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Background: Assessment of origin of ventricular tachycardias (VTs) arising from epicardial vs endocardial sites are largely challenged by the available criteria and etiology of cardiomyopathy. Current electrocardiographic (ECG) criteria based on 12-lead ECG have varying sensitivity and specificity based on site of origin and etiology of cardiomyopathy., Objectives: This study sought to test the hypothesis that epicardial VT has a slower initial rate of depolarization than endocardial VT., Methods: We developed a method that takes advantage of the fact that electrical conduction is faster through the cardiac conduction system than the myocardium, and that the conduction system is primarily an endocardial structure. The technique calculated the rate of change in the initial VT depolarization from a signal-averaged 12-lead ECG. We hypothesized that the rate of change of depolarization in endocardial VT would be faster than epicardial. We assessed by applying this technique among 26 patients with VT in nonischemic cardiomyopathy patients., Results: When comparing patients with VTs ablated using epicardial and endocardial approaches, the rate of change of depolarization was found to be significantly slower in epicardial (6.3 ± 3.1 mV/s vs 11.4 ± 3.7 mV/s; P < 0.05). Statistical significance was found when averaging all 12 ECG leads and the limb leads, but not the precordial leads. Follow up analysis by calculation of a receiver-operating characteristic curve demonstrated that this analysis provides a strong prediction if a VT is epicardial in origin (AUC range 0.72-0.88). Slower rate of change of depolarization had high sensitivity and specificity for prediction of epicardial VT., Conclusions: This study demonstrates that depolarization rate analysis is a potential technique to predict if a VT is epicardial in nature., Competing Interests: Funding Support and Author Disclosures This work was supported in part by the University of Minnesota’s Medical School Academic Investment Education Program grant and the Institute for Engineering in Medicine. Dr Prisco is funded by the National Institutes of Health T32 HL144472. All other authors have reported that they have no relationships relevant to the contents of this paper to disclose., (Copyright © 2024 American College of Cardiology Foundation. All rights reserved.)

Competing Interests: Funding Support and Author Disclosures This work was made possible by support from National Institutes of Health grant OT2OD023848 to Dr Shivkumar. All other authors have reported that they have no relationships relevant to the contents of this paper to disclose.

The pericardium of the human heart has received increased attention in recent times due to interest in the epicardial approach for cardiac interventions to treat cardiac arrhythmias refractory to conventional endocardial approaches. To support further clinical application of this technique, it is fundamental to appreciate the living anatomy of the pericardial space, as well as its relationships to the surrounding structures. The anatomy of the pericardial space, however, is extremely difficult regions to visualize. This is due to its complex 3-dimensionality, and the "potential" nature of the space, which becomes obvious only when there is collection of pericardial fluid. This potential space, which is bounded by the epicardium and pericardium, can now be visualized by special techniques as we now report, permitting appreciation of its living morphology. Current sources of knowledge are limited to the dissection images, surgical images, and/or illustrations, which are not necessarily precise or sufficient to provide relevant comprehensive anatomical knowledge to those undertaking the epicardial approach. The authors demonstrate, for the first time to their knowledge, the 3-dimensional living anatomy of the pericardial space relative to its surrounding structures. They also provide correlative anatomy of the left sternocostal triangle as a common site for subxiphoid access. The authors anticipate their report serving as a tool for education of imaging and interventional specialists., Competing Interests: Funding Support and Author Disclosures This work was made possible by support from National Institutes of Health grant OT2OD023848 to Dr Shivkumar. The authors have reported that they have no relationships relevant to the contents of this paper to disclose., (Copyright © 2021 American College of Cardiology Foundation. Published by Elsevier Inc. All rights reserved.)

The pericardial cavity and its boundaries are formed by the reflections of the visceral and parietal pericardial layers. This space is an integral access point for epicardial interventions. As the pericardial layers reflect over the great vessels and the heart, they form sinuses and recesses, which restrict catheter movement. The epicardial vasculature is also important when performing nearby catheter ablation. The phrenic nerve and esophagus are other important structures to appreciate so as to avoid collateral injury. In addition, the Larrey space, or left sternocostal triangle, is a key avascular window through which pericardial access can be safely achieved., Competing Interests: Disclosure None., (Copyright © 2020 Elsevier Inc. All rights reserved.)

