Life-threatening ventricular arrhythmias due to transient or correctable causes: high risk for death in follow-up.

OBJECTIVES: This study evaluated the prognosis of patients resuscitated from ventricular tachycardia (VT) or ventricular fibrillation (VF) with a transient or correctable cause suspected as the cause of the VT/VF. BACKGROUND: Patients resuscitated from VT/VF in whom a transient or correctable cause has been identified are thought to be at low risk for recurrence and often receive no primary treatment for their arrhythmias. METHODS: In the Antiarrhythmics Versus Implantable Defibrillators (AVID) trial, patients with a potentially transient or correctable cause of VT/VF were not eligible for randomization. The mortality of these patients was compared with the mortality of patients with a known high risk of recurrence of VT/VF in the AVID registry. RESULTS: Compared with patients having high risk VT/VF, those with a transient or correctable cause for their presenting VT/VF were younger and had a higher left ventricular ejection fraction. These patients were more often treated with revascularization as the primary therapy, more commonly received a beta-blocker, less often required therapy for congestive heart failure and less commonly received either an antiarrhythmic drug or an implantable cardioverter defibrillator. Nevertheless, subsequent mortality of patients with a transient or correctable cause of VT/VF was no different or perhaps even worse than that of the primary VT/VF population. CONCLUSIONS: Patients identified with a transient or correctable cause for their VT/VF remain at high risk for death. Further research is needed to define truly reversible causes of VT/VF. Meanwhile, these patients may require more aggressive evaluation, treatment and follow-up than is currently practiced.

Reversing the direction of paced ventricular and atrial wavefronts reveals an oblique course in accessory AV pathways and improves localization for catheter ablation.

BACKGROUND: The purpose of this study was to determine how often accessory atrioventricular (AV) pathways (AP) cross the AV groove obliquely. With an oblique course, the local ventriculoatrial (VA) interval at the site of earliest atrial activation (local-VA) and the local-AV interval at the site of earliest ventricular activation (local-AV) should vary by reversing the direction of the paced ventricular and atrial wavefronts, respectively. METHODS AND RESULTS: One hundred fourteen patients with a single AP were studied. Two ventricular and two atrial pacing sites on opposite sides of the AP were selected to reverse the direction of the ventricular and atrial wavefronts along the annulus. Reversing the ventricular wavefront increased local-VA by >/=15 ms in 91 of 106 (91%) patients. With the shorter local-VA, the ventricular potential overlapped the atrial potential along a 17.2+/-8.5-mm length of the annulus. No overlap occurred with the opposite wavefront. Reversing the atrial wavefront increased local-AV by >/=15 ms in 32 of 44 (73%) patients. With the shorter local-AV, the atrial potential overlapped the ventricular potential along an 11.9+/-8.9-mm length of the annulus. No overlap occurred with the opposite wavefront. Mapping during longer local-VA or local-AV identified an AP potential in 102 of 114 (89%) patients. Catheter ablation eliminated AP conduction in all 111 patients attempted (median, 1 radiofrequency application in 99 patients with an AP potential versus 4.5 applications without an AP potential). CONCLUSIONS: Reversing the direction of the paced ventricular or atrial wavefront reveals an oblique course in most APs and facilitates localization of the AP potential for catheter ablation.

Unexpectedly high defibrillation thresholds in an active can implantable cardioverter defibrillator system.

This case report describes a patient undergoing defibrillator generator replacement in whom the defibrillation thresholds were significantly higher with a can-active system than with a non-active can system.

Electrical storm presages nonsudden death: the antiarrhythmics versus implantable defibrillators (AVID) trial.

