The effect of variable retrograde penetration on dual AV nodal pathways: observations before and after slow pathway ablation LDD

Retrograde VA conduction is usually over the fast pathway and rarely over the slow pathway in patients with dual AV nodal pathways. It is unknown whether this apparent unidirectional conduction of the slow pathway is due to the lack of its retrograde conducting ability or the result of concealment. The effect of variable retrograde AV nodal penetration on antegrade AV nodal conduction was determined in patients with typical AV nodal reentrant tachycardia before and after the slow pathway ablation. Variable retrograde penetration was produced by delivering a ventricular extrastimulus simultaneously with (VE-0), 50 ms after (VE-50), or 100 ms after (VE-100) the last basic atrial stimulus, while atrial extrastimuli were used to determine changes of anterograde AV nodal effective refractory period (ERP) and A-H interval. The AV nodal functions measured without the ventricular extrastimuli served as the baseline. Although the mean slow pathway ERP was not significantly different among the different stimulation protocols, a significant shortening of the slow pathway conduction time (A-H from 348 +/- 60 to 324 +/- 119 ms, P < 0.05) was observed with upper level retrograde penetration of the AV node (VE-0). This facilitating effect became a prolonging effect when the retrograde penetration level moved to the lower level (VE-100, A-H from 324 +/- 119 to 366 +/- 122 ms, P < 0.05). The fast pathway ERP shortened with an upper level penetration (VE-0) but tended to prolong with a lower level retrograde-penetration (VE-100) both before and after the slow pathway ablation (preablation, from 348 +/- 143 of the baseline to 302 +/- 114 to 360 +/- 143 ms, P < 0.05; postablation, from 314 +/- 101 of the baseline to 274 +/- 118 to 361 +/- 143 ms, P < 0.05). The mean A2-H2 interval of the slow pathway was significantly shorter than the baseline (350 +/- 44 ms) with VE-0 (249 +/- 48 ms, P < 0.05) and VE-50 stimulation (285 +/- 82 ms, P < 0.05) but not with VE-100 stimulation (330 +/- 83 ms, P = NS). Before slow pathway ablation, the A2-H2 interval of the fast pathway at equal coupling intervals was shorter than the baseline (165 +/- 53 ms) with VE-0 (144 +/- 47 ms, P < 0.01) and VE-50 stimulation (152 +/- 43 ms, P < 0.05) but tended to be longer with VE-100 stimulation (175 +/- 47 ms, P = NS). After slow pathway ablation, the mean A2-H2 interval at the same coupling interval was shorter than the baseline (173 +/- 39 ms) with VE-0 (139 +/- 35 ms, P < 0.05), VE-50 (153 +/- 32 ms, P = 0.05) but tended to be longer with VE-100 stimulation (178 +/- 49 ms, P = NS). We conclude that: (1) concealed retrograde conduction can be demonstrated in both the slow and the fast AV nodal pathways; and (2) concealed retrograde conduction may either shorten or prolong anterograde refractoriness and conduction time, depending on the level of retrograde penetration.

Management of mobile right atrial thrombi: a therapeutic dilemma

BACKGROUND

Mobile right atrial thrombus is an uncommon finding on two-dimensional (2D) echocardiography. Therapeutic alternatives include systemic heparinization, systemic or local thrombolysis, and surgical removal. We report our clinical experience in six patients over a 3-year period (6000 echocardiograms) at a tertiary care referral center.

METHODS

There were four men and two women with a mean age of 63 years (range: 47 to 73 years). Indications for echocardiography consisted of progressive dyspnea and chest pain in five patients and syncope with chest pain in one patient.

