Catheter ablation of mitral isthmus ventricular tachycardia using electroanatomically guided linear lesions

Histopathological verification for successful ablation of mitral isthmus ventricular tachycardia complicated with cardiac sarcoidosis

A 68-year-old man died a few days after catheter ablation of drug-resistant, monomorphic ventricular tachycardia (VT) complicated with cardiac sarcoidosis. The diagnosis of mitral isthmus VT was made from electrophysiological observations, including electro-anatomical activation and voltage map, pace-mapping, entrainment mapping and ablation outcome. On autopsy of the heart, sarcoidic lesion with scattered fibrous tissue in the mitral isthmus was non-transmural, and the surviving myocardium serving as the reentry circuit in the endomyocardium was isolated from the adjacent viable epimyocardium, enabling the sustenance of macroreentry across the mitral isthmus. Non-transmural lesions produced by RF delivery created a barrier sufficient to interrupt the myocardial bundles located in the mitral isthmus, eliminating the mitral isthmus VT.

Contrast echocardiography for cardiac radio-frequency ablation

The authors presented a first application of 2-D contrast-enhanced ICE in localizing RF ablation lesions and, more importantly, accurately and reproducibly quantifying their extent and depth within the myocardium in the intact beating heart. Furthermore, the study extended this application and presented, for the first time, a novel method based on contrast-enhanced 3-D ICE to describe details of contiguous linear lesions.

Spiral waves and reentry dynamics in an in vitro model of the healed infarct border zone

RATIONALE

Reentry underlies most ventricular tachycardias (VTs) seen postmyocardial infarction (MI). Mapping studies reveal that the majority of VTs late post-MI arise from the infarct border zone (IBZ).

OBJECTIVE

To investigate reentry dynamics and the role of individual ion channels on reentry in in vitro models of the "healed" IBZ.

METHODS AND RESULTS

We designed in vitro models of the healed IBZ by coculturing skeletal myotubes with neonatal rat ventricular myocytes and performed optical mapping at high temporal and spatial resolution. In culture, neonatal rat ventricular myocytes mature to form striated myocytes and electrically uncoupled skeletal myotubes simulate fibrosis seen in the healed IBZ. High resolution mapping revealed that skeletal myotubes produced localized slowing of conduction velocity (CV), increased dispersion of CV and directional-dependence of activation delay without affecting myocyte excitability. Reentry was easily induced by rapid pacing in cocultures; treatment with lidocaine, a Na(+) channel blocker, significantly decreased reentry rate and CV, increased reentry path length and terminated 30% of reentrant arrhythmias (n=18). In contrast, nitrendipine, an L-type Ca(2+) channel blocker terminated 100% of reentry episodes while increasing reentry cycle length and path length and decreasing reentry CV (n=16). K(+) channel blockers increased reentry action potential duration but infrequently terminated reentry (n=12).

CONCLUSIONS

Cocultures reproduce several architectural and electrophysiological features of the healed IBZ. Reentry termination by L-type Ca(2+) channel, but not Na(+) channel, blockers suggests a greater Ca(2+)-dependence of propagation. These results may help explain the low efficacy of pure Na(+) channel blockers in preventing and terminating clinical VTs late after MI.

Localizing and quantifying ablation lesions in the left ventricle by myocardial contrast echocardiography

INTRODUCTION

The inability to determine the extent and intramural depth of ablation lesions can hamper the success of catheter ablation. The study tested the feasibility of differentiating radiofrequency ablation lesions from normal myocardium and quantifying their dimensions by myocardial contrast echocardiography (MCE).

METHODS AND RESULTS

In 11 normal dogs, we created 14 focal and 4 linear lesions at different left ventricular sites. MCE was performed both before and after ablation by using an intracardiac echocardiography catheter (9 MHz) and infusing contrast microbubbles through the left coronary artery. We initially used two-dimensional MCE to image focal lesions and subsequently three-dimensional MCE to image linear lesions. An independent observer examined the lesion pathology. We found that intracardiac echocardiography alone could not delineate lesion dimensions. However, after ablation, MCE localized the lesions as well-defined, low-contrast areas within the normally opacified myocardium. Lesion dimensions by MCE immediately after ablation and 30 minutes later were similar. In 12 focal lesions, the average maximum depth (5.55 +/- 1.38 mm) and average maximum diameter (10.38 +/- 2.09 mm) by MCE were in excellent agreement with the pathologic depth (5.20 +/- 1.45 mm) and diameter (10.61 +/- 1.67 mm). Two focal lesions could not be detected by MCE and later were found to be superficial. Three-dimensional MCE correctly reconstructed the extent and shape of linear lesions compared to pathology (length: 18.7 +/- 5.7 vs 18.5 +/- 5.6 mm; maximum longitudinal cross-sectional area: 81.2 +/- 9.6 vs 76.0 +/- 10.3 mm2).

CONCLUSION

MCE accurately localized and quantified radiofrequency ablation lesions in the normal left ventricle. This new application of MCE may advance ablation for managing ventricular arrhythmias that involve intramural or epicardial regions by providing instantaneous anatomic feedback on the effects of ablation during catheterization.

