Reasons for prolonged or failed attempts at radiofrequency catheter ablation of accessory pathways.

OBJECTIVES: The purpose of this study was to categorize the reasons for a prolonged or failed procedure in a series of patients undergoing catheter ablation of an accessory pathway. BACKGROUND: Radiofrequency ablation of accessory pathways at times requires a lengthy procedure or a second ablation session, or both, and not prior studies have systematically investigated the reasons for this. METHODS: In a consecutive series of 619 patients undergoing catheter ablation of an accessory pathway, the mean ablation time +/- SD was 68 +/- 64 min. The subjects of this study were 14 patients who had an ablation time >2 SD greater than the mean (>196 min) and 51 patients who required a second ablation session for a successful outcome. The accessory pathway in the 65 patients in this study was located in the right free wall in 19 patients (29%), septum in 14 (22%) and left free wall in 32 (49%). RESULTS: The primary reasons for a lengthy or failed ablation attempt were 1) inability to position the ablation catheter at the effective target site (16 patients, 25%); 2) instability of the ablation catheter or inadequate tissue contact at the target site, or both (15 patients, 23%); 3) mapping error due to an oblique course of the accessory pathway (7 patients, 11%); 4) failure to recognize a posteroseptal accessory pathway as being left-sided instead of right-sided (4 patients, 6%); 5) other errors in accessory pathway localization (6 patients, 9%); 6) epicardial location of the accessory pathway (5 patients, 8%); 7) recurrent atrial fibrillation (2 patients, 3%); 8) occurrence of a complication (2 patients, 3%); 9) unusual right-sided accessory pathway that inserted in the anterior right ventricle, 2 cm away from the lateral tricuspid annulus (1 patient, 1.5%); and 10) unexplained factors (7 patients, 11%). The most common effective strategies employed to achieve a successful outcome in these patients were 1) substitution of a more experienced operator; 2) use of ablation catheters of varying configurations; 3) switching from a retrograde aortic to a trans-septal approach; 4) switching from an inferior to a superior vena caval approach; 5) use of a 60-cm guiding sheath; 6) detailed mapping of the atrial or ventricular insertion of the accessory pathway; and 7) searching within the coronary sinus for a presumed accessory pathway potential. CONCLUSIONS: A lengthy or failed attempt at catheter ablation of an accessory pathway may be due to a variety of reasons, the most common of which are problems related to some aspect of catheter manipulation and errors in accessory pathway localization. Knowledge of the most common reasons for a lengthy or ineffective procedure may facilitate successful outcome of accessory pathway ablation.

Response to pacing at sites of isolated diastolic potentials during ventricular tachycardia in patients with previous myocardial infarction.

OBJECTIVES: The goal of this study was to determine whether isolated diastolic potentials (IDPs) recorded during ventricular tachycardia (VT) are generated in zones of slow conduction and whether the arcs of block that bound these zones of slow conduction are functional or anatomic in nature. BACKGROUND: No previous studies have systematically investigated the response to pacing during VT and sinus rhythm at sites where IDPs are recorded. METHODS: The study included 11 patients with a previous infarction who underwent radiofrequency catheter ablation of 15 hemodynamically stable, sustained VTs and in whom an IDP that could not be dissociated from the VT was detected during mapping. RESULTS: Pacing during VT at the site where the IDP was recorded resulted in concealed entrainment in each of the 15 VTs. In 10 of the 15 VTs, an IDP was present during sinus rhythm at the same site at which a diastolic potential was recorded during VT. In nine VTs, the isolated potential occurred early in diastole; in these cases, the QRS configuration during pacing in the setting of sinus rhythm was different from that during VT. In six VTs, the isolated potential occurred later in diastole, and in these cases, the QRS configuration during pacing in the setting of sinus rhythm was the same as that during VT. CONCLUSIONS: Isolated diastolic potentials may often be generated in an area of slow conduction bounded by arcs of block that are anatomically determined and present during sinus rhythm.

2:1 atrioventricular block during atrioventricular node reentrant tachycardia.