RESULTS

All were observed to have a mobile thrombus in the right atrium. Ventilation perfusion (V/Q) scanning confirmed V/Q mismatch in all patients. Subsequent echocardiography (minutes to 1 day later) in three patients demonstrated absence of the thrombus suggesting pulmonary embolization. One patient died during transesophageal echocardiography (TEE) and autopsy confirmed a large pulmonary embolization in the main pulmonary artery. Treatment consisted of heparinization in 3 patients, systemic thrombolysis in 1 patient, and surgical removal of the thrombus in 1 patient. At surgery, a long serpiginous thrombus was seen in the right atrium, tethered to a fenestrated eustachian valve. There were 3 deaths: 1 patient treated with heparin; 1 patient treated with thrombolysis; and 1 during TEE. Two of the three patients treated with heparin and one patient undergoing surgical removal survived hospitalization.

CONCLUSIONS

Mobile thrombus in the right atrium is an unusual echocardiographic finding. It portends a poor prognosis with death due to pulmonary embolism.

Cardiac manifestations of Lyme disease: a review

OBJECTIVE

To describe the clinical features of cardiac manifestations of Lyme disease, the most common vector-borne illness in North America, which occasionally results in cardiac involvement.

DATA SOURCES

A review of the English-language clinical literature pertaining to Lyme disease and Lyme carditis indexed in MEDLINE from 1975 to 1995.

DATA EXTRACTION

Studies describing diagnosis, clinical features, treatment or outcome were reviewed.

DATA SYNTHESIS

Cardiac complications of Lyme disease may occur in up to 8% of patients. Cardiac manifestations occur in the early phase of the illness, at a median of 21 days from the onset of erythema migrans. Manifestations of Lyme carditis include atrioventricular block, myopericarditis, intraventricular conduction disturbances, bundle branch block and congestive heart failure. Temporary cardiac pacing may be required in up to a third of cases and complete recovery occurs in most (greater than 90%) patients. The overall prognosis of Lyme carditis is very good, although recovery may be delayed and late complications such as dilated cardiomyopathy may occur.

CONCLUSION

Lyme disease is a tick-borne spirochetal infection caused by Borrelia burgdorferi. Cardiac complications of Lyme disease generally occur in the early phase and include conduction system disturbances, myopericarditis and congestive heart failure.

Anatomic substrate for idiopathic left ventricular tachycardia

BACKGROUND

Idiopathic left ventricular tachycardia (ILVT) characterized by QRS complexes with right bundle-branch block (RBBB) morphology and left axis deviation is a distinct clinical syndrome that also demonstrates a characteristic response to verapamil and inducibility from the atrium in patients without structural heart disease. A false tendon has been described in the left ventricle in a patient with ILVT in whom surgical resection of the false tendon resulted in cure. We hypothesized that the false tendon is responsible for the genesis of similar ventricular tachycardia (VT) in others.

METHODS AND RESULTS

We performed transthoracic (TTE) and/or transesophageal (TEE) two-dimensional echocardiograms in 15 patients undergoing catheter ablation for ILVT. There were 12 men and 3 women (mean age, 31 +/- 12 years, with average symptom duration of 11 +/- 9 years). The mean VT cycle length was 360 +/- 70 ms, and all had RBBB morphology with left axis deviation. Cardiac chamber sizes, left ventricular wall thickness, and wall motion were normal in all ILVT patients. TTE and/or TEE demonstrated a false tendon extending from the posteroinferior left ventricular free wall to the left ventricular septum in all ILVT patients. The false tendons were thick (> or = 2 mm maximal thickness) in 5 patients and thin (< 2 mm maximal thickness) in 10 patients. We compared ILVT patients with a control group of 671 consecutive patients referred for echocardiography for other reasons. The mean age for the control group was 42 years. A false tendon was seen in the left ventricle in 34 of 671 (5%). In the control group patients with a false tendon, 2 patients had a history of VT (left bundle-branch block morphology) and 1 had ventricular fibrillation. The false tendons in the control patients were also oriented transversely across the ventricular cavity but were somewhat thinner (< 2 mm maximal thickness in 32 of 34 patients). Catheter ablation with the use of radiofrequency and/or direct current applied to the posteroapical septum resulted in cure in 14 of 15 patients.