BACKGROUND: Electrical storm, multiple temporally related episodes of ventricular tachycardia (VT) or ventricular fibrillation (VF), is a frequent problem among recipients of implantable cardioverter defibrillators (ICDs). However, insufficient data exist regarding its prognostic significance. METHODS AND RESULTS: This analysis includes 457 patients who received an ICD in the Antiarrhythmics Versus Implantable Defibrillators (AVID) trial and who were followed for 31 +/- 13 months. Electrical storm was defined as > or = 3 separate episodes of VT/VF within 24 hours. Characteristics and survival of patients surviving electrical storm (n = 90), those with VT/VF unrelated to electrical storm (n = 184), and the remaining patients (n = 183) were compared. The 3 groups differed in terms of ejection fraction, index arrhythmia, revascularization status, and baseline medication use. Survival was evaluated using time-dependent Cox modeling. Electrical storm occurred 9.2 +/- 11.5 months after ICD implantation, and most episodes (86%) were due to VT. Electrical storm was a significant risk factor for subsequent death, independent of ejection fraction and other prognostic variables (relative risk [RR], 2.4; 95% confidence interval [CI], 1.3 to 4.2; P = 0.003), but VT/VF unrelated to electrical storm was not (RR, 1.0; 95% CI, 0.6 to 1.7; P = 0.9). The risk of death was greatest 3 months after electrical storm (RR, 5.4; 95% Cl, 2.4 to 12.3; P = 0.0001) and diminished beyond this time (RR, 1.9; 95% CI, 1.0 to 3.6; P=0.04). CONCLUSIONS: Electrical storm is an important, independent marker for subsequent death among ICD recipients, particularly in the first 3 months after its occurrence. However, the development of VT/VF unrelated to electrical storm does not seem to be associated with an increased risk of subsequent death.

Transseptal left heart catheterization for cardiac ablation procedures.

UNLABELLED: Transseptal left heart catheterization has been performed as an alternative to the retrograde approach since 1958. However, this procedure can result in life-threatening complications, some of which may occur because of insufficient anatomical landmarks. Accordingly, we sought to assess the safety and efficacy of a new transseptal left heart catheterization technique designed for ablation procedures. Specifically, we examined whether electrode catheters could be used as anatomical landmarks, permitting identification of the aortic root and other critical structures. RESULTS: One hundred and eight consecutive patients underwent transseptal left heart catheterization under biplane fluoroscopy during catheter ablation. Electrode catheters positioned in the right atrial appendage, His bundle region, and coronary sinus were used as anatomical landmarks to guide the transseptal unit to the fossa ovalis. The angles of the right anterior and left anterior oblique projections were selected in each patient based on the orientation of the His bundle and coronary sinus catheters. Transseptal left heart catheterization was successfully performed in all patients without complications. In contrast to previous reports, the direction of the needle at the successful puncture site in the last 96 patients varied substantially: 2 o'clock in 13 patients (13 %); 3 o'clock in 43 patients (45 %); and 4 o'clock in 40 patients (42 %). CONCLUSION: The use of electrode catheters as anatomical landmarks and biplane fluoroscopy facilitates transseptal catheterization. This approach can be used safely during catheter ablation procedures.

Characterization of reentrant circuit in macroreentrant right atrial tachycardia after surgical repair of congenital heart disease: isolated channels between scars allow "focal" ablation.

BACKGROUND: The purpose of this study was to characterize the circuit of macroreentrant right atrial tachycardia (MacroAT) in patients after surgical repair of congenital heart disease (SR-CHD). METHODS AND RESULTS: Sixteen patients with atrial tachycardia (AT) after SR-CHD were studied (atrial septal defect in 6, tetralogy of Fallot in 4, and Fontan procedure in 6). Electroanatomic right atrial maps were obtained during 15 MacroATs in 13 patients, focal AT in 1 patient, and atrial pacing in 2 patients without stable AT. A large area of low bipolar voltage (/=2 scars forming narrow channels. Ablation within the channels eliminates MacroAT.

Development and validation of an ECG algorithm for identifying accessory pathway ablation site in Wolff-Parkinson-White syndrome.

INTRODUCTION: Delta wave morphology correlates with the site of ventricular insertion of accessory AV pathways. Because lesions due to radiofrequency (RF) current are small and well defined, it may allow precise localization of accessory pathways. The purpose of this study was to use RF catheter ablation to develop an ECG algorithm to predict accessory pathway location. METHODS AND RESULTS: An algorithm was developed by correlating a resting 12-lead ECG with the successful RF ablation site in 135 consecutive patients with a single, anterogradely conducting accessory pathway (Retrospective phase). This algorithm was subsequently tested prospectively in 121 consecutive patients (Prospective phase). The ECG findings included the initial 20 msec of the delta wave in leads I, II, aVF, and V1 [classified as positive (+), negative (-), or isoelectric (+/-)] and the ratio of R and S wave amplitudes in leads III and V1 (classified as R > or = S or R < S). When tested prospectively, the ECG algorithm accurately localized the accessory pathway to 1 of 10 sites around the tricuspid and mitral annuli or at subepicardial locations within the venous system of the heart. Overall sensitivity was 90% and specificity was 99%. The algorithm was particularly useful in correctly localizing anteroseptal (sensitivity 75%, specificity 99%), and mid-septal (sensitivity 100%, specificity 98%) accessory pathways as well as pathways requiring ablation from within ventricular venous branches or anomalies of the coronary sinus (sensitivity 100%, specificity 100%). CONCLUSION: A simple ECG algorithm identifies accessory pathway ablation site in Wolff-Parkinson-White syndrome. A truly negative delta wave in lead II predicts ablation within the coronary venous system.