OBJECTIVES: The purpose of this study was to determine the incidence and to clarify the mechanism of 2:1 atrioventricular (AV) block during AV node reentrant tachycardia induced in the electrophysiology laboratory. BACKGROUND: In patients with 2:1 AV block during AV node reentrant tachycardia, the absence of a His bundle potential in the blocked beats has been considered evidence of intranodal, lower common pathway block. METHODS: In consecutive patients with AV node reentrant tachycardia, the incidence of 2:1 AV block and the response to atropine and a single ventricular extrastimulus was observed. RESULTS: Persistent 2:1 AV block occurred in 13 of 139 patients with AV node reentrant tachycardia. A His bundle deflection was present in the blocked beats in eight patients and absent in five. Patients with 2:1 AV block had a shorter tachycardia cycle length than did patients without such block (mean +/- SD 312 +/- 32 vs. 353 +/- 55 ms, p < 0.01). Atropine did not alter the 2:1 block in any patient. In every patient, a single ventricular extrastimulus introduced during the tachycardia converted the 2:1 block to 1:1 conduction. CONCLUSIONS: The incidence of induced 2:1 AV block during AV node reentrant tachycardia is approximately 10%. The lack of a response to atropine and the consistent conversion of 2:1 block to 1:1 conduction by a ventricular extrastimulus indicate that, regardless of the presence or absence of a His bundle potential in blocked beats, 2:1 block during AV node reentrant tachycardia is due to functional infranodal block.

Long-term follow-up after radiofrequency modification of the atrioventricular node in patients with atrial fibrillation.

OBJECTIVES: The purpose of this study was to describe the long-term follow-up results in 62 patients with atrial fibrillation and an uncontrolled ventricular rate, who underwent radiofrequency modification of the atrioventricular (AV) node. BACKGROUND: Previous studies in small numbers of patients have suggested that radiofrequency modification may be effective in controlling the ventricular rate in patients with atrial fibrillation, but long-term follow-up data have been lacking. METHODS: The subjects of this study were 62 consecutive patients (mean age +/- SD 65 +/- 14 years; 43 with structural heart disease) who underwent an attempt at radiofrequency modification of the AV node because of symptomatic, drug-refractory atrial fibrillation with an uncontrolled ventricular rate. The atrial fibrillation was chronic in 46 patients and paroxysmal in 16. Radiofrequency energy was applied to the posteroseptal or mid-septal right atrium to lower the ventricular rate in atrial fibrillation to 120 to 130 beats/min during an infusion of 4 micrograms/min of isoproterenol. RESULTS: Short-term control of the ventricular rate was successfully achieved without the induction of pathologic AV block in 50 (81%) of 62 patients. Inadvertent high degree AV block occurred in 10 (16%) of 62 patients, with the AV block occurring at the time of the procedure in 6 patients and 36 to 72 h after the procedure in 4. During 19 +/- 8 months of follow-up (range 4 to 33), 5 (10%) of 50 patients had a symptomatic recurrence of an uncontrolled rate during atrial fibrillation. Overall, adequate rate control at rest and during exertion, without pathologic AV block, was achieved long term in 45 (73%) of 62 patients. Among 37 patients with a successful outcome, left ventricular ejection fraction increased from (mean +/- SD) 0.44 +/- 0.14 to 0.51 +/- 0.10 one year later (p < 0.001). Complications other than AV block included polymorphic ventricular tachycardia 10 to 24 h after the procedure in two patients who had a predisposing factor for ventricular tachycardia and sudden death 1 to 5 months after the procedure in two patients with idiopathic dilated cardiomyopathy, one of whom had a pacemaker for AV block. CONCLUSIONS: In approximately 70% of properly selected patients with atrial fibrillation and an uncontrolled ventricular rate, radiofrequency modification of the AV node results in excellent long-term control of the ventricular rate at rest and during exertion.

Slow pathway ablation in patients with documented but noninducible paroxysmal supraventricular tachycardia.