Access to the epicardial space is fundamental to several cardiac procedures. While traditional indications include catheter ablation of ventricular arrhythmias and accessory pathways, novel indications include left atrial appendage occlusion, esophageal protection, mapping and ablation during atrial fibrillation procedures, implantation of epicardial pacing leads, and phrenic nerve displacement to facilitate safe ablation of atrial and ventricular arrhythmias. Accessing the epicardial space safely is a major challenge requiring intimate knowledge of cardiac anatomy, extensive training, and expertise. Over the past years, multiple technological advances have led to significant improvements in epicardial access success and safety. Important examples of such advances include CO 2 insufflation through the coronary sinus or the right atrial appendage, pressure sensor needle, computed tomography, cardiac magnetic resonance, and electroanatomic mapping-guided epicardial access. In addition, we provide special maneuvers to minimize inadvertent right ventricular perforation., (Copyright © 2019 Heart Rhythm Society. Published by Elsevier Inc. All rights reserved.)

Background: Pericardial adhesions can prevent epicardial access and restrict catheter movement during mapping and ablation of ventricular tachycardia (VT). The incidence of adhesions in patients without prior cardiac surgery or clinically evident pericarditis is not known., Objective: To describe the incidence of pericardial adhesions and explore their impact in patients without prior cardiac surgery or pericarditis., Methods: A retrospective search of our ablation database containing patients who underwent epicardial ablation for VT was undertaken. Adhesions were diagnosed with routine contrast pericardiography after pericardial entry. Demographics and long-term outcomes were compared between patients with and without adhesions., Results: Between 2004 and 2016, successful epicardial entry was achieved in 188 of 192 attempts (98%). In 155 first-time epicardial access attempts, pericardial adhesions were diagnosed in 13 (8%). When comparing baseline demographics, there was no significant difference. However, adhesions tended to occur more frequently with severe renal impairment (2% of patients without adhesions vs 15% of patients with adhesions, P = .07). No patient with a structurally normal heart had adhesions present. Adhesions were associated with limited epicardial mapping (3% of patients without adhesions vs 85% of patients with adhesions, P < .001) and lower short-term procedural success (68% of patients without adhesions vs 46% of patients with adhesions, P = .02), but complication rates were similar. The presence of adhesions did not translate into lower VT-free survival (P = .64) or freedom from a combined end point of VT recurrence, death, or transplant at 1 year (P = .93)., Conclusion: Adhesions may be unexpectedly encountered in patients without prior cardiac surgery or pericarditis. When present, they can limit mapping and may be associated with lower short-term success. Larger studies are required to determine their impact on long-term outcomes., (Copyright © 2017 Heart Rhythm Society. Published by Elsevier Inc. All rights reserved.)

Background: Catheter ablation in the right ventricular outflow tract (RVOT) may modify the electrophysiologic substrate for recurrent ventricular tachycardia/ventricular fibrillation (VT/VF) in patients with Brugada syndrome (BrS)., Objective: The purpose of this study was to investigate the mechanism and arrhythmogenic substrate of VT/VF and to evaluate the long-term outcomes of catheter ablation in patients with BrS., Methods: Eleven consecutive patients with BrS referred to 2 academic medical centers underwent combined epicardial-endocardial electroanatomic mapping. Catheter ablation was performed in regions of localized conduction slowing. Transmural dispersion of late activation was calculated as the difference between the latest activation between epicardium and endocardium, and low-voltage areas were analyzed., Results: Eleven patients met diagnostic criteria for BrS (spontaneous type 1, n = 9; Na channel provocation = 2). All patients were found to have a localized region in the anterior epicardial RVOT with conduction slowing evidenced by prolonged electrogram duration (78.79 ± 19.87 ms vs 58.93 ± 10.11 ms in epicardial right ventricle, and 59.87 ± 12.61 ms in endocardial RVOT, P <.005, respectively) with variable low voltage (0.97 ± 0.48 mV; median scar area 19.8 ± 25.9 cm 2 ). Epicardial ablation resulted in normalization of spontaneous type 1 Brugada ECG pattern in all patients, and 73% were free from VT/VF at 25 ± 11 months., Conclusion: Prolonged electrograms localized to epicardial RVOT with variable low voltage were identified in all patients with BrS. J-point and ST-segment elevation correlated with greater transmural dispersion of late activation and was independent of total low-voltage area. Despite normalization of spontaneous type 1 pattern in all patients after ablation, recurrence was still observed, suggesting the implantable cardioverter-defibrillator as the cornerstone therapy for BrS., (Copyright © 2016 Heart Rhythm Society. All rights reserved.)