Acute hemodynamic effects of intravenous ibutilide in patients with or without reduced left ventricular function.

Many antiarrhythmic agents have adverse hemodynamic effects which limit their use in patients with impaired ventricular function or during tachyarrhythmias. Ibutilide is an intravenous, selective class III antiarrhythmic agent that is effective for conversion of atrial fibrillation or flutter. This multicenter, randomized, placebo-controlled, dose-ranging study evaluated the effects of intravenous ibutilide on hemodynamic parameters during invasive monitoring in 47 patients with or without reduced left ventricular ejection fraction (LVEF) > 35% or < or = 35%. Patients received either placebo or ibutilide as a 10-minute loading and a 30-minute maintenance infusion using 1 of the following dosing regimens: placebo then placebo (n = 12); 0.01 then 0.002 mg/kg (n = 12); 0.02 then 0.004 mg/kg (n = 12); or 0.03 then 0.006 mg/kg (n = 11). Ibutilide significantly increased QT and QTc intervals in a dose-related manner with mean increases ranging from 51 to 99 ms, but did not alter the PR interval or QRS duration. During ibutilide infusion, a few small but statistically significant changes from baseline in several hemodynamic variables were present. However, the changes in cardiac output, pulmonary artery or capillary wedge pressures, blood pressure, or heart rate in patients receiving ibutilide were not significantly different from the changes in patients receiving placebo. Thus, ibutilide did not cause clinically important adverse hemodynamic effects, even in patients with depressed ventricular function. One patient developed 2 episodes of nonsustained torsades de pointes during ibutilide. These results demonstrate that with careful monitoring for proarrhythmia, ibutilide can be used safely from a hemodynamic standpoint in the acute treatment of arrhythmias, even in patients with reduced ventricular function.

Para-Hisian pacing. A new method for differentiating retrograde conduction over an accessory AV pathway from conduction over the AV node.

BACKGROUND: Differentiation between ventriculoatrial (VA) conduction over an accessory AV pathway (AP) and the AV node (AVN) may be difficult, especially in patients with a septal AP. METHODS AND RESULTS: A new pacing method, para-Hisian pacing, was tested in 149 patients with AP and 53 patients without AP who had AV nodal reentrant tachycardia (AVNRT). Ventricular pacing was performed adjacent to the His bundle and proximal right bundle branch (HB-RB), initially at high output to capture both RV and HB-RB. The output was then decreased to lose HB-RB capture. The change in timing and sequence of retrograde atrial activation between HB-RB capture and noncapture was examined. Loss of HB-RB capture without change in stimulus-atrial (S-A) interval or atrial activation sequence indicated exclusive retrograde AP conduction. An increase in S-A interval without change in His bundle-atrial interval or atrial activation sequence indicated exclusive retrograde AVN conduction. A change in atrial activation sequence indicated the presence of both retrograde AP and AVN conduction. Para-Hisian pacing correctly identified retrograde AP conduction in 132 of 147 AP patients, including all septal and right free wall APs. Retrograde AVN conduction masked AP conduction in 9 of 34 patients with a left free wall AP and 6 of 9 patients with the permanent form of junctional reciprocating tachycardia. Para-Hisian pacing correctly excluded AP conduction in all 53 patients with AVNRT. CONCLUSIONS: Para-Hisian pacing reliably identifies retrograde conduction over septal and right free wall APs, but AVN conduction may mask APs located far from the pacing site or with a long retrograde conduction time.

Role of the tricuspid annulus and the eustachian valve/ridge on atrial flutter. Relevance to catheter ablation of the septal isthmus and a new technique for rapid identification of ablation success.