OBJECTIVES: The purpose of this study was to assess the clinical efficacy of radiofrequency ablation of the slow pathway in patients with documented but noninducible paroxysmal supraventricular tachycardia (PSVT) who have evidence of dual atrioventricular (AV) node pathways. BACKGROUND: Patients with a documented history of PSVT at times do not have inducible PSVT in the electrophysiology laboratory. Because dual AV node pathways serve as the substrate for AV node reentrant tachycardia (AVNRT), ablation of the slow pathway potentially may be useful in these patients. METHODS: The subjects in this prospective study were seven consecutive patients who underwent an electrophysiologic procedure because of documented PSVT and were found to have dual AV node physiology or inducible single AV node echo beats, but no inducible PSVT despite the administration of isoproterenol and atropine. Their mean (+/- SD) age was 33 +/- 13 years, and they had been symptomatic for 12 +/- 12 years. The frequency of the episodes of PSVT ranged from > or = 1/day to 1/month. The rate of the documented episodes ranged from 170 to 260 beats/min, and discrete P waves were not apparent. Slow pathway ablation was performed with 9 +/- 4 applications of radiofrequency energy using a combined anatomic and electrogram mapping approach. RESULTS: All evidence of dual AV node pathways was eliminated in six patients, and dual AV node physiology remained present in one patient. During a mean follow-up period of 15 +/- 10 months (range 8 to 27), no patient had a recurrence of symptomatic tachycardia (success rate 95% confidence interval 65% to 100%). CONCLUSIONS: Slow pathway ablation may be clinically useful in patients with documented but noinducible PSVT who have evidence of dual AV node pathways.

Randomized comparison of slow pathway modification within the posteroseptal versus the midseptal area in patients with atrioventricular nodal reentrant tachycardia.

A total of 332 local electrogram recordings including 62 successful and 270 unsuccessful sites were analyzed. Univariate analysis revealed that there was a longer duration and more peaks of the atrial electrogram with a lower atrioventricular ratio and a higher incidence and shorter onset time of junctional ectopy during energy delivery at successful than at unsuccessful target sites.

Septal Q waves in surface electrocardiographic lead V6 exclude minimal ventricular preexcitation.

Electrocardiograms of 37 consecutive patients with minimal preexcitation (i.e., PR >120 ms, QRS <120 ms) were compared before and after ablation with electrocardiograms of 37 age-matched patients with atrioventricular nodal reentrant tachycardia. The presence of a septal Q wave could be used to exclude minimal preexcitation with a high degree of reliability in both patients and controls before and after radiofrequency ablation.

Effect of an irregular ventricular rhythm on cardiac output.

Impairment of cardiac function in atrial fibrillation has been attributed to loss of atrial contraction and to a rapid ventricular rate. The results of this study suggest that irregularity of the ventricular rhythm, independent of the ventricular rate, may also contribute to impairment of cardiac function during atrial fibrillation.

QT dispersion in nonsustained ventricular tachycardia and coronary artery disease.

This study examines the relation between QT dispersion and the inducibility of ventricular tachycardia (VT) in 35 consecutive patients with coronary artery disease who underwent electrophysiologic testing for evaluation of nonsustained VT. The mean age of the patients was 66 +/- 9 years (+/- SD) and the mean left ventricular ejection fraction was 0.36 +/- 0.14. In 6 patients in whom sustained, monomorphic VT was inducible by programmed ventricular stimulation, QT dispersion was significantly greater than in the 29 patients in whom VT was not inducible (126 +/- 35 vs 67 +/- 25 ms, p < 0.001). All patients who had a QT dispersion > 120 ms had inducible sustained monomorphic VT, and no patient who had a QT dispersion < 90 ms had inducible VT. The patients who had inducible VT dis not differ significantly from those who did not with regard to age, gender, ejection fraction, RR interval, or mean QT. In conclusion, in patients with coronary artery disease who have nonsustained VT, inducibility of monomorphic VT is associated with an increase in QT dispersion. QT dispersion may be helpful in predicting which patients with nonsustained VT are and are not likely to have inducible VT by programmed stimulation.

Local calcification as a determinant of the outcome of excimer laser coronary angioplasty: an in vitro study.

