Pericardial anatomy for the interventional electrophysiologist

Long-term pericardial catheterization is associated with minimum foreign-body response

OBJECTIVES

The goals of this study were to assess the feasibility and to characterize the foreign-body response of a long-term catheter in the pericardium.

BACKGROUND

Long-term access to the normal pericardial space provides opportunities for diagnostic sampling and therapeutic intervention.

METHODS

After thoracotomy, in 7 anesthetized canines, the pericardium was opened and a 5 French silicone vascular access catheter was advanced 10 cm into the pericardial sac toward the apex of the heart. A hydraulic coronary balloon occluder was implanted (N=6). Pericardium was sealed with Prolene suture. Catheters were tunneled to the nape of the neck, attached to a subcutaneous vascular access port, and buried in the fascia. Animals underwent multiple experimental coronary artery occlusions across months. At sacrifice, we assessed the histopathological response of pericardium and epicardium to chronically indwelling silicone catheters.

RESULTS

Post-mortem examinations were performed at 213 days post-operatively (mean, range=96-413, N=6), with one animal maintained for longer-term study. At sacrifice, all catheters were bidirectionally patent and completely mobile in the pericardium without evidence of tissue overgrowth around the intrapericardial segment. Adhesion tissue was found only at the site of catheter entry through the pericardium. Microscopic histopathological examination at catheter entry site, surrounding pericardium, and myocardium revealed minimum chronic inflammation.

CONCLUSIONS

This subcutaneous system provides dependable, chronic access to the normal pericardial space for drug delivery and sampling. The presence of a chronic silicone catheter in the pericardium does not precipitate clinically significant pathologic changes even after repeated ischemic events.

Remote Magnetic Navigation to Guide Endocardial and Epicardial Catheter Mapping of Scar-Related Ventricular Tachycardia

BACKGROUND

The present study examines the safety and feasibility of using a remote magnetic navigation system to perform endocardial and epicardial substrate-based mapping and radiofrequency ablation in patients with scar-related ventricular tachycardia (VT).

METHODS AND RESULTS

Using the magnetic navigation system, we performed 27 procedures on 24 consecutive patients with a history of VT related to myocardial infarction, dilated cardiomyopathy, arrhythmogenic right ventricular cardiomyopathy, hypertrophic cardiomyopathy, or sarcoidosis. Electroanatomic mapping of the left ventricular, right ventricular, and ventricular epicardial surfaces was constructed in 24, 10, and 12 patients, respectively. Complete-chamber VT activation maps were created in 4 patients. A total of 77 VTs were inducible, of which 21 were targeted during VT with the remotely navigated radiofrequency ablation catheter alone. With a combination of entrainment and activation mapping, 17 of 21 VTs (81%) were successfully terminated in a mean of 8.4+/-8.2 seconds; for the remainder, irrigated radiofrequency ablation was necessary. The mean fluoroscopy times for endocardial and epicardial mapping were 27+/-23 seconds (range, 0 to 105 seconds) and 18+/-18 seconds (range, 0 to 49 seconds), respectively. In concert with a manually navigated irrigated ablation catheter, 75 of 77 VTs (97%) were ultimately ablated. Four patients underwent a second procedure for recurrent VT, 3 with the magnetic navigation system. After 1.2 procedures per patient, VT did not recur during a mean follow-up of 7+/-3 months (range, 2 to 12 months).

CONCLUSIONS

The present study demonstrates the safety and feasibility of remote catheter navigation to perform substrate mapping of scar-related VT in a wide range of disease states with a minimal amount of fluoroscopy exposure.

Source localization of focal ventricular arrhythmias using linear estimation, correlation, and back propagation networks

Catheter-based approaches used in the localization and treatment of the source of heart rhythm disturbances (arrhythmias) have become popular, because they do not require highly invasive and risky open-chest operations. In most of the existing approaches, mapping of the outer surface (epicardium) is not possible even though arrhythmic substrates involving epicardial and subepicardial layers account for about 15% of the ventricular tachycardias. In this study, we report a feasibility study of a novel mapping approach targeting the epicardium which is based on the measurements of multielectrode catheters placed in the coronary veins. We investigated three methods in determining the most probable region of early activation, i.e., the region that contains the source of the abnormal activation on the heart, using only a set of sparse venous catheter recordings. The methods we proposed here were the linear estimation, correlation, and the back propagation networks. The linear estimation technique hypothesized the relationship between venous catheter measurements and unmeasured epicardial sites based on a previously recorded training data set. The correlation method included a comparative analysis between test and training epicardial activation time maps based on the measured values from the venous sites. In the back propagation method, the input layer consisted of the source data in the form of 42 nodes which were the activation time values from the intravenous catheter leads. We used two hidden layers with 600 and 500 nodes, respectively. The output layer consisted of 28 nodes in the output layer that corresponded to the manually selected early activation regions on the epicardium. The results of the linear estimation and the correlation methods showed that they could be used as a good predictor for the region of early activation, and thus, these approaches may be employed to direct a subsequent more focused electrophysiological study and curative radiofrequency (RF) ablation. The back propagation network approach performed relatively well for the right ventricularly paced beats and the results demonstrated its potential as a supporting technique to the estimation and correlation methods. The results of this study encourage further investigation and provides evidence that an epicardial mapping approach based on the venous catheter recordings is feasible and can provide adequate accuracy for clinical applications.