BACKGROUND: Typical atrial flutter (AFL) results from right atrial reentry by propagation through an isthmus between the inferior vena cava (IVC) and tricuspid annulus (TA). We postulated that the eustachian valve and ridge (EVR) forms a line of conduction block between the IVC and coronary sinus (CS) ostium and forms a second isthmus (septal isthmus) between the TA and CS ostium. METHODS AND RESULTS: Endocardial mapping in 30 patients with AFL demonstrated atrial activation around the TA in the counter-clockwise direction (left anterior oblique projection). Double atrial potentials were recorded along the EVR in all patients during AFL. Pacing either side of the EVR during sinus rhythm also produced double potentials, which indicated fixed anatomic block across EVR. Entrainment pacing at the septal isthmus and multiple sites around the TA produced a delta return interval < or = 8 ms in 14 of 15 patients tested. Catheter ablation eliminated AFL in all patients by ablation of the septal isthmus in 26 patients and the posterior isthmus in 4. AFL recurred in 2 of 12 patients (mean follow-up, 33.9 +/- 16.3 months) in whom ablation success was defined by the inability to reinduce AFL, compared with none of 18 patients (mean follow-up, 10.3 +/- 8.3 months) in whom success required formation of a complete line of conduction block between the TA and the EVR, identified by CS pacing that produced atrial activation around the TA only in the counterclockwise direction and by pacing the posterior TA with only clockwise atrial activation. CONCLUSIONS: (1) The EVR forms a line of fixed conduction block between the IVC and the CS; (2) the EVR and the TA provide boundaries for the AFL reentrant circuit; and (3) verification of a complete line of block between the TA and the EVR is a more reliable criterion for long-term ablation success.

Comparison of in vivo tissue temperature profile and lesion geometry for radiofrequency ablation with a saline-irrigated electrode versus temperature control in a canine thigh muscle preparation.

BACKGROUND: It is thought that only a thin layer of tissue adjacent to the electrode is heated directly by electrical current (resistive heating) during radiofrequency ablation. Most of the thermal injury is thought to result from conduction of heat from the surface layer. The purpose of this study was to determine whether lesion depth could be increased by producing direct resistive heating deeper in the tissue with higher radiofrequency power, allowed by cooling the ablation electrode with saline irrigation to prevent the rise in impedance that occurs when the electrode-tissue interface temperature reaches 100 degrees C. METHODS AND RESULTS: In 11 anesthetized dogs, the thigh muscle was exposed and bathed with heparinized canine blood (36 degrees C to 37 degrees C). A 7F catheter, with a central lumen, a 5-mm tip electrode with six irrigation holes, and an internal thermistor, was positioned perpendicular to the thigh muscle and held at a constant contact weight of 10 g. Radiofrequency current was delivered to 145 sites (1) at high constant voltage (66 V) without irrigation (CV group, n = 31), (2) at variable voltage (20 to 66 V) to maintain tip-electrode temperature at 80 degrees C to 90 degrees C without irrigation (temperature-control group, n = 39), and (3) at high CV (66 V) with saline irrigation through the catheter lumen and ablation electrode at 20 mL/min (CV irrigation group, n = 75). Radiofrequency current was applied for 60 seconds but was terminated immediately in the event of an impedance rise > or = 10 omega. Tip-electrode temperature and tissue temperature at depths of 3.5 and 7.0 mm were measured in all three groups (n = 145). In 33 CV irrigation group applications, temperature was also measured with a separate probe at the center (n = 18) or edge (n = 15) of the electrode-tissue interface. In all 31 CV group applications, radiofrequency energy delivery was terminated prematurely (at 11.6 +/- 4.8 seconds) owing to an impedance rise associated with an electrode temperature of 98.8 +/- 2.1 degrees C. All 39 temperature-control applications were delivered for 60 seconds without an impedance rise, but voltage had to be reduced to 38.4 +/- 6.1 V to avoid temperatures > 90 degrees C (mean tip-electrode temperature, 84.5 +/- 1.4 degrees C). In CV irrigation applications, the tip-electrode temperature was not > 48 degrees C (mean, 38.4 +/- 5.1 degrees C) and the electrode-tissue interface temperature was not > 80 degrees C (mean, 69.4 +/- 5.7 degrees C). An abrupt impedance rise with an audible pop and without coagulum occurred in 6 of 75 CV irrigation group applications at 30 to 51 seconds, probably owing to release of steam from below the surface. In the CV and temperature-control group applications, the temperatures at depths of 3.5 (62.1 +/- 15.1 degrees C and 67.9 +/- 7.5 degrees C) and 7.0 mm (40.3 +/- 5.3 degrees C and 48.3 +/- 4.8 degrees C) were always lower than the electrode temperature. Conversely, in CV irrigation group applications, electrode and electrode-tissue interface temperatures were consistently exceeded by the tissue temperature at depths of 3.5 mm (94.7 +/- 9.1 degrees C) and occasionally 7.0 mm (65.1 +/- 9.7 degrees C). Lesion dimensions were smallest in CV group applications (depth, 4.7 +/- 0.6 mm; maximal diameter, 9.8 +/- 0.8 mm; volume, 135 +/- 33 mm3), intermediate in temperature-control group applications (depth, 6.1 +/- 0.5 mm; maximal diameter, 11.3 +/- 0.9 mm; volume, 275 +/- 55 mm3), and largest in CV irrigation group applications (depth, 9.9 +/- 1.1 mm; maximal diameter, 14.3 +/- 1.5 mm; volume, 700 +/- 217 mm3; P < .01, respectively). CONCLUSIONS: Saline irrigation maintains a low electrode-tissue interface temperature during radiofrequency application at high power, which prevents an impedance rise and produces deeper and larger lesions. A higher temperature in the tissue (3.5 mm deep) than at the electrode-tissue interface indicates that direct resistive heating occurred deeper