Introduction: Reversible premature ventricular complexes-induced cardiomyopathy (PVC-CMP) is a well-described, multi-factorial entity. Single predictors, such as PVC burden or QRS duration, may not apply equally to all patients in contemporary unselected populations including patients with structural heart disease (SHD) or with particular origin such as epicardial (EPI) PVC. We sought to evaluate clinical criteria associated with PVC-CMP notably focusing on the EPI origin impact and ECG recognition and the value of a new composite predictor of PVC-CMP, the PVC-CMP-Index., Methods and Results: We studied 107 consecutive patients (69 men; mean age = 56 ± 16 years) with frequent PVC (23.1 ± 11.5%) referred for PVC ablation. Thirty-six patients (33.6%) had an underlying SHD and 25 patients (23.4%) an EPI PVC origin. After a mean follow-up of 22.7 ± 15.3 months, 72.9% achieved a long-term successful ablation and 54.2% had PVC-CMP. PVC-CMP prevalence was significantly higher in patients with an EPI compared to endocardial PVC focus (84.0% vs. 45.1%, respectively, P < 0.001). EPI PVC origin (OR = 68.7 IC95% [3.5-1363], P = 0.005), as well as SHD (OR = 12.3 IC95% [1.6-92.6], P = 0.015), was independent predictor of PVC-CMP. While PVC burden (AUC = 0.78) or PVC-QRS width (AUC = 0.68) independently predicted PVC-CMP, the PVC-CMP-Index (values ≥39) defined as: PVC burden (0-1) × PVC-QRS width (milliseconds) × a constant C (1.28 for SHD or 2 for ECG suggesting EPI origin based on our ECG 3-step algorithm), highly correlated with PVC-CMP (AUC = 0.91, sensitivity = 93%, specificity = 80%)., Conclusion: We developed a new index, which incorporates PVC burden, QRS width, and presence of SHD or suspected EPI origin that best predicted PVC-CMP., (© 2016 Wiley Periodicals, Inc.)

Epicardial mapping and ablation via a percutaneous subxiphoid technique has been instrumental in improving the working understanding of complex myocardial scars in various arrhythmogenic substrates. Endocardial ablation alone may not be sufficient in patients with ischemic cardiomyopathy, dilated cardiomyopathy, arrhythmogenic right ventricular cardiomyopathy, hypertrophic cardiomyopathy, and Chagas disease to prevent recurrent ventricular tachycardia. Multiple observational studies have demonstrated greater freedom from recurrence with adjunctive epicardial ablation compared with endocardial ablation alone. While epicardial ablation is performed predominantly at tertiary referral centers, knowledge of the technical approach, clinical indications, and potential complications is imperative to maximizing clinical success and patient safety. In 1996, Sosa and colleagues modified the pericardiocentesis technique to enable percutaneous access to the pericardial space for mapping and catheter ablation of ventricular tachycardia.1 Originally developed for patients with epicardial scarring due to chagasic cardiomyopathy and patients with ischemic cardiomyopathy refractory to endocardial ablationm,2,3 this approach has since become an essential part of the armamentarium for the treatment of ventricular tachycardia. Myocardial scars are three-dimensionally complex with varying degrees of transmurality, and the ability to map and ablate the epicardial surface has contributed to a greater understanding of scar-related VT in postinfarction cardiomyopathy and nonischemic substrates including idiopathic dilated cardiomyopathy, arrhythmogenic right ventricular cardiomyopathy, hypertrophic cardiomyopathy, and chagasic cardiomyopathy. In this review, we highlight the percutaneous approach and discuss clinical indications and potential complications.