Substrate-based catheter ablation of epicardial ventricular tachycardia related to an anomalous coronary artery

Delayed enhancement magnetic resonance imaging is known for its ability to identify scarred myocardial tissue. This case report describes the use of MR imaging to define the location and transmural extent of infarcted tissue in a 45-year-old woman with an anomalous right coronary artery and hemodynamically unstable ventricular tachycardia. By demonstrating a predominantly epicardial infarct, MR imaging indicated that the pericardial approach was necessary for successful substrate-based ventricular tachycardia ablation.

Validation of three-dimensional cardiac image integration: use of integrated CT image into electroanatomic mapping system to perform catheter ablation of atrial fibrillation

INTRODUCTION

Accurate visualization of the complex left atrial (LA) anatomy and the location of an ablation catheter within the chamber is important in the success and safety of ablation for atrial fibrillation (AF). We describe the integration of CT into an electroanatomic mapping (EAM) system and its validation in patients undergoing catheter ablation for AF.

METHODS AND RESULTS

Thirty patients (59.2 +/- 8 years, 25 M) with paroxysmal (12) and persistent (18) AF underwent ablation using CT image integration into an electroanatomic mapping system. CT registration using the pulmonary veins as markers (landmark) was achieved with an error of 6.4 +/- 2.8 mm with repeat registration required in two patients. Registration of the CT by best fit to a electroanatomic geometry (surface) was achieved with an error of 2.3 +/- 0.4 mm. There was no significant difference in the regional LA registration error at superior (1.7 +/- 0.7 mm), inferior (2.2 +/- 1.4 mm), septal (1.7 +/- 0.8 mm), and lateral (1.7 +/- 0.7 mm, P = 0.13) sites. Cardiac rhythm at the time of CT did not have a significant effect on total or regional surface registration accuracy (mean total 2.5 +/- 0.3 in AF patients vs 2.3 +/- 0.5 in SR patients, P = 0.22). The integrated CT was used to guide the encirclement of the pulmonary veins (PV) in pairs with electrical isolation achieved by maintaining ablation along the ablation line in 58 of 60 PV pairs. Postprocedural PV angiography did not demonstrate significant stenosis.

CONCLUSION

CT image integration into an EAM system was successfully performed in patients undergoing catheter ablation for AF. With a greater appreciation of the complex and variable nature of the PV and LA anatomy this new technology may improve the efficacy and safety of the procedure.

Mapping epicardial fat with multi-detector computed tomography to facilitate percutaneous transepicardial arrhythmia ablation

A sizable portion of ventricular tachycardia circuits are epicardial, especially in patients with non-ischemic cardiomyopathy, e.g. Chagas disease. Thus there is a growing interest among the electrophysiologists in transepicardial mapping and myocardial ablation for treatment of arrhythmias. However, increased epicardial fat can be a significant hindrance in procedural success as it can mimic infarct during mapping and can also decrease the effectiveness of ablation. Quantitative knowledge of epicardial fat pre-procedure can potentially significantly facilitate the conduct and outcomes of these procedures. In this study we assessed the epicardial fat distribution and thickness in vivo in 59 patients who underwent multi-detector computed tomography (MDCT) for coronary artery assessment using a 16-slice scanner. Multiplanar reconstructions were obtained in the ventricular short axis at the basal, mid ventricular, and near the apex level, and in a four-chamber view. In the short axis slices, we measured epicardial fat diameter in nine segments, and in the four-chamber view, it was measured in five segments. In grooved segments the maximum fat thickness was recorded, while in non-grooved segments thickness at three equally spaced points were averaged. The results were as follows starting clockwise: superior inter-ventricular (IV) groove (all measurements are in mm, in basal, mid ventricular, and apical levels, respectively) (11.2, 8.6, 7.3), left ventricular (LV) superior lateral wall (1.0, 1.5, 1.7), LV inferior lateral wall (1.3, 2.2, 3.5), inferior IV groove (9.2, 6.5, 6.1), right ventricular (RV) diaphragmatic wall (1.4, 0.2, 1.0), acute margin (9.2, 7.3, 7.8), RV anterior free wall inferior (6.8, 4.0, 4.7), RV anterior free wall superior (6.5, 3.2, 3.1), RV superior wall (5.6, 2.7, 4.0), We measured the following four-chamber segments: LV apex (2.8 mm), left atrio-ventricular (AV) groove (12.7), right AV groove (14.8), RV apex (4.8), and anterior IV groove (7.7). The mean epicardial fat thickness for all cases was 5.3 mm (S.D. 1.6). The mean total epicardial fat for patients over 65 was 22% greater than younger patients, with a 36% increase along the RV anterior free wall, 57% along the RV diaphragmatic wall and 38% along the LV lateral wall. Women averaged 17% more total epicardial fat. In conclusion, this study was designed to provide an epicardial fat map for physicians performing percutaneous epicardial mapping and interventions. While the acute margin and RV anterior free wall tend to have high epicardial fat, and the LV lateral wall and RV diaphragmatic wall tend to have little to no fat, there is significant variation between patients. MDCT is a reliable modality for visualizing epicardial fat, and should be considered prior to undergoing procedures that are affected by epicardial fat content, especially in elderly and female populations.

