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Optimum arrhythmia management has evolved to couple ICD therapy with catheter ablative and drug therapy to attempt to eliminate or reduce arrhythmia risk. No longer should the clinician approach such therapy as a choice among single alternative strategies only. Optimum patient management includes not only recognition of the indications and benefits of such hybrid therapy but also a complete understanding of potential pitfalls of such therapy.

Background: Radiofrequency (RF) catheter ablation is effective therapy for monomorphic ventricular tachycardia (VT) in patients without structural heart disease. In patients with postinfarction VT; however, this procedure has been used predominantly as adjunctive therapy, targeting only the patient's clinically documented arrhythmia. By targeting all inducible, sustained VT morphologies, we sought to determine the utility of RF catheter ablation as a primary cure in patients who present with hemodynamically tolerated VT., Methods and Results: RF ablation was attempted in 35 patients with a previous myocardial infarction and recurrent, hemodynamically tolerated VT. A mean of 3.9+/-2.7 VTs were induced per patient (range, 1 to 10). The clinically documented arrhythmia was successfully ablated in 30 of 35 patients (86%), and on follow-up electrophysiological testing, 11 patients had no inducible VT and were discharged without other therapy. Nineteen patients had inducible "nonclinical" arrhythmias on follow-up testing, and the majority underwent cardiac defibrillator implantation. Freedom from recurrent arrhythmias, including sudden death, was 91% in patients without inducible VT and 53% in patients with persistently inducible "nonclinical" arrhythmias (P<.05; mean follow-up, 17+/-12 and 12+/-11 months, respectively)., Conclusions: In patients with well-tolerated VT, RF catheter ablation may be useful as a primary cure if no other ventricular arrhythmias are inducible on follow-up testing. Ablation of all hemodynamically tolerated arrhythmias should be attempted in patients with multiple inducible VT morphologies because of the high rate of recurrence of unablated VTs in these patients.

Many ICD devices have the capability for back up bradycardia pacing. Because of the use of a single sensing algorithm for both bradycardia and tachycardia functions, they may be prone to certain "sensing errors." Following implantation of an ICD in a patient with long QT syndrome, "inappropriate" pauses were noted during bradycardia pacing, which were exactly twice the programmed pacing cycle length. This was due to an automatic increase in the device's sensitivity during pacing, a characteristic of the automatic gain control of this particular ICD. Proper recognition of this ICD's special features, known as "lower threshold crossing," allowed noninvasive rectification of the problem and prevented these pauses.

Introduction: Isoproterenol is used to assess and facilitate AV nodal conduction, and thus potentiate the induction of supraventricular arrhythmias. It is commonly administered in increasing doses until a predetermined decrease in sinus cycle length, usually 20% to 30%, occurs. This regimen may result in undesirable side effects. We have observed that effects of isoproterenol on the AV node may occur prior to achieving the target sinus cycle length. The purpose of this study was to determine whether the sinus and AV nodes have equal sensitivity to isoproterenol., Methods and Results: Thirty-eight consecutive patients, who underwent electrophysiologic evaluation for a variety of indications, were given incremental doses of isoproterenol at 0.007, 0.014, 0.021, and 0.028 microgram/kg per minute. Sinus cycle length and AV node function were assessed at baseline and after 5 minutes at each dose. The percent change from baseline in AV node function was compared with the change in sinus cycle length at each dose interval. Significantly greater decreases were observed in the anterograde and retrograde AV nodal Wenckebach cycle length (P < 0.0001) than in the sinus cycle length at the lowest isoproterenol dose (0.007 microgram/kg per min). These differences were not apparent at higher doses. A sustained supraventricular tachycardia was inducible in 15 of 38 patients in the presence of isoproterenol, of which 40% occurred at the lowest dose., Conclusions: The AV node is more sensitive than the sinus node to the effects of isoproterenol. Lower doses of isoproterenol than those commonly used may often facilitate the induction of a supraventricular tachyarrhythmia, thus reducing side effects.