Background: T-peak to T-end interval (Tp-e) is an independent marker of sudden cardiac death. Modulation of Tp-e by sympathetic nerve activation and circulating norepinephrine is not well understood. The purpose of this study was to characterize endocardial and epicardial dispersion of repolarization (DOR) and its effects on Tp-e with sympathetic activation., Methods and Results: In Yorkshire pigs (n=13), a sternotomy was performed and the heart and bilateral stellate ganglia were exposed. A 56-electrode sock and 64-electrode basket catheter were placed around the epicardium and in the left ventricle (LV), respectively. Activation recovery interval, DOR, defined as variance in repolarization time, and Tp-e were assessed before and after left, right, and bilateral stellate ganglia stimulation and norepinephrine infusion. LV endocardial and epicardial activation recovery intervals significantly decreased, and LV endocardial and epicardial DOR increased during sympathetic nerve stimulation. There were no LV epicardial versus endocardial differences in activation recovery interval during sympathetic stimulation, and regional endocardial activation recovery interval patterns were similar to the epicardium. Tp-e prolonged during left (from 40.4±2.2 ms to 92.4±12.4 ms; P<0.01), right (from 47.7±2.6 ms to 80.7±11.5 ms; P<0.01), and bilateral (from 47.5±2.8 ms to 78.1±9.8 ms; P<0.01) stellate stimulation and strongly correlated with whole heart DOR during stimulation (P<0.001, R=0.86). Of note, norepinephrine infusion did not increase DOR or Tp-e., Conclusions: Regional patterns of LV endocardial sympathetic innervation are similar to that of LV epicardium. Tp-e correlated with whole heart DOR during sympathetic nerve activation. Circulating norepinephrine did not affect DOR or Tp-e., (© 2014 American Heart Association, Inc.)

Background: There is a paucity of data on biophysical parameters during radiofrequency ablation of scar-mediated ventricular tachycardia (VT)., Methods and Results: Data were collected from consecutive patients undergoing VT ablation with open-irrigation. Complete data were available for 372 lesions in 21 patients. The frequency of biophysical parameter changes were: >10Ω reduction (80%), bipolar EGM reduction (69%), while loss of capture was uncommon (32%). Unipolar injury current was seen in 72% of radiofrequency applications. Both EGM reduction and impedance drop were seen in 57% and a change in all 3 parameters was seen in only 20% of lesions. Late potentials were eliminated in 33%, reduced/modified in 56%, and remained after ablation in 11%. Epicardial lesions exhibited an impedance drop (90% vs. 76%, P = 0.002) and loss of capture (46% vs. 27%, P < 0.001) more frequently than endocardial lesions. Lesions delivered manually exhibited a >10Ω impedance drop (83% vs. 71%, P = 0.02) and an EGM reduction (71% vs. 40%, P < 0.001) more frequently than lesions applied using magnetic navigation, although loss of capture, elimination of LPs, and a change in all 3 parameters were similarly observed., Conclusions: VT ablation is inefficient as the majority of radiofrequency lesions do not achieve more than one targeted biophysical parameter. Only one-third of RF applications targeted at LPs result in complete elimination. Epicardial ablation within scar may be more effective than endocardial lesions, and lesions applied manually may be more effective than lesions applied using magnetic navigation. New technologies directed at identifying and optimizing ablation effectiveness in scar are clinically warranted., (© 2014 Wiley Periodicals, Inc.)

Management of patients with nonischemic cardiomyopathy (NICM) and ventricular tachycardia (VT) remains challenging. The role of catheter ablation for VT continues to evolve for these patients. Prior reports have described the location of the arrhythmogenic substrate for patients with NICM to be frequently located along the basal left ventricle, with an epicardial predilection. Furthermore, predictors for identifying whether mapping the endocardium or epicardial surface of the heart have been identified for improved success of VT ablation in this patient population. This chapter will review the latest advances in catheter ablation of ventricular tachycardia in patients with NICM.

