Shiro Nakahara

Characterization of the Arrhythmogenic Substrate in Ischemic and Nonischemic Cardiomyopathy: Implications for Catheter Ablation of Hemodynamically Unstable Ventricular Tachycardia

OBJECTIVES The purpose of this study was to compare the characteristics and prevalence of late potentials (LP) in patients with nonischemic cardiomyopathy (NICM) and ischemic cardiomyopathy (ICM) etiologies and evaluate their value as targets for catheter ablation. BACKGROUND LP are frequently found in post-myocardial infarction scars and are useful ablation targets. The relative prevalence and characteristics of LP in patients with NICM is not well understood. METHODS Thirty-three patients with structural heart disease (NICM, n = 16; ICM, n = 17) referred for catheter ablation of ventricular tachycardia were studied. Electroanatomic mapping was performed endocardially (n = 33) and epicardially (n = 19). The LP were defined as low voltage electrograms (<1.5 mV) with onset after the QRS interval. Very late potentials (vLP) were defined as electrograms with onset >100 ms after the QRS. RESULTS We sampled an average of 564 +/- 449 points and 726 +/- 483 points in the left ventricle endocardium and epicardium, respectively. Mean total low voltage area in patients with ICM was 101 +/- 55 cm(2) and 56 +/- 33 cm(2), endocardial and epicardial, respectively, compared with NICM of 55 +/- 41 cm(2) and 53 +/- 28 cm(2), respectively. Within the total low voltage area, vLP were observed more frequently in ICM than in NICM in endocardium (4.1% vs. 1.3%; p = 0.0003) and epicardium (4.3% vs. 2.1%, p = 0.035). An LP-targeted ablation strategy was effective in ICM patients (82% nonrecurrence at 12 +/- 10 months of follow-up), whereas NICM patients had less favorable outcomes (50% at 15 +/- 13 months of follow-up). CONCLUSIONS The contribution of scar to the electrophysiological abnormalities targeted for ablation of unstable ventricular tachycardia differs between ICM and NICM. An approach incorporating LP ablation and pace-mapping had limited success in patients with NICM compared with ICM, and alternative ablation strategies should be considered.

FREEDOM FROM RECURRENT VENTRICULAR TACHYCARDIA AFTER CATHETER ABLATION IS ASSOCIATED WITH IMPROVED SURVIVAL IN PATIENTS WITH STRUCTURAL HEART DISEASE: AN INTERNATIONAL VT ABLATION CENTER COLLABORATIVE GROUP STUDY

BACKGROUND The impact of catheter ablation of ventricular tachycardia (VT) on all-cause mortality remains unknown. OBJECTIVE The purpose of this study was to examine the association between VT recurrence after ablation and survival in patients with scar-related VT. METHODS Analysis of 2061 patients with structural heart disease referred for catheter ablation of scar-related VT from 12 international centers was performed. Data on clinical and procedural variables, VT recurrence, and mortality were analyzed. Kaplan-Meier analysis was used to estimate freedom from recurrent VT, transplant, and death. Cox proportional hazards frailty models were used to analyze the effect of risk factors on VT recurrence and mortality. RESULTS One-year freedom from VT recurrence was 70% (72% in ischemic and 68% in nonischemic cardiomyopathy). Fifty-seven patients (3%) underwent cardiac transplantation, and 216 (10%) died during follow-up. At 1 year, the estimated rate of transplant and/or mortality was 15% (same for ischemic and nonischemic cardiomyopathy). Transplant-free survival was significantly higher in patients without VT recurrence than in those with recurrence (90% vs 71%, P<.001). In multivariable analysis, recurrence of VT after ablation showed the highest risk for transplant and/or mortality [hazard ratio 6.9 (95% CI 5.3-9.0), P<.001]. In patients with ejection fraction <30% and across all New York Heart Association functional classes, improved transplant-free survival was seen in those without VT recurrence. CONCLUSION Catheter ablation of VT in patients with structural heart disease results in 70% freedom from VT recurrence, with an overall transplant and/or mortality rate of 15% at 1 year. Freedom from VT recurrence is associated with improved transplant-free survival, independent of heart failure severity.