CONCLUSIONS

A false tendon extending from the posteroinferior left ventricle to the septum is a consistent finding in patients with ILVT and probably is responsible for this unique arrhythmia. The mechanism by which the false tendon precipitates tachycardia is speculative, but possibilities include conduction through the false tendon or by producing stretch in the Purkinje fiber network on the interventricular septum.

Circadian variation in sudden cardiac death: effects of age, sex, and initial cardiac rhythm

STUDY OBJECTIVE

Previous studies based on data obtained from vital statistics records have demonstrated circadian variation in the occurrence of sudden cardiac death. The purpose of this study was to examine the effects of age, sex, and initial cardiac rhythm on circadian variability in sudden cardiac death.

METHODS

This study employed a retrospective analysis of the records of adult patients with witnessed cardiac arrest who underwent resuscitation in an urban paramedic system during a 5-year period.

RESULTS

The records of 2,250 consecutive patients with witnessed cardiac arrest were reviewed. Spectral analysis was used to decompose the data into frequency components. A circadian variation in the occurrence of sudden cardiac death was demonstrated, with a low occurrence rate between midnight and 6 AM and a 2.4-fold increase between the rate at 6 AM and the rate at noon. The same circadian pattern was noted among both men and women, among both patients aged 18 to 70 and those older than 70 years, and among patients with various initial cardiac arrest rhythms (ventricular tachycardia or fibrillation, asystole, and electromechanical dissociation). However, the outcome of resuscitation in these patients (ie, the rate of successful resuscitation and the rate of survival) did not demonstrate circadian variation.

CONCLUSION

Witnessed out-of-hospital sudden cardiac death demonstrated circadian variation, and this variability was observed regardless of the patient's age, sex, or initial cardiac arrest rhythm. The outcome of resuscitation did not show circadian variability. These results suggest a common pathophysiologic mechanism leading to sudden cardiac death.

Latissimus dorsi dynamic cardiomyoplasty: role of combined ICD implantation

Latissimus dorsi cardiomyoplasty is a promising surgical therapy in some patients with congestive heart failure. Although the mortality in heart failure patients is attributable primarily to heart failure and ventricular arrhythmias, the mechanism of death after cardiomyoplasty is not well characterized. We describe the clinical course of a patient undergoing cardiomyoplasty and discuss the role of combined use with an implantable cardioverter defibrillator. A 39-year-old man with congestive heart failure due to a massive anterior wall myocardial infarction was evaluated for latissimus dorsi cardiomyoplasty. The patient was in NYHA Functional Class III due to heart failure. He did not have any significant exertional or rest angina. During a Naughton stress test, the patient could exercise for 10 minutes, achieving 4 METS. Pulmonary function study showed a peak V O2 of 22.1 mL/min per kg. Radionuclide angiography demonstrated that the anterior wall was akinetic with a left ventricular ejection fraction of 22%. Cardiac hemodynamic studies suggested moderate pulmonary hypertension, elevated wedge pressure, and suboptimal response to exercise. A Holter recording showed frequent ventricular extrasystoles. Cardiomyoplasty was preferred to heart transplantation because the patient did not have end-stage heart failure. Postoperatively, the patient required low doses of dopamine. He developed recurrent, sustained, and hemodynamically significant episodes of ventricular tachycardia. He was treated with a combination of amiodarone and procainamide. He died 2 days postoperatively with ventricular fibrillation. Ventricular arrhythmias are a major cause of death in patients with heart failure. Latissimus dorsi cardiomyoplasty appears to be a promising but unproven therapy in such patients.(ABSTRACT TRUNCATED AT 250 WORDS)

Itraconazole versus griseofulvine in the treatment of tinea corporis and tinea cruris

126 patients (82 males and 44 females) aged above 12 years, suffering from tinea corporis and/or tinea cruris, were treated with either itraconazole (100 mg once a day for 2 weeks and then plecebo for 2 weeks) (63 patients), or griseofulvin (250 mg twice a day for 4 weeks). 90.47% of the patients treated with itraconzole improved whereas griseofulvin imporved 76.19% of patients, clinically. Mycological response was 72% with itraconazole and 57% with griseofulvin.