Electroanatomic mapping of endocardial right ventricular activation as a guide for catheter ablation in patients with arrhythmogenic right ventricular dysplasia

Arrhythmogenic right ventricular dysplasia is a structural heart disease characterized by fibrofatty degeneration of right ventricular myocardium and arrhythmias of right ventricular origin. The aim of this study was to characterize endocardial right ventricular activation by electroanatomic mapping as a guide for catheter ablation in patients with arrhythmogenic right ventricular dysplasia. Electroanatomic mapping and entrainment procedures were performed in 5 patients with arrhythmogenic right ventricular dysplasia. Endocardial mapping during ventricular tachycardia demonstrated a focal activation pattern with radial spreading of activation from a site of earliest ventricular activation in all directions. Right ventricular activation time (127 +/- 34 ms) was markedly shorter than tachycardia cycle length (415 +/- 92 ms). The site of earliest ventricular activation was found in an aneurysmal outflow tract (n = 2), at the border of aneurysms near the tricuspid annulus (n = 2), and at the apex of the right ventricle (n = 1). Entrainment mapping criteria of these areas of earliest endocardial activity were consistent with exit sites of a reentrant circuit in an area of abnormal myocardium. Fractionated potentials were found 61 +/- 29 ms before the onset of the QRS complex at these sites. Catheter ablation rendered the "clinical" ventricular tachycardia noninducible in four patients but "nonclinical" faster ventricular tachycardias were inducible in three patients. During the follow-up of 7 +/- 3 months after ablation, the frequency of therapies in 4 patients with an implantable cardioverter defibrillator decreased from 49 +/- 61 episodes per month before ablation, to 0.3 +/- 0.5 episodes per month after ablation (P < 0.05). Electroanatomic mapping during ventricular tachycardia facilitates localization of exit sites in relation to aneurysms in diseased right ventricle and may guide catheter ablation in patients with arrhythmogenic right ventricular dysplasia.

Catheter ablation of ventricular tachycardia following myocardial infarction using three-dimensional electroanatomical mapping

One challenge encountered during catheter ablation of postinfarction ventricular tachycardia (VT) is the inducibility of multiple VT morphologies associated with variable hemodynamic instability. The clinical usefulness and safety of a three-dimensional electroanatomical mapping in guiding radiofrequency (RF) catheter ablation of VT, used in parallel with a multichannel recording system, was studied in 28 men (mean age = 63.8 +/- 10.6 years, mean left ventricular ejection fraction = 28% +/- 9%). Three-dimensional voltage maps of the left ventricle were obtained in sinus rhythm with annotation of areas of fractionated or late potentials, zones of slow conduction and/or dense scar with no pacing capture at 10 mA. RF lesions were created either in sinus rhythm or during hemodynamically stable VT within reconstructed critical zones of the circuit. A total of 82 VTs were induced (mean = 2.9 +/- 1.0/patient). Hemodynamically unstable clinical VTs were induced in 5 patients, and clinical or nonclinical unstable VT in 14. Clinical VT was rendered noninducible in 24/28 (85.7%) patients, and monomorphic VT was eliminated in 16/28 (57.1%) patients. The mean procedural time was 258 +/- 82 minutes, and fluoroscopic exposure 13.5 +/- 8.8 minutes. During a mean follow-up period of 10.6 +/- 6.4 months, catheter ablation was repeated in 6 patients for VT recurrences. No significant complications occurred except for a transient cerebral ischemic attack in one patient. In conclusion, electroanatomical mapping assisted the successful and safe catheter ablation of both mappable and nonmappable VTs in a significant proportion of patients after myocardial infarction.

Isthmus characteristics of reentrant ventricular tachycardia after myocardial infarction

BACKGROUND

The reentrant mechanism of postinfarct ventricular tachycardia (VT) has been documented by surgical mapping analysis, but little is known about postinfarct VT circuits and the characteristics of their related protected isthmus with the use of 3D catheter mapping systems.

METHODS AND RESULTS

A 3D electroanatomic mapping was performed in 21 patients with well-tolerated, postinfarct, sustained VT. In total, 33 episodes of tachycardia (mean cycle length 432+/-74 ms) were induced and mapped. Complete maps demonstrated macroreentrant circuits with 1 loop (n=8) or 2 loops (n=25) rotating around a protected isthmus bounded by 2 approximately parallel conduction barriers that consisted of a line of double potentials, a scar area, or the mitral annulus. A total of 26 critical isthmi were identified for the 33 VTs mapped, with the same isthmus being shared by 2 to 4 different tachycardic morphologies in 5 patients. On average, isthmi were 31+/-7 mm long (ranging from 18 to 41 mm) and 16+/-8 mm wide (ranging from 6 to 36 mm) and harbored diastolic electrograms. The isthmus axis was oriented parallel to the mitral annulus plane in perimitral circuits and perpendicular to the mitral annulus plane in all other circuits. Linear radiofrequency ablation performed across the most accessible part of the isthmus prevented the recurrence of tachycardia in 19 patients (90%) with a follow-up at 16+/-8 months.

CONCLUSIONS

Detailed 3D electroanatomic mapping is helpful in reconstructing postinfarct VT circuits and in defining the characteristics of their related protected isthmi. The wide range of isthmus width values supports the need of linear radiofrequency lesions to eliminate the reentrant substrate of postinfarct VTs.

Strategies for catheter ablation of scar-related ventricular tachycardia

Ventricular tachycardia (VT) due to reentry in and around regions of ventricular scar from an old myocardial infarction or cardiomyopathic process is often a difficult management problem. Radiofrequency catheter ablation is an option for controlling frequent VT episodes. Patient and VT characteristics determine the mapping and ablation approach and efficacy. In patients with a VT that is hemodynamically tolerated to allow mapping, prevention of recurrent VT is achieved in 54% to 66% of patients with a procedure related mortality of 1% to 2.7%. Multiple morphologies of monomorphic VT and circuits that are located deep to the endocardium are common problems that reduce efficacy. Mapping to identify target regions for ablation can be difficult if VT is rapid and not tolerated, or not inducible. Ablation of these "unmappable VTs" by designing ablation lines or areas based on the characteristics of the scar as assessed during sinus rhythm, and using approaches to assess global activation from a limited number of beats has been shown to be feasible. Ablation of multiple VTs, epicardial VTs, and poorly tolerated VTs are feasible. Future studies defining efficacy and risks are needed.