Distinguishing epicardial fat from scar: Analysis of electrograms using high-density electroanatomic mapping in a novel porcine infarct model

BACKGROUND The presence of epicardial fat can confound the quantification of scar during transpericardial electroanatomic mapping. The electrogram (EGM) characteristics of epicardial fat have not been systematically compared with infarct scar using gross and histopathological analysis as a gold standard. OBJECTIVE The purpose of this study was to compare the EGM characteristics of epicardial fat with infarct scar. METHODS A closed-chest infarction was created in 40-50 kg pigs by occlusion of the circumflex artery for 150 minutes using an angioplasty balloon. This artery was chosen to minimize any potential overlap of epicardial fat with infarct and to spare any septal involvement. After 4-12 weeks of infarct healing, epicardial mapping was performed. EGMs in low-voltage regions (<1.5 mV) were analyzed, and bipolar amplitude, duration, number of deflections, and the presence of late potentials were recorded. Statistical analysis was performed using unpaired t-test and chi(2) analysis. Gross and histopathological examination was used to confirm areas of fat and infarct scar. RESULTS Seven porcine hearts were analyzed after high-density epicardial mapping (364 +/- 92 points) was performed 48 +/- 19 days after infarction. The mean bipolar EGM amplitude was similar in fat and scar (0.77 +/- 0.34 vs. 0.75 +/- 0.38 mV; P = not significant). The mean EGM duration was longer in scar than in fat (68.8 +/- 18.9 vs. 50.1 +/- 11.6 ms; P <.0001) and exhibited more fractionation (8.5 +/- 3.1 vs. 4.7 +/- 1.8 deflections; P <.0001). The presence of late potentials was 99% specific for scar. Further, areas of fat >4 mm in thickness registered low-voltage bipolar EGMs. CONCLUSION Scar from healed myocardial infarction exhibits more fractionation and longer EGM duration when compared with fat. Late potentials are highly specific for locating infarct scars.

Hybrid procedures for epicardial catheter ablation of ventricular tachycardia: Value of surgical access

BACKGROUND Prior chest surgery limits the ability to obtain epicardial access in patients referred for catheter ablation of ventricular tachycardia (VT). OBJECTIVE The purpose of this study was to describe the utility of different surgical approaches to access the epicardium for VT ablation. METHODS Clinical data of 14 patients with drug-refractory VT who underwent hybrid surgical epicardial access for catheter mapping and ablation in the electrophysiology lab were reviewed. Baseline patient and procedural characteristics including access, exposure, mapping techniques, and ablation were analyzed. RESULTS Of a total of 14 patients (age 63.2 ± 10.3 years), 11 had a subxiphoid window performed, and three patients underwent limited anterior thoracotomy to access the epicardium. The indication for surgical access was prior cardiac surgery (n = 12), previous failed epicardial access (n = 1), and ablation in close proximity to the coronary arteries and phrenic nerve (n = 1). Mapping in patients with subxiphoid surgical access was limited to the inferior and diaphragmatic surface of the heart extending posteriorly to the basal lateral wall. With limited anterior thoracotomy, access to the apex, anterior, and mid to apical anterolateral walls was obtained. In these regions, adhesions were more severe and repeat entry into the epicardial region at a different intercostal level was needed in two of three patients. CONCLUSION Surgical access with subxiphoid window and limited anterior thoracotomy in the electrophysiology lab is feasible and safe. The surgical approach can be tailored to the region of interest in the ventricle to be mapped and ablated.

Distribution of late potentials within infarct scars assessed by ultra high-density mapping.