Catheter ablation of idiopathic left ventricular tachycardia

Idiopathic left ventricular tachycardia (ILVT) characterized by right bundle branch block, left axis morphology, response to verapamil and inducibility from the atrium in patients without structural heart disease may represent a distinct clinical entity. We report our experience with catheter ablation of this uncommon arrhythmia using radiofrequency energy (RF) and/or direct current (DC) shocks. Six men and 2 women, aged 16-50 years (mean +/- SD, 32 +/- 13), had recurrent VT for 16 +/- 16 years with a mean frequency of 4 +/- 3 episodes/year. Three patients had syncope during VT. None had identifiable structural heart disease. Catheter ablation was guided by earliest endocardial activation, presence of a high frequency presystolic potential and/or pacemapping of the left ventricle. The left ventricle was accessed via a retrograde aortic approach in 6 patients, a transeptal approach in 1 patient, and a combined approach in the remaining patient. All patients had inducible right bundle branch block morphology, left axis VT with a mean cycle length (CL) of 361 +/- 61 ms. A presystolic potential preceding ventricular activation and the His potential during VT was identified in 4 patients. All ablation sites were identified in a relatively uniform location, in the inferoapical left ventricle. Noninducibility of VT was obtained with RF in 3 patients and with DC in 5 patients. In 1 patient, DC delivery after unsuccessful RF prevented further inducibility. Similarly, RF was successful in 1 patient in whom an initial DC attempt was ineffective. Mean total procedure time was 282 +/- 51 minutes and mean total fluoroscopy time was 40 +/- 15 minutes. There were no complications. One patient treated with DC shock had recurrence of VT during treadmill test the day after ablation and refused repeat ablation. During a mean follow-up of 17 +/- 13 months, no VT recurrences or other cardiovascular events occurred. In conclusion, catheter ablation in the inferoapical left ventricle is an effective treatment for this type of ILVT. RF energy can be safely complemented by low energy DC shocks when the former is ineffective.

Effect of dual atrioventricular node pathways on atrioventricular reentrant tachycardia

BACKGROUND

Dual atrioventricular (AV) node pathway physiology is frequently observed in patients with AV accessory pathways.

METHODS AND RESULTS

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.

CONCLUSIONS

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.

Lyme carditis: indications for cardiac pacing

Lyme disease is a tick-borne illness caused by the spirochete Borrelia burgdorferi. It is the most common reported vector-borne illness in the United States. The clinical course of Lyme disease is divided into early and late phases. Early disease may be limited or disseminated. Generally, cardiac complications occur in the early disseminated phase. Disturbance of atrioventricular conduction is the most commonly recognized cardiac manifestation of Lyme disease. This is usually self-limited and does not require permanent cardiac pacing. A case of Lyme carditis with atrioventricular block requiring permanent pacing is reported and the indications for cardiac pacing in this disease are reviewed.