Microwave ablation of the atrioventricular junction in open-chest dogs.

The use of microwave energy for ablation of the atrioventricular (AV) junction was examined in open-chest dogs. Using a specially designed microwave catheter and a 2450 MHz generator, microwave energy was delivered to the AV junction according to one of two protocols. In protocol 1, increasing amounts of energy were delivered until irreversible AV block occurred. In protocol 2, only two applications of energy were used, one at low energy and the other at an energy found to be high enough to cause irreversible AV block. Each dog received between one and six applications of microwave energy. The amount of energy delivered per application ranged from 25.6 to 311.4 J. No AV block was seen at 59.4 +/- 28.3 J. Reversible AV block was seen with an energy of 120.6 +/- 58 J. Irreversible AV block was seen at 188.1 +/- 75.9 J. Irreversible AV block could be achieved in each animal. There was no difference in the energy required to cause irreversible AV block between the two protocols. The tissue temperature measured near the tip of the microwave catheter was correlated with both the amount of energy delivered and the extent of AV block caused. Histologic examination demonstrated coagulation necrosis of the conduction system. Microwave energy is a feasible alternative energy source for myocardial ablation. Since tissue damage is due exclusively to heating and the resulting rise in temperature can be measured, microwave energy may have advantages over currently existing energy sources in terms of both titrating delivered energy and monitoring the extent of tissue destruction.

Radiofrequency catheter ablation of right atriofascicular (Mahaim) accessory pathways guided by accessory pathway activation potentials.

BACKGROUND: Accessory pathways (APs) exhibiting "Mahaim fiber" physiology (antegrade conduction only, long conduction time, and decremental properties) often connect the lateral right atrium to the right bundle branch (right atriofascicular pathways). Potentials from these pathways have not been recorded previously. The purpose of this study was to determine whether AP activation potentials could be recorded from right atriofascicular APs and to determine whether these potentials could be used to localize a site for catheter ablation. METHODS AND RESULTS: Of 26 consecutive patients referred for catheter ablation of an AP producing a preexcited (antidromic) atrioventricular (AV) reentrant tachycardia having a left bundle branch block pattern with short ventriculoatrial and long AV intervals, 23 (88.5%) were found to have a right atriofascicular AP. During antidromic AV reentrant tachycardia, (1) right atrial extrastimuli (that did not penetrant tachycardia, (1) right atrial extrastimuli (that did not penetrate the AV node) advanced the timing of the next QRS complex, indicating that the AP was connected to the right atrium; (2) earliest antegrade ventricular activation was recorded at the apical right ventricular free wall, and (3) ventricular activation was preceded by activation of the distal right bundle branch, indicating a fascicular insertion or a ventricular insertion close to the terminus of the right bundle branch. A single, discrete, high-frequency AP potential was recorded at the lateral, anterolateral, or posterolateral tricuspid annulus in 22 of the 23 patients 63 +/- 12 milliseconds after the local atrial potential and 83 +/- 23 milliseconds before the local ventricular potential during sinus rhythm. The AP potential was also recorded at sites along the right ventricular free wall between the tricuspid annulus and the site of earliest ventricular activation at the apical region. Programmed atrial stimulation and adenosine each produced prolongation of AP conduction time because of an increase in the A-AP interval and Wenckebach block proximal to the AP potential. Radiofrequency current applied at a site recording the AP potential (tricuspid annulus in 19 patients and right ventricular free wall in 3 patients) eliminated AP conduction in all 22 patients. Tachycardia has not recurred in any patient during 18 +/- 13 months of follow-up. AP conduction was absent in all 9 patients who had a follow-up electrophysiological study 3.8 +/- 1.7 months after ablation. CONCLUSIONS: Right atriofascicular APs consist of two components. The proximal component is located at the lateral, anterolateral, or posterolateral tricuspid annulus, does not generate an AP potential recordable by catheter electrodes, and is responsible for the decremental conduction properties. The "distal" component extends from the tricuspid annulus to the distal right bundle branch at the apical right ventricular free wall and generates a large, high-frequency AP potential that accurately identifies a site for ablation.

