Karen J. Beckman

Catheter ablation of accessory atrioventricular pathways (Wolff-Parkinson-White syndrome) by radiofrequency current.

BACKGROUND Surgical or catheter ablation of accessory pathways by means of high-energy shocks serves as definitive therapy for patients with Wolff-Parkinson-White syndrome but has substantial associated morbidity and mortality. Radiofrequency current, an alternative energy source for ablation, produces smaller lesions without adverse effects remote from the site where current is delivered. We conducted this study to develop catheter techniques for delivering radiofrequency current to reduce morbidity and mortality associated with accessory-pathway ablation. METHODS Radiofrequency current (mean power, 30.9 +/- 5.3 W) was applied through a catheter electrode positioned against the mitral or tricuspid annulus or a branch of the coronary sinus; when possible, delivery was guided by catheter recordings of accessory-pathway activation. Ablation was attempted in 166 patients with 177 accessory pathways (106 pathways in the left free wall, 13 in the anteroseptal region, 43 in the posteroseptal region, and 15 in the right free wall). RESULTS Accessory-pathway conduction was eliminated in 164 of 166 patients (99 percent) by a median of three applications of radiofrequency current. During a mean follow-up (+/- SD) of 8.0 +/- 5.4 months, preexcitation or atrioventricular reentrant tachycardia returned in 15 patients (9 percent). All underwent a second, successful ablation. Electrophysiologic study 3.1 +/- 1.9 months after ablation in 75 patients verified the absence of accessory-pathway conduction in all. Complications of radiofrequency-current application occurred in three patients (1.8 percent): atrioventricular block (one patient), pericarditis (one), and cardiac tamponade (one) after radiofrequency current was applied in a small branch of the coronary sinus. CONCLUSIONS Radiofrequency current is highly effective in ablating accessory pathways, with low morbidity and no mortality.

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

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

BackgroundVerapamil-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 fequently 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 ResultsEight 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. ConclusionsThese findings support the hypothesis that ILVT originates from the Purkinje network of the left posterior fascicle. AP 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.

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.

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 (≤0.5 mV) involved most of the free wall in all patients and contained 2 to 7 dense scars or lines of double potentials, forming 29 narrow channels (width ≤2.7 cm) between scars in all but 1 patient, who had a single scar and only focal AT. All 15 MacroATs were propagated through narrow channels. Ablation within the channel eliminated all 15 MacroATs with 1 to 3 (median 1) radiofrequency applications. Ablation was performed in 9 other channels identified during MacroAT (5 patients) and in 5 channels identified during atrial pacing (2 patients). Conduction block was obtained across 28 of 29 channels. After ablation, reproducible sustained right AT was not induced in any patient. During follow-up (median 13.5 months), new MacroATs, atrial fibrillation, or palpitations occurred in 3 of 16 patients. Conclusions —MacroAT after SR-CHD requires a large area of low voltage containing ≥2 scars forming narrow channels. Ablation within the channels eliminates MacroAT.

Characterization of Reentrant Circuit in Macroreentrant Right Atrial Tachycardia After Surgical Repair of Congenital Heart Disease

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 (≤0.5 mV) involved most of the free wall in all patients and contained 2 to 7 dense scars or lines of double potentials, forming 29 narrow channels (width ≤2.7 cm) between scars in all but 1 patient, who had a single scar and only focal AT. All 15 MacroATs were propagated through narrow channels. Ablation within the channel eliminated all 15 MacroATs with 1 to 3 (median 1) radiofrequency applications. Ablation was performed in 9 other channels identified ...

Electrical Storm Presages Nonsudden Death

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 ≥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 ...

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.

Coronary Sinus-Ventricular Accessory Connections Producing Posteroseptal and Left Posterior Accessory Pathways Incidence and Electrophysiological Identification

Background—The coronary sinus (CS) has a myocardial coat (CSMC) with extensive connections to the left and right atria. We postulated that some posteroseptal and left posterior accessory pathways (CSAPs) result from connections between a cuff of CSMC extending along the middle cardiac vein (MCV) or posterior coronary vein (PCV) and the ventricle. The purpose of the present study was to use CS angiography and mapping to define and determine the incidence of CSAPs and determine the relationship to CS anatomy. Methods and Results—CSAP was defined by accessory pathway (AP) potential or earliest activation in the MCV or PCV and late activation at anular endocardial sites. A CSAP was identified in 171 of 480 patients undergoing ablation of a posteroseptal or left posterior AP. CS angiography revealed a CS diverticulum in 36 (21%) and fusiform or bulbous enlargement of the small cardiac vein, MCV, or CS in 15 (9%) patients. The remaining 120 (70%) patients had an angiographically normal CS. A CSMC extension potential (CSE), like an AP potential, was recorded in the MCV in 98 (82%), in the PCV in 13 (11%), in both the MCV and PCV in 6 (5%), and in the CS in 3 (2%) of 120 patients. CSMC potentials were recorded between the timing of atrial and CSE potentials. Conclusions—CSAPs result from a connection between a CSMC extension (along the MCV or PCV) and the ventricle. The CS is angiographically normal in most patients.

Analysis of implantable cardioverter defibrillator therapy in the Antiarrhythmics Versus Implantable Defibrillators (AVID) Trial

Introduction: The implantable cardioverter defibrillator (ICD) is commonly used to treat patients with documented sustained ventricular tachycardia (VT) or ventricular fibrillation (VF). Arrhythmia recurrence rates in these patients are high, but which patients will receive a therapy and the forms of arrhythmia recurrence (VT or VF) are poorly understood.