Subpectoral implantation of ICD generators: long-term follow-up

A nonthoracotomy surgical approach using an endocardial electrode and combined implantation of a subcutaneous patch and the implantable cardioverter defibrillator (ICD) generator in a subpectoral pocket has been described. We report the long-term follow-up results in patients undergoing implantation using this approach. The patient population consisted of 28 patients (22 men and 6 women) with a mean age of 59 +/- 12 years. The underlying heart disease consisted of coronary artery disease in 20 patients and dilated cardiomyopathy in 8 patients. Sustained ventricular tachycardia was the mode of presentation in 16 patients and sudden cardiac death in 12 patients. The mean left ventricular ejection fraction was 31% +/- 6%. The lead system consisted of an 8 French bipolar passive fixation rate sensing lead positioned at the right ventricular apex, an 11 French spring coil electrode positioned at the superior vena cava-right atrial junction (surface area 700 mm2), and submuscular placement of a large patch (surface area 28 cm2) on the anterolateral chest wall near the cardiac apex via a submammary incision. A defibrillation threshold of < or = 15 joules (J) was required for implantation. This criterion was not satisfied in five patients; thus, a limited thoracotomy was performed via the submammary incision, and the large patch was placed epicardially. The mean R wave amplitude was 12 +/- 3 mV, the mean pacing threshold was 1.0 +/- 0.5 V at 0.5 msec, and the mean defibrillation threshold was 12.6 +/- 3 J. ICD generators implanted were the Ventak-P in 17, PCD-7217 in 5, and the Cadence V-100 in 6 patients.(ABSTRACT TRUNCATED AT 250 WORDS)

A direct comparison of epicardial and nonthoracotomy defibrillation using monophasic and biphasic shocks

Defibrillation using epicardial patches may be associated with lower energy requirements than nonthoracotomy defibrillation although a direct comparison using various waveforms has not been reported. To directly compare defibrillation efficacy using these two configurations, nine mongrel dogs (20.9 +/- 2.3 kg) first underwent nonthoracotomy defibrillation testing followed by a thoracotomy and implantation of epicardial patch electrodes and redetermination of defibrillation efficacy. Each dog served as its own control. Nonthoracotomy electrode configuration consisted of a right ventricular catheter (cathode) and a chest wall subcutaneous patch (anode). The epicardial configuration consisted of two 13.9 cm2 epicardial patches. Alternating current induced ventricular fibrillation was allowed to persist for 10 seconds, followed by either a monophasic or a single capacitor biphasic shock of 10-msec total duration. Four trials of five leading edge voltages were performed for monophasic and biphasic pulses and stepwise logistic regression analysis was used to determine 80% probability of successful defibrillation (E80). For epicardial defibrillation E80s were: monophasic 19.2 +/- 4.2 J and biphasic 12.6 +/- 4.0 J; nonthoracotomy defibrillation E80s were: monophasic 24.2 +/- 4.4 J and biphasic 17.8 +/- 4.1 J. Epicardial patch defibrillation required less energy than nonthoracotomy electrode configuration. However, using biphasic pulses nonthoracotomy defibrillation could achieve lower defibrillation energy requirements than epicardial defibrillation with monophasic pulses.

Atypical retrograde atrial activation in 'typical' atrioventricular nodal reentrant tachycardia

Atrioventricular nodal reentrant tachycardia (AVNRT) can be cured by radiofrequency catheter ablation by selective ablation of the slow or the fast pathway. Retrograde fast pathway ablation is performed anterosuperiorly at the apex of Koch's triangle, whereas slow pathway ablation is performed at the base of Koch's triangle near the coronary sinus ostium. A patient with otherwise typical slow-fast AVNRT who demonstrated earliest retrograde atrial activation at the proximal coronary sinus rather than the usual His bundle recording position is described. Loss of retrograde fast pathway conduction occurred after radiofrequency ablation at the base of Koch's triangle, suggesting an atypical location of the fast pathway. This supports recent evidence that the retrograde fast pathway may be located near the coronary sinus ostium in some patients with otherwise typical AVNRT.