Late potentials are unaffected by radiofrequency catheter ablation in patients with ventricular tachycardia.

Reentrant ventricular tachycardia is dependent on an area of myofibers, embedded in scar tissue, which exhibit slow conduction. Late potentials recorded by signal-averaged electrocardiography appear to correspond to these zones of slow conduction and frequently are present in patients with VT. We hypothesized that elimination of inducible VT by catheter-mediated ablation of critical areas of slow conduction would alter late potentials. Four patients underwent catheter ablation in which radiofrequency current was delivered to zones of slow conduction exhibiting isolated mid-diastolic potentials that could not be dissociated from the tachycardia. The four patients had developed VT (cycle length 382 +/- 50 msec; mean +/- SEM) 13-180 months after inferior myocardial infarction. Late potentials were present in each patient before catheter ablation was attempted. Although VT was not inducible in any patient immediately after ablation, late potentials were still present in all four patients and there was no significant difference in the QRS duration (136.5 +/- 4.0 msec postablation; 135.7 +/- 4.5 msec preablation), root mean square voltage in the terminal 40 msec of the QRS (10.0 +/- 1.0 microV postablation; 5.9 +/- 0.4 microV preablation), or in the duration of the low amplitude signal (69.2 +/- 2.0 msec postablation; 62.7 +/- 3.4 msec preablation). At follow-up electrophysiology study performed 14 +/- 7 days after ablation, one of the four patients had inducible VT. In conclusion, late potentials persist even after successful radiofrequency catheter ablation and do not appear to be useful for predicting results of follow-up electrophysiology study.

Radiofrequency catheter ablation of idiopathic left ventricular tachycardia guided by a Purkinje potential.

BACKGROUND: Verapamil-sensitive, idiopathic left ventricular tachycardia (ILVT) with right bundle branch block configuration and left-axis deviation has been suggested to originate from the left posterior fascicle. The purpose of this study was to determine how frequently potentials generated by the Purkinje fiber network (P potential) can be recorded preceding ventricular activation, and the role of the P potential in guiding radiofrequency catheter ablation. METHODS AND RESULTS: Eight patients (mean age, 26 +/- 10 years) with ILVT (cycle length, 346 +/- 59 milliseconds) were studied. Right and left ventricular endocardial mapping during tachycardia identified earliest ventricular activation at the posteroapical left ventricular septum. In all patients, earliest ventricular activation during tachycardia was preceded by a distinct potential. This potential also preceded ventricular activation during sinus rhythm, consistent with activation of a segment of the left posterior fascicle (P potential). The earliest recorded P potential preceded the QRS during tachycardia by 15 to 42 milliseconds (mean, 27 +/- 9 milliseconds). The application of radiofrequency current at 1 to 4 sites (median, 1) eliminated ILVT in all eight patients. In the seven patients with P potentials recorded at multiple sites within the posteroapical septum, ablation was successful at the site of the earliest P potential and unrelated to the timing of ventricular activation. In the remaining patient, ablation was successful at a site recording a late P potential fusing with earliest ventricular activation. During follow-up (1 to 67 months; median, 10.5) ILVT recurred only in the latter patient. Pace mapping during tachycardia at the successful ablation site in four patients produced a similar QRS with stimulus-QRS interval equal to P-QRS interval during tachycardia. However, a similar QRS was obtained by pacing at nearby sites that recorded a later P potential. CONCLUSIONS: These findings support the hypothesis that ILVT originates from the Purkinje network of the left posterior fascicle. A P potential can be recorded at the posteroapical left ventricular septum during ILVT, and ablation is successful at the site recording the earliest P potential. Pace mapping with similar QRS is not specific due to capture of the Purkinje fiber network at a site remote from the origin of the tachycardia.