Background: In patients with arrhythmogenic right ventricular dysplasia/cardiomyopathy, freedom from ventricular arrhythmias (VAs) after endocardial ablation is limited. We compared the long-term freedom from recurrent VAs by using endocardial-alone ablation versus endo-epicardial substrate-based ablation., Methods and Results: Forty-nine patients with arrhythmogenic right ventricular dysplasia/cardiomyopathy undergoing ablation of ventricular tachycardia (VT) were divided into 2 groups: endocardial-alone ablation (group 1, n = 23) and endo-epicardial ablation (group 2, n = 26). All patients had an implantable cardioverter-defibrillator (ICD). Conventional and 3D mappings were used to determine the mechanism of induced VTs and to identify area of "scar" or "abnormal" myocardium. All critical sites responsible for VTs and points with "abnormal" potential were targeted for ablation from endocardium (group 1) or from both endocardium and epicardium (group 2). The procedural end point was noninducibility of sustained, monomorphic VT with isoproterenol. The presence of frequent premature ventricular contractions at the end of ablation was recorded. Patients were followed up by ECG, Holter, and ICD interrogation. After a follow-up of at least 3 years, freedom from VAs or ICD therapy was 52.2% (12/23) in group 1 and 84.6% (22/26) in group 2 (P = 0.029), with 21.7% (5/23) and 69.2% (18/26) patients off antiarrhythmic drugs (P < 0.001), respectively. Compared with patients with no premature ventricular contractions after ablation, patients with frequent premature ventricular contractions after ablation were more likely to have VA recurrence/ICD therapy [3/33 (9%) versus 12/16 (75%); log-rank P<0.001]., Conclusions: An endo-epicardial-based ablation strategy achieves higher long-term freedom from recurrent VAs off antiarrhythmic therapy in patients with arrhythmogenic right ventricular dysplasia/cardiomyopathy when compared with endocardial-alone ablation. The presence of ≥ 10 premature ventricular contractions per minute after ablation is associated with more VA recurrence.

Background: Electrophysiological properties of the atrial endocardium compared to epicardium are not well understood. The purpose of this study was to compare the electrophysiological properties and vulnerability to arrhythmia induction from these regions., Methods and Results: Transseptal endocardial and percutaneous epicardial mapping were performed in a porcine model (n = 7). Two opposing 4-mm electrophysiological catheters were positioned endocardially and epicardially. A circular mapping catheter (CMC) was positioned at the ostium of the common inferior pulmonary vein (CIPV) recording left atrial (LA)-PV potentials. Endocardial and epicardial effective refractory periods (ERPs) at two basic cycle lengths (CLs) of 600 and 400 ms were recorded from four anatomic locations (CIPV, LA appendage, right superior PV, and LA posterior wall). Atrial repetitive response (ARR) induction was also tested from endocardial and epicardial sites. Overall, 254 ERP measurements (mean 36.3 per animal) and 84 induction attempts (mean 12 per animal) were performed. The ERP was significantly shorter in the epicardium compared to the endocardium at basic CL of 400 ms (P = 0.006) but not at CL of 600 ms (P = 0.2). In addition, only the epicardium demonstrated ERP shortening when the CL of the basic drive was shortened (P = 0.03). ARR could be induced more often from the epicardium (P = 0.002) and fibrillatory activity with epicardial/endocardial dissociation was recorded (n = 3). Also, the earliest PV activation site on the CMC was noted to be different in 16.5% of cases during epicardial and endocardial pacing., Conclusion: The electrophysiological characteristics of the atrial epicardium are different from the endocardium with a shorter ERP and more frequent ARR induction by programed stimulation., (©2010, The Authors. Journal compilation ©2010 Wiley Periodicals, Inc.)

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., (Copyright © 2010. Published by Elsevier Inc.)

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.

Background: Percutaneous pericardial access, epicardial mapping, and ablation have been used successfully for catheter ablation procedures., Objectives: The purpose of this study was to evaluate the safety and feasibility of closed-chest direct epicardial ultrasound imaging for aiding cardiac catheter ablation procedures., Methods: An intracardiac ultrasound catheter was used for closed-chest epicardial imaging of the heart in 10 patients undergoing percutaneous epicardial access for catheter ablation. All patients underwent concomitant intracardiac echocardiography and preprocedural transesophageal echocardiography. Using a double-wire technique, two sheaths were placed in the pericardium, and a phased-array ultrasound catheter was manipulated within the pericardial sinuses for imaging., Results: Multiple images from varying angles were obtained for catheter navigation. Notably, image stability was excellent, and structures such as the left atrial appendage were seen in great detail. No complications resulting from use of the ultrasound catheter in the pericardium occurred, and no restriction of movement due to the presence of the additional catheter in the pericardial space was observed. Wall motion was correlated to voltage maps in five patients and showed that areas of scars correlated with wall-motion abnormalities. Normal wall-motion score correlated to sensed signals of 4.2 +/- 0.3 mV (normal myocardium >1.5 mV), and scores >1 correlated to areas with signals <0.5 mV in that territory)., Conclusion: Intrapericardial imaging using an ultrasound catheter is feasible and safe and has the potential to provide additional valuable information for complex ablation procedures.