Ventriculoatrial conduction in patients with implantable cardioverter defibrillators: implications for tachycardia discrimination by dual chamber sensing

Incorporation of atrial electrograms in the tachycardia detection algorithm may improve tachyarrhythmia discrimination by ICDs but retrograde ventriculoatrial (VA) conduction over the AV node during ventricular tachyarrhythmia may be problematic. The present study analyzed VA conduction characteristics in 66 ICD patients who had evaluation of the VA conduction system by electrophysiological studies before implant. VA conduction was demonstrated in patients during ventricular decremental stimulation. Forty patients had inducible sustained monomorphic VT. The minimum cycle length maintaining 1:1 VA conduction during ventricular stimulation was longer than the cycle of VT in every patient (496 +/- 100 msec vs 320 +/- 81 msec; P < 0.01). Occasional VA conduction during VT was observed in five patients and one patient had 2:1 VA conduction during induced VT. No patient had 1:1 VA conduction during VT. We conclude that brisk VA conduction is uncommon and 1:1 VA conduction during VT is rare ICD recipients. VA conduction is unlikely to complicate the incorporation of atrial electrograms into tachyarrhythmia detection algorithms.

Intraoperative mapping is not necessary for VT surgery

Surgical ablation of ventricular tachycardia is generally guided by the results of pre- and intraoperative cardiac mapping. However, in certain situations intraoperative cardiac mapping may not be possible and, therefore, surgery has to be based on information obtained preoperatively. This raises the question whether intraoperative mapping is necessary for the success of this approach. We describe our experience with encircling endocardial cryoablation for ischemic VT and examine the contribution of intraoperative mapping for this procedure. Thirty-three patients with inducible VT refractory to medical therapy and a well defined anatomic scar were considered for surgery. All patients underwent baseline electrophysiology study and intraoperative mapping was attempted during normothermic cardiopulmonary bypass. In 14 patients, VT was inducible intraoperatively (Group 1) and surgical ablation was guided by this information, whereas in 19 patients, VT could not be mapped for various reasons (Group 2). Reasons for failure to obtain intraoperative map included noninducibility (3), nonsustained VT (8), polymorphic VT (4), VF (3), and incessant VT with hemodynamic collapse and cardiac arrest (1). The two groups did not differ with respect to age, location of myocardial infarction, or preoperative left ventricular ejection fraction. The operative procedures were similar in the two groups with respect to aortic cross clamp time, cardiopulmonary bypass time, number of cryoablation lesions, concomitant revascularization, aneurysmectomy, and ICD implantation. Encircling endocardial cryoablation was performed in 32 patients and one patient underwent partial right ventricular free wall disconnection (RV infarct). Thirteen patients underwent concomitant coronary artery bypass grafting (5 in Group 1 and 8 in group 2). One patient had prophylactic ICD patches (Group 1).(ABSTRACT TRUNCATED AT 250 WORDS)

Encircling endocardial cryoablation for ventricular tachycardia after myocardial infarction: experience with 33 patients

Encircling endocardial cryoablation, consisting of circumferential cryoablation of the infarct scar, can be curative in selected patients with ventricular tachycardia (VT). We describe our experience with and long-term outcome in 33 patients undergoing this procedure. The interval between myocardial infarction and the onset of tachycardia varied from 2 weeks to 22 years (mean 38 +/- 63 months and median 3 months). All patients had a left ventricular aneurysm (anterior in 20, posterior in 12, and lateral in 1) and significant coronary artery disease. Fourteen patients had clinical evidence of heart failure preoperatively. Twenty-eight patients had sustained monomorphic VT (incessant in 3); 3 had polymorphic or nonsustained tachycardia; 2 had primary ventricular fibrillation; and 1 had associated Wolff-Parkinson-White syndrome. Surgery was undertaken after failed drug therapy and consideration of left ventricular anatomy and function. At surgery, 32 patients had encircling endocardial cryoablation, and 1 patient had partial right ventricular free-wall disconnection (right ventricular infarct). Thirteen patients underwent concomitant coronary artery bypass grafting. An implantable cardioverter defibrillator (ICD) was implanted in 2 patients and prophylactic ICD patches in 1. One patient died postoperatively; 3 had recurrent VT perioperatively; 1 was treated with amiodarone; and 2 had ICD implantation. During long-term follow-up (mean 5 years), all patients who were free of tachycardia at discharge remained alive and free of arrhythmias or syncope. The patient receiving amiodarone sustained a cardiac arrest subsequently and received an ICD implant. One patient with an ICD continued to receive appropriate shocks frequently and died 2 years after surgery. Nine patients had congestive heart failure postoperatively.(ABSTRACT TRUNCATED AT 250 WORDS)