Background: Bradycardia and sinus node dysfunction are common causes of early postoperative morbidity in orthotopic heart transplant recipients and frequently require the use of chronotropic drugs or permanent pacemakers. Several causes have been postulated, including surgical trauma to the sinus node and its blood supply. We sought to eliminate sinus node dysfunction and postoperative bradyarrhythmias by altering the orthotopic heart transplantation technique., Methods and Results: Seventy orthotopic heart transplant recipients underwent electrophysiological testing of sinus node function a mean of 9 +/- 3 days after surgery. Standard (atrial anastomosis) orthotopic heart transplantation was performed in 33 patients; total (bicaval anastomosis) heart transplantation was performed in 37 patients. Abnormalities of sinus node function were present in 14 of 33 patients (42%) undergoing standard orthotopic heart transplantation compared with 2 of 37 patients arrhythmia (5%) in whom total heart transplantation was performed (P < .005). The resting sinus heart rate of patients with a normal sinus rhythm was also significantly higher in the total heart transplantation group (90 +/- 12 versus 83 +/- 14 bpm, P < .05). Coronary angiography was performed before discharge in 63 patients. Eleven were found to have an abnormal sinoatrial nodal artery, and 7 of these patients also had evidence of sinus node dysfunction (P < .005)., Conclusions: Surgical trauma to the donor sinus node and/or its blood supply is a significant cause of sinus node dysfunction in the orthotopic heart transplant recipient. By use of a bicaval anastomotic technique, the incidence of and need for treatment of postoperative bradyarrhythmias can be significantly reduced.

Direct treatment of atrial flutter and atrial fibrillation--that is, attempting to prevent arrhythmia recurrences by ablating atrial tissue--has been a challenge because of uncertainty about the location of optimal target tissues as well as the amount of atrial tissue requiring destruction to effect cure. Advances have yielded success rates for ablation of the common form of atrial flutter comparable to those for other types of supraventricular tachycardia and provide reason for optimism about the use of catheter techniques, to treat atrial fibrillation definitively. This article discusses some of these advances as well as the current status of catheter ablation for atrial flutter and atrial fibrillation and, finally, what the future may bring.

The efficacy of antitachycardia pacing (ATP) incorporated into implantable cardioverter defibrillators (ICDs) was assessed in 29 consecutive survivors of cardiac arrest, not attributable to acute myocardial infarction, ischemia, or drug and electrolyte effects. The cohort included 25 men and 4 women with a mean age of 65 years and a mean left ventricular ejection fraction of 29%. Seventeen patients had coronary artery disease, 11 had nonischemic dilated cardiomyopathy, and 1 had long QT syndrome. Programmed stimulation yielded monomorphic ventricular tachycardia (VT) in 17 patients, polymorphic VT in 6, and no inducible VT in 6. During a mean follow-up of 22 months, a total of 91 episodes of monomorphic VT occurred, 73 of which were successfully pace terminated (83%). Monomorphic VT amenable to pace termination recurred only in the group that had this arrhythmia inducible. The recurrent arrhythmias in the 12 patients having either no inducible VT or polymorphic VT were all rapid VTs, having a cycle length < 220 ms; and therefore, not amenable to pace termination. These results suggest that ATP incorporated into ICDs is useful in survivors of cardiac arrest and may significantly reduce the number of shocks that these patients would otherwise receive. Programmed stimulation may also help to define those patients who would receive the maximum benefit from ATP.

Interatrial conduction of recipient atrial tachycardia to the donor atria of an orthotopic heart transplant recipient resulted in a unique cause of supraventricular tachycardia. An electrophysiologic study was performed, and the recipient atria was found to be in an atrial tachycardia, cycle length of 210 msec, with periods of both 2:1 and 1:1 conduction to the donor atria resulting in a donor atrial cycle length of 420 msec and 210 msec, respectively. The site of interatrial conduction was mapped to the right atrial suture line, along the atrial free wall, and was successfully disrupted with radiofrequency energy. Arrhythmias of a similar mechanism may also be observed in other postsurgical patients.