BACKGROUND: Calcification influences the outcome of various angioplasty techniques in the treatment of coronary artery disease. During angioscopic in vitro studies, we observed that dissections and perforations not caused by vessel bending frequently occurred at the boundary areas of plaque and adjacent vessel wall. This study investigated whether this is related to the distribution of calcific deposits. METHODS: Postmortem excimer laser coronary angioplasty (308-nm XeCl) was performed in 51 stenotic coronary arteries. Twenty-three segments were further examined; these consisted of 11 perforations, six dissections, three segments with no ablative effect after the application of 20,000 laser impulses, and three successfully passed stenoses without complications. X-ray diffraction analysis and scanning electron microscopy were performed to detect calcium deposits and their spatial relationship to perforations and dissections. RESULTS: X-ray diffractions analysis detected calcifications in 21 of 23 specimens. Postmortem angiography revealed calcifications only on 11 of 23 segments. Three of 11 perforations were located at the plaque border, as were three of six dissections. In all six complications at the plaque border, x-ray diffraction analysis revealed that the plaque border was identical with a border of calcium deposits. Eight of 11 perforations and three of six dissections could be explained by axis divergence between the laser catheter and the vessel orientation. CONCLUSIONS: Contributing factors for perforations and dissections during excimer laser coronary angioplasty are axis divergence and the distribution of plaque calcification. More sensitive methods are needed to detect local vessel wall calcium in vivo.

A randomized comparison of fixed power and temperature monitoring during slow pathway ablation in patients with atrioventricular nodal reentrant tachycardia.

Temperature monitoring may be helpful for ablation of accessory pathways, however its role in ablation of atrioventricular nodal reentrant tachycardia (AVNRT) using the slow pathway approach is unclear. Therefore, the purpose of this study was to prospectively compare slow pathway ablation for AVNRT using fixed power or temperature monitoring. The study included 120 patients undergoing ablation for AVNRT. Patients were randomly assigned to receive either fixed power at 32 watts, or to temperature monitoring with a target temperature of 60 degrees C. The primary success rate was 72% in the fixed power group and 95% in the temperature monitoring group (p = 0.001). The ablation procedure duration (35 +/- 29 min vs 35 +/- 30 min; p = 0.9), fluoroscopic time (32 +/- 17 vs 35 +/- 19 min; p = 0.4), mean number of applications (10.2 +/- 8.1 vs 8.4 +/- 7.9; p = 0.2), and coagulum formation per application (0.2% vs 0.5%; p = 0.6) were statistically similar in the fixed power and temperature monitoring groups, respectively. The mean temperature (47.3 +/- 4.8 degrees C vs 48.6 +/- 3.8 degrees C; p < 0.01), and the temperature associated with junctional ectopy (48.2 +/- 3.8 degrees C vs 49.3 +/- 3.6 degrees C, p < 0.01) were less for the fixed power than the temperature monitoring group. In the temperature monitoring group, only 31% of applications achieved an electrode temperature of 60 degrees C. During follow up of 6.6 +/- 3.6 months there were two recurrences in the fixed power group and one in the temperature monitoring group (p = 1.0). In summary, power titration directed by temperature monitoring was associated with an improved primary procedural success rate. Applications of energy were associated with a temperature of approximately 50 degrees C with both techniques, suggesting that there is a low efficiency of heating in the posterior septum.

Outpatient radiofrequency catheter ablation.

Outpatient radiofrequency catheter ablation has been shown to be safe and cost effective in the treatment of supraventricular tachycardias due to atrioventricular nodal reentrant tachycardia and atrioventricular reentry tachycardia. Complications secondary to vascular access are similar to those during outpatient cardiac catheterization procedures. Specific complications due to catheter manipulation and radiofrequency ablation include among others cardiac tamponade, AV block and proarrhythmia. Proper patient selection can help to prevent specific complications in outpatient ablations. Patients probably not suitable for outpatient procedures include the elderly as well as comorbid patients. Not all ablation procedures are suitable for the outpatient setting. Ablation procedures with an increased risk of AV block or proarrhythmia should not be performed on an outpatient basis. In order to effectively perform outpatient procedures a back up support with specially trained personnel is helpful. Radiofrequency ablations require considerable experience, therefore ablation procedures int he outpatient setting should be restricted to operators with adequate experience.

Ablation of atypical atrial flutter guided by the use of concealed entrainment in patients without prior cardiac surgery.