The value of electrophysiologic testing in patients resuscitated from documented ventricular fibrillation

INTRODUCTION

Electrophysiologic testing is performed in patients resuscitated from ventricular fibrillation (VF) on the assumption that sustained monomorphic ventricular tachycardia (VT) may be a precursor to VF, with the former amenable to assessment by serial drug testing.

METHODS AND RESULTS

We assessed the usefulness of this strategy by analyzing clinical and electrophysiologic data of 42 survivors (29 men and 13 women; mean age 54 +/- 14 years) of VF without a reversible cause. All patients had VF documented on ECG and required defibrillation. Underlying heart diseases included coronary disease in 28, dilated cardiomyopathy in 3, arrhythmogenic right ventricular dysplasia in 1, and no apparent structural heart disease in 10 patients. Only 2 (4.7%) patients had a prior history of documented VT. The electrophysiologic study was performed 7 to 30 days after VF. Programmed stimulation at the right ventricular apex using at least two drive cycle lengths and up to three extrastimuli induced sustained monomorphic VT in 4 (9.5%), sustained polymorphic VT in 3 (7.1%), nonsustained monomorphic VT in 1 (2.3%), nonsustained polymorphic VT in 5 (11.9%), and VF in 13 (30.9%) patients. Two patients with documented prior VT and coronary disease had sustained VT induced during the electrophysiologic study. On the other hand, sustained monomorphic VT was induced in 53 of the 59 (90%) patients (45 men and 14 women; mean age 57 +/- 16 years) with clinically documented VT concurrently studied using the same stimulation protocol.

CONCLUSION

We conclude that reproducible induction of sustained monomorphic VT in survivors of documented VF is uncommon. It may be more cost effective to proceed directly to treatment with implantable cardioverter defibrillators in these patients.

Complications of radiofrequency catheter ablation: a review

Radiofrequency catheter ablation has revolutionized the management of patients with supraventricular tachycardias. Although initial reports were very favourable, it is becoming apparent that radiofrequency catheter ablation may lead to some potentially serious complications. Complication rate for accessory pathway ablation ranges from 1.8 to 4% and the risk of atrioventricular (AV) block for 'AV nodal modification' ranges from 1.3 to 8%. It is likely that complications are underreported and the true incidence may be higher. Some of these complications are probably related to operator experience or the volume of ablations performed at the centre, but other complications, such as systemic embolism, may be sporadic and unrelated to experience or volume. Although radiofrequency catheter ablation has emerged as an excellent therapeutic tool, the potential complications and limitations should be recognized.

Fatigue phenomenon in accessory pathways

Fatigue phenomenon is transient failure of conduction following a period of repetitive excitation. Fatigue in accessory pathways is uncommon, and its electrophysiologic characteristics and clinical implications are unknown. Among the 215 patients who underwent electrophysiology studies from July 1992 to December 1993, 4 (2%) were found to exhibit fatigue over accessory pathways. The accessory pathway was posteroseptal in three patients and right free wall in one patient. The mean anterograde effective refractory period of the accessory pathway was 295 +/- 26 msec (range 270 to 330, basic drive cycle length 600 msec). Three patients had neither retrograde accessory pathway conduction nor inducible tachycardia even with infusion of isoproterenol. The fatigue phenomenon was observed after both atrial and ventricular stimulation in three patients and only after ventricular stimulation in one patient. Fatigue was dependent on duration more than rate of stimulation. We conclude that pathways exhibiting fatigue have a low margin of safety for conduction and are unlikely to be clinically problematic.