Background: Sinus node dysfunction has been reported to occur in up to 50% of orthotopic heart transplant recipients, and oral theophylline has been used in an attempt to limit the morbidity associated with this abnormality. The purpose of this study was to evaluate the electrophysiologic effects of methylxanthines on sinus node function., Methods: Sinus node testing performed in 26 patients before and after the infusion of 6 mg/kg of aminophylline. Thirteen of these patients had abnormal sinus node function at baseline, and thirteen had normal sinus node function. Sinus node dysfunction was diagnosed by a rhythm other than sinus in five patients, a prolonged corrected sinus node recovery time in two patients, and the presence of a secondary pause in six patients., Results: In patients with abnormal sinus node function a significant decrease was observed in the sinus node recovery time (-14% +/- 5%) and corrected sinus node recovery time (-33% +/- 25%) in response to aminophylline; however, neither parameter was normalized. A decrease in the sinus cycle length (-6% +/- 8%) was not statistically significant. In patients with normal sinus node function, a significant decrease was seen in both the sinus node recovery time (-9% +/- 7%) and sinus cycle length (-9% +/- 4%). The corrected sinus node recovery time decreased by 4% +/- 28% in patients with normal conditions but was not significant. Overall, aminophylline resolved the underlying sinus node abnormality in only one of thirteen patients with abnormal sinus node function., Conclusions: This study suggests that the use of theophylline in patients with marked sinus node dysfunction may not decrease their risks for subsequent bradycardic events.

Introduction: A male patient with an atriofascicular pathway underwent catheter ablation of the atriofascicular pathway during atrial fibrillation., Methods and Results: The patient had preexcited atrial fibrillation both clinically and repeatedly during electrophysiologic study. A preexcited tachycardia with a 1:1 AV relationship and regular RR intervals was also induced. Catheter ablation of the atriofascicular pathway could only be performed during persistent atrial fibrillation, based on mapping of the pathway's insertion into the right bundle branch. Following successful ablation and cardioversion to sinus rhythm, a regular QRS tachycardia (atrioventricular [AV] nodal reentry) having the same rate, atrial activation sequence, and His-atrial time as the regular preexcited tachycardia noted preablation was initiated. An AV nodal slow pathway modification eliminated this tachycardia. Neither atrial fibrillation nor AV nodal reentry has recurred on follow-up., Conclusion: This is the first report of atriofascicular mapping and ablation performed exclusively during atrial fibrillation and illustrates the utility of mapping the pathway's ventricular insertion. Other unusual features ("bystander" pathway activation during AV nodal reentry, possible role of the pathway in genesis of atrial fibrillation) are discussed.

Orthotopic heart transplantation was performed in a 65-year-old man with a donor heart with Wolff-Parkinson-White Syndrome. An electrophysiologic study performed 7 days after transplantation showed a left-lateral accessory pathway that exhibited only anterograde conduction. Radiofrequency ablation of the bypass tract was successfully performed, and no evidence of recurrence was found at 12 months' follow-up. We suggest that potential donors with known electrophysiologic abnormalities that are amenable to catheter ablation techniques should be considered for orthotopic heart transplantation, thus broadening the potential donor pool.

The defibrillation threshold (DFT) using simultaneous (SIML) versus sequential (SEQ) pathways for shock delivery was compared in 16 patients with an implanted cardioverter defibrillator. All patients had three-lead nonthoracotomy systems (NTL) using a left chest subcutaneous patch, a right ventricular endocardial lead, and a lead in the coronary sinus (n = 5) or superior vena cava (n = 11). The DFT were determined 2-44 days (17 +/- 17 days) after implantation. The DFT was defined as the lowest energy shock that resulted in successful defibrillation. The first pathway tested was SIML in 12 and SEQ in 4 patients with output beginning at or above the intraoperative DFT, routinely 18 J. The second pathway was tested beginning 2-4 J above the DFT of the first tested pathway. All shocks were delivered in 2-4 J decrement or increment steps. The SEQ pathway shocks resulted in a significantly lower DFT than SIML pathway shocks (14 +/- 6 vs 18 +/- 6 J; P < 0.01). There was no difference in the time delay after ventricular fibrillation initiation before shock delivery for the successful defibrillation between SIML versus SEQ pathways (7 +/- 2 secs for both pathways). In 7 of 16 patients, defibrillation using SEQ pathway resulted in a > 5 J lowering of DFT, while only one patient had > 5 J lowering of DFT using SIML shocks (P < 0.05). These results have important implications for selecting the optimal pathway for implantable cardioverter defibrillator therapy with a multilead NTL system.