A functional approach to the preexcitation syndromes.

Electrophysiologic studies have been used to elicit the mechanisms of the preexcitation syndromes and have become a therapeutic tool over the past decade. A thorough understanding of the physiology and anatomy of accessory pathways that are responsible for preexcitation and the associated arrhythmias is necessary before considering the various forms of intervention. The approach to patients with preexcitation syndromes is discussed, with an emphasis on the functional properties of accessory pathways and the associated arrhythmias.

Impact of food on the pharmacokinetics and electrocardiographic effects of sustained release verapamil in normal subjects.

To evaluate the impact of food on the pharmacokinetics and electrocardiographic effects of sustained release (SR) verapamil tablets, 9 healthy men each received 3 single doses of verapamil in a randomized, crossover manner: 10 mg of intravenous verapamil, 240 mg SR verapamil on an empty stomach, and 240 mg SR verapamil with a standardized meal. PR intervals and racemic verapamil serum concentrations were measured serially over 30 hours after administration. The time to peak concentration was longer (7.5 +/- 3.0 vs 4.4 +/- 2.3 hours), resulting in a lower peak verapamil serum concentration (118 +/- 43 vs 175 +/- 50 ng/ml) when SR verapamil was administered with food (p < 0.05). Food tended to decrease the bioavailability of SR verapamil (34 +/- 12 vs 49 +/- 14%), although this difference did not reach statistical significance (p = 0.065). Precipitous or exaggerated release of verapamil from the SR tablet was not observed in any subject during the fasting state. Prolongation of the PR interval paralleled these alterations in serum concentration. The maximal change in the PR interval was greater (21 +/- 8 vs 14 +/- 5%; p < 0.05) when SR verapamil was given in the fasting state. Although an exaggerated verapamil release or effect was not observed, food significantly altered the absorption and electrocardiographic effects of a single dose of SR verapamil. Manipulation of the administration condition may be helpful in achieving desired outcomes.

Treatment of supraventricular tachycardia due to atrioventricular nodal reentry by radiofrequency catheter ablation of slow-pathway conduction.

BACKGROUND: Atrioventricular nodal reentrant tachycardia (AVNRT), the most common form of supraventricular tachycardia, results from conduction through a reentrant circuit comprising fast and slow atrioventricular nodal pathways. Antiarrhythmic-drug therapy is not consistently successful in controlling this rhythm disturbance. Catheter ablation of the fast pathway with radiofrequency current eliminates AVNRT, but it can produce heart block. We hypothesized that catheter ablation of the site of insertion of the slow pathway into the atrium would eliminate AVNRT while leaving normal (fast-pathway) atrioventricular nodal conduction intact. METHODS AND RESULTS: Eighty patients with symptomatic AVNRT were studied. Retrograde slow-pathway conduction (in which the earliest retrograde atrial potential was recorded at the posterior septum, close to the coronary sinus) was present in 33 patients. The retrograde atrial potential was preceded by a potential consistent with activation of the atrial end of the slow pathway (ASP). In 46 of the 47 patients without retrograde slow-pathway conduction, a potential with the same characteristics as the ASP potential was recorded during sinus rhythm. Radiofrequency current delivered through a catheter to the ASP site (in the posteroseptal right atrium or coronary sinus) abolished or modified slow-pathway conduction in 78 patients, eliminating AVNRT without affecting normal atrioventricular nodal conduction. In the single patient without ASP, the application of radiofrequency current to the proximal coronary sinus ablated the fast pathway and AVNRT: Atrioventricular block occurred in one patient (1.3 percent) with left bundle-branch block, after inadvertent ablation of the right bundle branch. AVNRT has not recurred in any patient during a mean (+/- SD) follow-up of 15.5 +/- 11.3 months. Electrophysiologic study 4.3 +/- 3.3 months after ablation in 32 patients demonstrated normal atrioventricular nodal conduction without AVNRT: CONCLUSIONS: Catheter ablation of the atrial end of the slow pathway using radiofrequency current, guided by ASP potentials, can eliminate AVNRT with very little risk of atrioventricular block.