INTRODUCTION: Mapping techniques have not been systematically evaluated with respect to atypical atrial flutter (AF) not involving the inferior vena cava isthmus. The purpose of this study was to assess prospectively the use of concealed entrainment (CE) in mapping of AF and to assess the clinical benefit of ablation of clinically relevant atypical AF. METHODS AND RESULTS: In seven consecutive patients without prior cardiac surgery presenting with atypical AF, mapping was performed in the right and, if necessary, left atrium. At sites with CE, radiofrequency energy was delivered. In a posthoc analysis, the endocardial activation time, stimulus-flutter wave (F) interval, presence of split potentials and diastolic potentials, and postpacing interval were assessed, and effective sites were compared to ineffective sites. A total of 22 forms of atypical AF either could be induced or were present at the time of the study. Eleven of the 13 targeted atypical AFs (85%) were successfully ablated. The positive predictive value of CE increased from 45% to 75% in the presence of matching electrogram-F and stimulus-F intervals or if flutter terminated during entrainment pacing, and to 88% in the presence of split atrial electrograms or diastolic potentials. During short-term clinical follow-up, none of the patients had recurrence of the ablated AF. However, the majority of patients required either medication for atrial fibrillation or repeated interventions for new forms of AF. CONCLUSION: Mapping and ablation of atypical AF is feasible if sites with CE can be identified. However, the clinical benefit of successful ablations in patients with atypical flutter appears to be limited.

Efficacy and safety of transvenous atrial cardioversion in patients with mitral valve disease and long-standing atrial fibrillation.

BACKGROUND: Transvenous internal cardioversion (ICV) of atrial fibrillation (AF) may be successful after unsuccessful external CV. However, the safety and efficacy of ICV in patients with significant mitral valve disease and AF of long duration have not been evaluated prospectively. METHODS: This study included 22 consecutive patients (mean age = 59 +/- 14 years, 12 women) with mitral regurgitation grade = II (n = 14) or after mitral valve replacement (n = 8), who underwent ICV with 3/3 ms biphasic shocks delivered via two defibrillation catheters placed in the right atrium and the coronary sinus, respectively. The mean left atrial diameter was 53 +/- 7 mm (range 45-68), and AF had been diagnosed for a median of 24 months. All patients received oral amiodarone pretreatment followed by a maintenance dose of 200 mg/day. RESULTS: Sinus rhythm (SR) was restored by ICV in 15/20 patients (75%), and returned spontaneously in two patients during amiodarone pretreatment. The mean threshold for ICV was 6.2 +/- 3.5 J. Sinus node disease was present in one patient after ICV, and two patients developed amiodarone-induced hyperthyroidism. During a follow-up of 11 +/- 5 months, 8 patients had recurrent AF. The remaining 11 patients who were successfully cardioverted remained in stable SR. CONCLUSION: SR can be safely and successfully restored by ICV in patients with MVD and long-standing AF. During intermediate-term follow-up, a significant proportion of patients remained in SR with oral amiodarone therapy.

Clinical value of the postpacing interval for mapping of ventricular tachycardia in patients with prior myocardial infarction.

INTRODUCTION: The postpacing interval (PPI) has been used to discriminate bystander sites from critical sites within a ventricular tachycardia (VT) reentry circuit, with a PPI that is similar to the VT cycle length (CL) being indicative of a site within the reentry circuit. The purpose of this study was to assess the clinical value of the PPI for identifying effective target sites for ablation of VT at sites of concealed entrainment in patients with prior myocardial infarction. METHODS AND RESULTS: In 24 patients with coronary artery disease and a past history of myocardial infarction, 36 VTs with a mean CL of 483+/-80 msec (+/- SD) were mapped and targeted for radiofrequency (RF) ablation. The only criterion used to select target sites for ablation was concealed entrainment. In a post hoc analysis, the PPI was measured at 47 ineffective and 26 effective ablation sites. The mean PPI-VTCL difference at the 26 effective sites (114+/-137 msec) did not differ significantly from the mean at the 47 ineffective sites (177+/-161 msec; P = 0.1). The sensitivity of a PPI-VTCL difference < or = 30 msec for identifying an effective ablation site was 46%, the specificity 64%, the positive predictive value 41%, and the negative predictive value 68%. CONCLUSION: The PPI-VTCL difference is not useful for discriminating between sites of concealed entrainment that are within or outside of a VT reentry circuit in patients with prior infarction. Therefore, in patients with prior infarction, the PPI is not clinically useful for identifying sites of concealed entrainment at which RF ablation should or should not be attempted.