Background: Percutaneous epicardial mapping has been used for ablation of recurrent ventricular tachycardia (VT)., Objectives: The purpose of this study was to use a combined epicardial and endocardial mapping strategy to delineate the myocardial substrate for recurrent VT in both ischemic (n = 12) and nonischemic cardiomyopathy (n = 8), and to define the role of epicardial ablation., Methods: Electroanatomic mapping was performed in 20 patients. High-density voltage maps were obtained by acquiring both endocardial and epicardial electrograms. Electrograms derived from six patients with structurally normal hearts were used as controls. A total of 26 VTs were targeted in the 20 patients., Results: Most VTs (23/26 [88.5%]) were hemodynamically unstable. In patients with ischemic cardiomyopathy, the extent of endocardial scar was greater than epicardial scar. A definable pattern of scar could not be demonstrated in nonischemic cardiomyopathy. Pathologic examination of explanted hearts in two patients with nonischemic cardiomyopathy demonstrated that low-voltage areas were not always predictive of scarred myocardium. A substrate-based approach was used for catheter ablation. Catheter ablation was performed on the endocardium in all patients; additional epicardial delivery of radiofrequency energy was required in 8 (40%) of 20 patients for successful ablation. During follow-up (12 +/- 4 months), 15 (75%) of 20 patients have been arrhythmia-free., Conclusion: Patients with ischemic cardiomyopathy tend to have a larger endocardial than epicardial scar. Use of epicardial and endocardial electroanatomic mapping to define the full extent of myocardial scars allows successful catheter ablation in patients with hemodynamically unstable VTs.

Objectives: The aim of this study was to define the role of percutaneous epicardial mapping for the ablation of previous failed ablation of accessory pathways., Background: Cardiac surgery is the only curative option for failed radiofrequency (RF) catheter ablation of accessory pathway (AP)-mediated tachycardias. We investigated a combined percutaneous epicardial and endocardial approach for failed AP ablations., Methods: We present our experience in a series of 6 cases (7 APs) with previous failed attempts at catheter ablation (median 2 attempts, range 1-4) and persistent symptomatic tachycardias. Endocardial mapping of the APs was performed using conventional techniques. Sites with local electrograms suggestive of AP location were selected. When initial endocardial mapping was not successful for ablation of the pathway, percutaneous transthoracic pericardial puncture was performed via a subxiphoid approach, and an ablation catheter was positioned at the epicardial aspect of the putative AP location for epicardial-endocardial electrogram comparison. Endocardial RF energy was applied to locations considered appropriate. Epicardial RF applications were delivered when endocardial applications failed. Coronary arteriography was performed to assess the proximity of coronary arteries to the ablation catheter., Results: APs were located in the right free wall (4 patients, 5 APs) and the right (1 patient) and left (1 patient) posteroseptal regions. In all patients, epicardial mapping assisted in identifying successful ablation sites. In 3 patients, the earliest atrial activation during orthodromic tachycardia was present in an epicardial electrogram. Successful AP ablation was achieved with an epicardial RF application in 2 patients, either alone or with simultaneous endocardial-epicardial delivery. In the remaining 4 patients, APs were successfully ablated endocardially after epicardial mapping. These patients represent 18% of all cases referred to our institution for ablation of previously failed accessory pathways (6/32 patients)., Conclusions: A combined endocardial-epicardial approach to mapping and RF ablation can facilitate successful endocardial ablation in most cases. In selected cases, APs can be ablated by epicardial delivery of RF. Epicardial mapping is an effective alternative to cardiac surgery for patients in whom prior attempts at AP ablation have failed.