The stability of the defibrillation threshold (DFT) early after implantation of an implantable cardioverter defibrillator was evaluated in 15 patients. All but one patient had a three lead nonthoracotomy system using a subcutaneous patch, a right ventricular endocardial lead, and a lead in coronary sinus (n = 5) or superior vena cava (n = 9). Shocks were delivered using simultaneous in nine, sequential in three, and single pathway (coronary sinus not used) in one patient. DFTs were measured at implant (n = 15), 2-8 days postoperation (postop, n = 15), and 4-6 weeks later (n = 8). The DFT was defined as the lowest energy shock that resulted in successful defibrillation. The DFT was assessed with output beginning at 18 joules or 2-4 joules above the implant DFT. All shocks were delivered in 2- to 4-joule increments or decrements. DFTs were significantly higher postoperatively than DFTs at implant (22.7 +/- 7.0 J vs 16.9 +/- 3.9 J; P < 0.05). Eight of 15 patients had DFT determined at all three study periods. In these patients, DFT increased at postop (22.8 +/- 8.3 J vs 16.4 +/- 3.9 J at implant; P < 0.05) and returned to baseline at 4-6 weeks (16 +/- 7.1 J vs 16.4 +/- 3.9 J at implant; P = N.S.). Thus, in patients with a multilead nonthoracotomy system, a DFT rise was observed early after implant. The DFT appears to return to baseline in 4-6 weeks. These results have important implications for programming energy output after implantable cardioverter defibrillator implantation.

The approach to patients with hemodynamically-stable sustained monomorphic ventricular tachycardia (VT) must be individualized. The clinical outcome is critically dependent on the type and degree of underlying heart disease, symptoms at presentation, inducibility at electrophysiology study, and responses to antiarrhythmic drugs. Various methods for assessing therapeutic efficacy and both pharmacologic and nonpharmacologic therapies are discussed. The majority of patients with nonsustained VT have no symptoms directly attributable to this arrhythmia that is associated with an increased risk for sudden death in certain patients with coronary artery disease and hypertrophic cardiomyopathy. The optimal means to prophylax against sudden death in these patients is not presently clear, but prospective trials are underway to evaluate this problem.

To determine whether the asynchronous left ventricular contraction-relaxation sequence that exists during right ventricular pacing alters left ventricular relaxation, measurements of both the maximal rate of decline of left ventricular pressure (peak negative dP/dt) and the time constant of left ventricular relaxation were obtained during atrial and atrioventricular (AV) pacing in 25 patients referred for diagnostic cardiac catheterization. Heart rate was maintained at 10 to 15 beats/min above the sinus rate at rest, and relaxation was assessed during atrial pacing, AV pacing and repeat atrial pacing. The patients were classified into two groups. Group 1 included 10 patients with normal left ventricular systolic function at rest (ejection fraction greater than 0.55) and without evidence of prior myocardial infarction. Group 2 included 15 patients with a depressed left ventricular ejection fraction or akinesia of one or more left ventricular segments on the contrast ventriculogram, or both. Heart rate, peak left ventricular systolic pressure, end-systolic pressure and end-diastolic pressure remained constant during atrial, AV pacing and repeat atrial pacing in all patients. In group 1 patients, the decrease in peak negative dP/dt (1,507 +/- 200 versus 1,424 +/- 187 mm Hg/s) and the increase in the time constant of left ventricular relaxation (48 +/- 11 versus 51 +/- 11 ms) during AV pacing was not significantly different when compared with values during atrial pacing.(ABSTRACT TRUNCATED AT 250 WORDS)