of sustained AV node reentrant tachycardia appears to be associated with a greater likelihood of spontaneous symptomatic tachycardia and therefore warrants consideration of AV node modification at the time of surgical ablation of an accessory connection.

Electrophysiologic characteristics of manifest and latent retrograde conduction in dogs

Atrioventricular (AV) nodal reentry requires intact retrograde ventriculoatrial (VA) conduction. The purpose of this study was to assess the contribution of various pacing and pharmacologic techniques to uncover VA conduction during apparent unidirectional VA block, and to evaluate the role of several biologic and electrophysiologic factors in concealment of retrograde conduction. Forty healthy dogs underwent catheter-electrophysiologic studies of AV and VA conduction. Group I (20 animals) had intact VA conduction. Group II (six animals) had VA dissociation with ventricular pacing initiated during sinus rhythm, but the presence of VA conduction was confirmed by isoproterenol infusion or by premature ventricular stimulation. In group III (14 animals), the above techniques failed to uncover VA conduction. Eight of 14 group III animals underwent thoracotomy and crushing or freezing of the sinoatrial (SA) node. Ventricular pacing initiated during sinus standstill was associated with 1:1 VA conduction in each experiment. VA conduction time and retrograde Wenckebach cycle length, both in the baseline state and during isoproterenol infusion, were significantly longer in the eight animals in group III than in those in group I. Age, gender, weight, breed, sinus cycle length, and anterograde AV conduction properties were not significantly different between groups I, II, and III. The data suggest that (1) in normal dogs, complete unidirectional VA block probably does not exist; (2) in the presence of anterograde input to the AV node, even sophisticated pacing and pharmacologic maneuvers may fail to uncover the presence of VA conduction; (3) although anterograde input is essential for concealment of VA conduction, the phenomenon is more closely associated with depressed retrograde than with anterograde AV nodal characteristics. These data may be important when analyzing the effects of various AV nodal modification procedures on the apparent elimination of VA conduction.

Percutaneous catheter modification of the atrioventricular node. A potential cure for atrioventricular nodal reentrant tachycardia.

Our purpose was to describe a technique of atrioventricular (AV) node modification for patients with drug refractory AV nodal reentrant tachycardia (AVNRT). Nine patients (mean age, 45 +/- 20; range, 14-82) with recurrent drug refractory AVNRT (n = 8) or sudden cardiac death thought to be precipitated by AVNRT (n = 1) underwent a percutaneous catheter procedure to modify AV nodal function. The area between the electrode recording the maximal His-bundle electrogram and the ostium of the coronary sinus was divided into three zones. Perinodal direct current shocks of 100-300 J were delivered to one (n = 2), two (n = 3), or three (n = 4) zones without complications. The procedure endpoints were modification of AV conduction (either first degree AV block or complete retrograde ventriculo-atrial [VA] block) and failure to induce AVNRT before or after isoproterenol and/or atropine administration. Six of nine patients (67%) have had no inducible or spontaneous AVNRT over a mean follow-up of 12.3 +/- 4.1 months (range, 4.5-17). One of the six underwent repeat, successful modification, because AVNRT was inducible at restudy 2 days after the initial procedure. AVNRT recurred in three patients (33%), one early (3 days) and two late (3-4 months). Two of these patients underwent complete ablation of the AV junction and permanent pacemaker placement, whereas one is controlled with drug therapy. Therefore, AV nodal modification resulted in tachycardia control without antiarrhythmic drugs in six of nine (67%) and obviated the need for complete AV junctional ablation in seven of nine patients (78%). Elimination of AVNRT appears to result from either block in the retrograde fast pathway or modification of the antegrade slow pathway, such that AVNRT cannot be sustained. Additional findings suggest that an atrio-Hisian accessory connection may not be involved in AVNRT in some of these patients. Percutaneous catheter AV nodal modification appears to be a promising technique for treatment of refractory AVNRT and may obviate need for complete AV junctional ablation in a substantial number of patients with drug/pacemaker refractory AVNRT.