Location of the lower turnaround point in typical AV nodal reentrant tachycardia: a quantitative model.

INTRODUCTION: Recent observations suggest that the circuit of AV nodal reentrant tachycardia (AVNRT) may extend down to the His bundle. The purpose of this study was to develop a quantitative model indicating the location of the lower turnaround point in AVNRT. METHODS AND RESULTS: Slow pathway modification was performed in 70 patients with typical AVNRT. During sinus rhythm, ventricular pacing was performed with the AVNRT cycle length. During AVNRT, the HinitAinit interval was measured from initial His to the initial atrial deflection recorded in the His-bundle lead. During ventricular pacing, the HendAinit interval was measured from end of the His to the beginning of the atrial deflection. It was hypothesized that x reflects conduction time from the lower turnaround point to Ainit, whereas y reflects conduction time from the lower turnaround point to Hinit. Anterograde conduction during AVNRT and retrograde conduction during ventricular pacing were assumed to be identical if there was 1:1 retrograde conduction at the AVNRT cycle length. The following formulas describe the relation of the measured parameters: x - y = HinitAinit; and x + y = HendAinit. Resolving both formulas yields the unknown x and y: y = (HendAinit - HinitAinit)/2, x = (HendAinit + HinitAinit)/2. These criteria were present in 52 of 70 patients. The mean cycle length of AVNRT was 355 +/- 42 msec, mean HinitAinit was 54 +/- 27 msec, and mean HendAinit was 60 +/- 29 msec. Accordingly, in 20 of 52 patients, the lower turnaround point was located within the His bundle (y = -15.4 +/- 16.1 msec), in 3 of 52 it was in the nodal-His junctional area (y = 0), and in 29 of 52 it was above the His bundle (y = +12.7 +/- 10.3 msec). The HinitAinit interval was significantly longer (66 +/- 32 msec vs 47 +/- 20 msec; P = 0.02) and the HendAinit interval was significantly shorter (45 +/- 30 msec vs 69 +/- 24 msec; P = 0.004) when the first group was compared with the others. CONCLUSION: In about 1 of 3 of patients with typical AVNRT, the lower turnaround point of the circuit is within the His bundle; in more than half of the patients it is above the His bundle. These data do not support the concept that all AVNRTs have an intranodal circuit, but are in accordance with the finding of longitudinal dissociation of the His bundle.

Ventricular rate during atrial fibrillation before and after slow-pathway ablation. Effects of autonomic blockade and beta-adrenergic stimulation.

BACKGROUND: Radiofrequency catheter modification of AV conduction can be used to control the ventricular rate during atrial fibrillation both in the baseline state and during exercise. Slow-pathway ablation has been suggested to be the mechanism for this response. The purpose of this study was to determine the effect of slow-pathway ablation on the ventricular rate in atrial fibrillation during autonomic blockade and sympathetic stimulation in patients with AV nodal reentrant tachycardia (AVNRT). METHODS AND RESULTS: Thirty-five patients undergoing slow-pathway radiofrequency ablation for AVNRT were assigned to autonomic blockade (0.2 mg/kg propranolol and 0.04 mg/kg atropine; n = 14) or isoproterenol (2 micrograms/min; n = 21). Atrial fibrillation was induced before and after slow-pathway radiofrequency ablation. During autonomic blockade, the mean ventricular cycle length (448 +/- 34 versus 525 +/- 103 ms, P < .01) and maximum ventricular cycle length (640 +/- 105 versus 798 +/- 226 ms, P = .04) were prolonged after ablation, whereas the minimum ventricular cycle length did not change significantly (361 +/- 42 versus 403 +/- 83 ms, P = .05). During isoproterenol infusion, the mean ventricular cycle length (375 +/- 52 versus 390 +/- 61 ms, P = .2), maximum ventricular cycle length (520 +/- 88 versus 537 +/- 106 ms, P = .3), and minimum ventricular cycle length (307 +/- 59 versus 298 +/- 33 ms, P = .4) did not change significantly after slow-pathway ablation. CONCLUSION: Slow-pathway ablation slows the ventricular rate during atrial fibrillation under conditions of autonomic blockade but not during sympathetic stimulation. Therefore, slow-pathway ablation alone cannot account for the clinical results obtained with radiofrequency modification of AV conduction in patients with atrial fibrillation.