Epicardial Ablation With Cooled Tip Catheter Close to the Coronary Arteries is Effective and Safe in the Porcine Heart if the Ventricular Potential is Being Monitored in the Epicardium and Endocardium

BACKGROUND

Transthoracic epicardial ablation can be an alternative to conventional treatment for critical pathways of ventricular tachycardia located in the epicardium. However, the usefulness and safety of epicardial ablation close to the coronary arteries (CA) is not clear. The purpose of the present experimental animal study was to analyze the efficacy and safety of epicardial radiofrequency (RF) ablation close to the CA.

METHODS AND RESULTS

Of the left ventricle-epicardium ablated sites, 35 lesions (20 with cooling and 15 without cooling) were close to the CA (left anterior descending artery < or = 15 mm) and 33 lesions (23 with cooling and 10 without cooling) were further from the CA. For sites close to the CA, epicardial ablation was effective in 77% (15/20) with cooling and in 40% (6/15) without cooling. There was a significant difference of effective ablation between with cooling and without cooling (p < 0.05). For cooling, epicardial lesion size could be predicted by the change of endocardial ventricular potential using a basket catheter. No damage to major epicardial arteries was detected when the catheter tip was positioned 5 mm away from the CA.

CONCLUSIONS

Close to the CA, RF ablation with cooling is more effective than RF without cooling and is safe if the ablation sites are located 5 mm away from the major CA.

Percutaneous epicardial mapping during ablation of difficult accessory pathways as an alternative to cardiac surgery

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.

Catheter Ablation of Ventricular Epicardial Tissue

Background— Transthoracic epicardial catheter ablation is an emerging catheter ablation strategy being used clinically at increasing frequency. However, the efficacy of standard RF ablation on the epicardial surface of the heart is hindered by (1) the lack of convective cooling of the ablation electrode and (2) the varying presence of epicardial adipose tissue interposed between the ablation electrode and the target site. This experimental animal study examines the biophysical characteristics of radiofrequency (RF) ablation lesions generated by either standard or cooled-tip ablation of the ventricular epicardium.

Methods and Results— Nonsurgical subxyphoid pericardial access was achieved in 10 normal goats and 7 pigs with healed myocardial infarctions. A 4-mm cooled-tip RF ablation catheter (continuous 0.9% saline circulation at 0.6 mL/s; goal temperature, 40°C; 60 seconds) was used to deliver epicardial ventricular lesions: 47 in normal tissue and 22 in infarcted tissue. Standard RF ablation lesions (n=33) using a 4-mm top catheter (goal temperature, 70°C; 60 seconds) were also placed on normal epicardial tissue. Lesions created with standard and cooled-tip RF ablation were 3.7±1.3 mm (25±16.8 W) and 6.7±1.7 mm (44.8±6.8 W) in depth, respectively. On scar tissue, lesions made with the cooled-tip catheter measured 14.6±2.7 mm in length, 11.8±2.9 mm in width, and 5.6±1.2 mm in depth (35.6±7.1 W). In areas covered by epicardial fat (3.1±1.2 mm thick), standard RF energy did not generate any appreciable lesions, but cooled-tip RF lesions were 4.1±2 mm in depth (45±4.4 W).

Conclusions— Cooled-tip RF ablation can generate epicardial lesions more effectively than standard RF ablation and appears to be of particular benefit in ablating areas with overlying epicardial fat.