BACKGROUND Late potential (LP) electrograms represent areas of slow conduction and are often sites critical to reentrant tachycardia circuits. The distribution of LPs within infarct scar is not known. OBJECTIVE The purpose of this study was to delineate infarct heterogeneity using ultra high-density mapping and to determine the location of LPs with respect to scar architecture. METHODS Detailed endocardial (n = 21) and epicardial (n = 8) ultra high-density mapping was performed to delineate the substrate for ventricular tachycardia (VT) in 21 patients with ischemic cardiomyopathy. LP was defined as a low-voltage electrogram (< 1.5 mV) with distinct onset after the QRS. Very late potentials (vLPs) were classified as LPs with onset > 100 ms after the QRS. RESULTS A mean of 787 ± 391 and 810 ± 375 points in the LV endocardium and epicardium were sampled. Multipolar mapping identified heterogeneous islets (HIs) with relatively preserved electrogram amplitudes (≥ 0.51 mv) within dense scar (8.5 ± 4.9/4.5 ± 2.6 HIs per endocardium/epicardium) in all patients. In maps on which putative VT isthmuses were identified (25/29), 57% of vLP were recorded in or adjacent to HI. An LP-targeted ablation strategy combined with pace mapping achieved acute success in all patients (complete success in 52% and partial success in 48%). After 15 ± 7 months, 65% of patients remained free of VT episodes. CONCLUSION Ultra high-density mapping with a multipolar catheter facilitates the delineation of heterogeneous scar architecture at higher resolution. Electrograms within and adjacent to HIs have a higher incidence of vLP, and these sites are frequently critical to reentry. These findings have important implications for substrate-based ablation strategies.

Intra-pericardial balloon retraction of the left atrium: A novel method to prevent esophageal injury during catheter ablation

Catheter ablation for atrial fibrillation (AF) is a useful treatment option for this common arrhythmia, reducing morbidity compared to drug therapy1. Methods and technology have improved in recent years, and it is has even been offered as first-line therapy in a few experienced centers2. Despite the promise of catheter ablation, a variety of serious complications have been reported, including pulmonary vein stenosis, cardiac perforation, thromboembolism, vascular complications, and phrenic nerve injury. Atrioesophageal fistula, thought to result from thermal injury of the esophagus due to its close apposition to the posterior left atrial (LA) wall3, is a rare but often fatal complication of catheter ablation for AF4. Several methods have been proposed for detecting and avoiding esophageal injury during left atrial catheter ablation, including fluoroscopic contrast visualization of the esophagus during the procedure5, which provides a rough guide but may underestimate the size of the esophagus6. Temperature monitoring also offers a means of detecting intraprocedural esophageal heating so radiofrequency application at that site can be discontinued7, 8. However, only a few active techniques for esophageal protection have been proposed, including mechanical deflection of the esophagus9 and active esophageal cooling10. These have not been widely used during ablation procedures; most experts advise simply limiting energy delivery near the esophagus and monitoring for heating. Our group has previously used an intra-pericardial balloon to protect the phrenic nerve during a catheter ablation procedure11. In the current communication, we demonstrate a novel technique, inflating an intra-pericardial balloon between the left atrium and esophagus to prevent esophageal injury during ablation of the posterior LA wall.

Ultra high-density multipolar mapping with double ventricular access: A novel technique for ablation of ventricular tachycardia

Ultra High‐Density Multipolar Mapping With Double Ventricular Access. Background: Analogous to the use of circular loop catheters to guide ablation around the pulmonary veins, it may be advantageous to use a multipolar catheter in the ventricle for rapid mapping and to guide ablation. We describe a technique using double access into the left ventricle for multipolar electroanatomic mapping and ablation of scar‐mediated ventricular tachycardia (VT).

Intrapericardial balloon placement for prevention of collateral injury during catheter ablation of the left atrium in a porcine model

BACKGROUND Catheter ablation of the left atrium (LA) is associated with potential collateral injury to surrounding structures, especially the esophagus and the right phrenic nerve (PN). OBJECTIVES The purpose of this study was to evaluate the efficacy and feasibility of intrapericardial balloon placement (IPBP) for the protection of collateral structures adjacent to the LA. METHODS Electroanatomic mapping was performed in porcine hearts using a transseptal endocardial approach in eight swine weighing 40-50 kg. An intrapericardial balloon was inflated in the oblique sinus, via percutaneous epicardial access, to displace the esophagus. Similarly, with the balloon positioned in the transverse sinus, IPBP was used to displace the right PN. Esophageal temperature was monitored while endocardial radiofrequency (RF) energy was delivered to the distal inferior PV. RESULTS In all cases, balloon placement was successful with no significant effects on hemodynamic function. Balloon inflation increased the distance between the esophagus and posterior LA by 12.3 +/- 4.0 mm. IPBP significantly attenuated increases in luminal esophageal temperature during endocardial RF application (6.1 +/- 2.4 degrees C vs. 1.2 +/- 1.1 degrees C; P<.0001). High-output endocardial pacing from the right superior pulmonary vein ostium stimulated PN activity. After displacement of the right PN with IPBP, PN capture was abolished in 30 (91%) of 33 sites. CONCLUSIONS These findings demonstrate that in an animal model, IPBP is feasible in the setting of catheter ablation procedures and has the potential to decrease the risk of collateral damage to the esophagus and PN during LA ablation.