Effect of atrial fibrillation on atrial refractoriness in humans.

BACKGROUND: The acute effect of atrial fibrillation (AF) on the atrial effective refractory period (ERP) in humans is unknown. METHODS AND RESULTS: In 20 patients without structural heart disease, the atrial ERP was measured before and after pacing-induced AF at drive cycle lengths of 350 and 500 ms. Immediately after spontaneous AF conversion, the post-AF ERP was measured. The pre-AF ERPs at 350 and 500 ms were 206 +/- 23 and 216 +/- 17 ms, respectively. The time to spontaneous conversion of AF was 7.3 +/- 1.9 minutes. The first post-AF ERPs at drive cycle lengths of 350 and 500 ms were 175 +/- 30 ms (P < .0001 versus pre-AF) and 191 +/- 30 ms (P < .0001 versus pre-AF), respectively. The post-AF ERP returned to the pre-AF ERP value after a mean of 8.4 +/- 0.3 minutes. In 15 patients, during the determination of the post-AF ERP, secondary episodes of AF lasting 1 +/- 1.5 minutes were reinduced 6 +/- 3 times per patient. There was a significant inverse logarithmic relationship between the time to reinduction of AF and the duration of secondary episodes of AF (P < .0001, r = 5). CONCLUSIONS: In humans, several minutes of induced AF is sufficient to shorten the ERP for up to approximately 8 minutes. The temporal recovery of the ERP is reflected in progressively shorter episodes of reinduced AF. These data imply that AF transiently shortens the atrial wavelength and suggest a mechanism by which AF may perpetuate itself.

Radiofrequency ablation of idiopathic left anterior fascicular tachycardia.

INTRODUCTION: A 45-year-old man with idiopathic ventricular tachycardia (VT) having a right bundle branch block configuration with right-axis deviation underwent an electrophysiologic test. METHODS AND RESULTS: Mapping demonstrated a site on the anterobasal wall of the left ventricle where there was an excellent pace map and an endocardial activation time of -20 msec, but radiofrequency catheter ablation at this site was unsuccessful. At a nearby site, a presumed Purkinje potential preceded the by 30 msec during VT and sinus rhythm, and catheter ablation was effective despite a poor pace map and an endocardial ventricular activation time of zero. CONCLUSION: Idiopathic VT with a right bundle branch configuration and right-axis deviation may originate in the area of the left anterior fascicle. A potential presumed to represent a Purkinje potential may be more helpful than endocardial ventricular activation mapping or pace mapping in guiding ablation of this type of VT.

Discrete systolic potentials during ventricular tachycardia in patients with prior myocardial infarction.

INTRODUCTION: Isolated diastolic potentials have been found to be helpful in identifying critical sites for ablation of ventricular tachycardia (VT) in patients with coronary artery disease. However, discrete potentials that occur during systole have not been previously described. The purpose of this study was to determine the significance of discrete systolic potentials during VT in patients with coronary artery disease. METHODS AND RESULTS: Twenty-seven patients with a mean age of 66 +/- 12 years ( +/- standard deviation) who had coronary artery disease underwent radiofrequency catheter ablation of 42 VTs that had a mean cycle length of 486 +/- 78 msec. The only criterion used to select target sites for ablation was concealed entrainment, which was present at 92 sites. Thirty-five of the 42 VTs (83%) were successfully ablated. A discrete systolic potential was recorded during 7 of the 42 VTs (17%). In all cases, the interval between the discrete systolic potential and the next QRS complex was equal to the stimulus-QRS interval during concealed entrainment. At all seven sites where a discrete systolic potential was recorded, delivery of radiofrequency energy resulted in successful ablation of the VT. CONCLUSION: Discrete systolic potentials may be present in patients with coronary artery disease in approximately 17% of VTs in which there is concealed entrainment. If the interval between the discrete systolic potential and the next QRS complex matches the stimulus-QRS interval during concealed entrainment, delivery of radiofrequency energy is likely to result in successful ablation of the VT.