Characterization of myocardial scars: Electrophysiological imaging correlates in a porcine infarct model

BACKGROUND Definition of myocardial scars as identified by electroanatomic mapping is integral to catheter ablation of ventricular tachycardia (VT). Myocardial imaging can also identify scars prior to ablation. However, the relationship between imaging and voltage mapping is not well characterized. OBJECTIVE The purpose of this study was to verify the anatomic location and heterogeneity of scars as obtained by electroanatomic mapping with contrast-enhanced MRI (CeMRI) and histopathology, and to characterize the distribution of late potentials in a chronic porcine infarct model. METHODS In vivo 3-dimensional cardiac CeMRI was performed in 5 infarcted porcine hearts. High-density electroanatomic mapping was used to generate epicardial and endocardial voltage maps. Scar surface area and position on CeMRI were then correlated with voltage maps. Locations of late potentials were subsequently identified. These were classified according to their duration and fractionation. All hearts underwent histopathological examination after mapping. RESULTS The total dense scar surface area and location on CeMRI correlated to the total epicardial and endocardial surface scar on electroanatomic maps. Electroanatomic mapping (average of 1,532 ± 480 points per infarcted heart) showed that fractionated late potentials were more common in dense scars (<0.50 mV) as compared with border zone regions (0.51 to 1.5 mV), and were more commonly observed on the epicardium. CONCLUSION In vivo, CeMRI can identify areas of transmural and nontransmural dense scars. Fractionated late diastolic potentials are more common on the epicardium than the endocardium in dense scar. These findings have implications for catheter ablation of VT and for targeting the delivery of future therapies to scarred regions.

Accuracy of combined endocardial and epicardial electroanatomic mapping of a reperfused porcine infarct model: A comparison of electrofield and magnetic systems with histopathologic correlation

BACKGROUND Contact mapping of the ventricle with NAVX has not been validated. OBJECTIVE This study sought to compare the accuracy of infarct mapping between NAVX and CARTO using a histopathologic gold standard. METHODS A closed-chest porcine infarction model was created by circumflex artery occlusion. After 4 to 12 weeks, 7 subjects underwent high-density endocardial and epicardial mapping using CARTO (Biosense Webster, Diamond Bar, California) and NAVX (St. Jude Medical, St. Paul, Minnesota) mapping systems. After mapping, animals were euthanized and histopathologic examination was used to quantify areas of scar at depths of 1 to 4 mm. RESULTS Using a single-point acquisition approach with CARTO and a multipoint acquisition approach with the NAVX, endocardial and epicardial maps created using CARTO consisted of 360 ± 121 points performed in 54 ± 23 minutes/361 ± 90 points in 41 ± 13 minutes compared with 697 ± 132 points in 35 ± 8 minutes/1,303 ± 207 points in 30 ± 11 minutes using NAVX. At a 2-mm depth from the endocardial and epicardial surface, the mean scar area quantified by histopathology was 9.5 ± 8.7 cm(2) and 6.2 ± 4.8 cm(2), respectively. Correlation between histopathology and electroanatomic maps was excellent (r = 0.88, CARTO and 0.92, NAVX). Correlation between scar area determined by CARTO and NAVX was good (r = 0.88, P <.0001). CONCLUSION Balloon occlusion-reperfusion of the circumflex artery creates a localized patchy infarction in the inferolateral wall. Multipolar mapping achieves higher density in a shorter period of time and increases the detection of late potentials. A strong correlation between CARTO and NAVX exists, and both systems demonstrate good correlation with histopathologic quantification of scar.