Efficacy of a cooled bipolar epicardial radiofrequency ablation probe for creating transmural myocardial lesions

The Minimum Number of Ablation Lines for Complete Isolation of the Pulmonary Veins during Thoracoscopic Ablation for Atrial Fibrillation

Total thoracoscopic ablation has been recommended as a class IIa indication for atrial fibrillation. However, the optimal number of ablation lines for pulmonary vein isolation has not yet been proposed. This study aimed to report the minimum number of ablation lines required to achieve an intraoperative conduction block. This study included a total of 20 patients who underwent total thoracoscopic ablation from December 2020 to July 2021. The epicardial conduction block was checked after each ablation line of pulmonary vein antral clamping. The median age was 61 years old. The median duration of atrial fibrillation since the first diagnosis was 78 months. Pulmonary vein isolation with bidirectional conduction block was confirmed in 90% of patients. A median of six ablation lines around each pulmonary vein antrum were performed according to our protocol even after the conduction block was verified. The median number of ablations to achieve an exit block was two on the right side and 3.5 on the left side. We found that most conduction blocks were achieved within three ablations around the pulmonary vein antrum. Our results may provide evidence to reduce the number of unnecessary ablation lines in the future.

Comparison between biparietal bipolar and uniparietal bipolar radio frequency ablation techniques in a simultaneous procedural setting

Purpose

To make an in vitro evaluation of the lesion size and depth produced in two different sets of radio frequency energy bipolar delivery: simultaneous biparietal bipolar (SBB) and simultaneous uniparietal bipolar (SUB).

Methods

Two separate prototypes have been built for our purpose: one to be used in SBB mode and the other to be used SUB mode. Forty left atrium samples were taken from the hearts of freshly slaughtered pigs. They were ablated into a simulator ABLABOX, where blood flow, temperature, and contact force were controlled. After being sliced into a cryotome, the samples were digitalized by a flatbed scanner, and the images were analyzed by a computer morphometric software.

Results

Transmural lesions were achieved in 18/20 samples (90%) in SBB, while SUB showed transmurality in 9/20 samples (45%). Overall maximum diameter (D_MAX) resulted larger in SUB than in SBB (2.43 ± 0.30 mm, 1.62 ± 0.14 mm, respectively; p < 0.05): Moreover, maximum epicardial and endocardial diameters (D_EPI and D_ENDO, respectively) were wider in SUB group than SBB group (2.28 ± 0.30 mm, 2.26 ± 0.40 and 1.60 ± 0.14 mm, 1.59 ± 0.15 mm, respectively; p < 0.05). We observed the same tendency in lesion depth: The total area and volume (A_TOT and V_TOT) were broader in SUB group than in SBB one (581.01 ± 65.38 mm/mm², 58.10 ± 6.53 mm/mm³ and 521.97 ± 73.05 mm/mm², 52.19 ± 7.30 mm/mm³. respectively; p < 0.05).

Conclusions

In contrast with the smaller lesion sizes, the biparietal bipolar group showed a higher transmurality rate. These findings may suggest a better drive of the energy flow when compared with SUB lesions.

Hybrid Surgical Ablation for Ventricular Arrhythmias

Hybrid surgical ventricular tachycardia (VT) ablation combines surgical epicardial access/exposure with contemporary mapping and ablation techniques adapted from percutaneous catheter ablation procedures. Patients considered for a hybrid surgical approach for VT are those who have had prior cardiac surgery or failed percutaneous epicardial access due to pericardial adhesions. They often represent the most challenging end of the spectrum of patients and usually have undergone multiple unsuccessful ablations. In this review, the indications, preprocedure work-up, ablation techniques, and outcomes from hybrid surgical access VT ablations are discussed as well as key technical details that present unique challenges to its success.

The Same is Not the Same: Device Effect during Bipolar Radiofrequency Ablation of Atrial Fibrillation

BACKGROUND

Different ablation devices deliver the same type of energy but use individual control mechanisms to estimate efficacy. We compared patient outcome after the application of radiofrequency ablation systems, using temperature- or resistance-control in paroxysmal and persistent atrial fibrillation (AF).

METHODS

This is an unselected all-comers study. Patients underwent standardized left atrial (paroxysmal atrial fibrillation, [PAF] n = 31) or biatrial ablation (persistent atrial fibrillation [persAF] n = 61) with bipolar RF from October 2010 to June 2013. Patients with left atrial dilatation (up to 57 mm), reduced left ventricular (LV) function, and elderly were included. We used resistance-controlled (RC) or temperature-controlled (TC) devices. We amputated atrial appendices and checked intraoperatively for completeness of pulmonary vein exit block. All patients received implantable loop recorders. Follow-up interval was every 6 months. Antiarrhythmic medical treatment endured up to month 6.

RESULTS

We reached 100% freedom from atrial fibrillation (FAF) in PAF. In perAF 19% of the RC but 82% of the TC patients reached FAF (12 months; p < 0.05). TC patients exhibited higher creatine kinase-muscle/brain (CK-MB) peak values. In persAF, CK-MB-levels correlated to FAF. No and no mortality (30 days) was evident. Twelve-month mortality did not correlate to AF type, AF duration, LV dimension, or function and age. Prolonged need of oral anticoagulants was 90.1% (RC) and 4.5% (TC).

CONCLUSION

In patients with persAF undergoing RF ablation, TC reached higher FAF than RC. Medical devices are not "the same" regarding effectiveness even if used according to manufacturer's instructions. Thus, putative application of "the same" energy is not always "the same" efficacy.

Contact forces during hybrid atrial fibrillation ablation: an in vitro evaluation

PURPOSE

Data on epicardial contact force efficacy in dual epicardial-endocardial atrial fibrillation ablation procedures are lacking. We present an in vitro study on the importance of epicardial and endocardial contact forces during this procedure.

METHODS

The in vitro setup consists of two separate chambers, mimicking the endocardial and epicardial sides of the heart. A circuit, including a pump and a heat exchanger, circulates porcine blood through the endocardial chamber. A septum, with a cut out, allows the placement of a magnetically fixed tissue holder, securing porcine atrial tissue, in the middle of both chambers. Two trocars provide access to the epicardium and endocardium. Force transducers mounted on both catheter holders allow real-time contact force monitoring, while a railing system allows controlled contact force adjustment. We histologically assessed different combinations of epi-endocardial radiofrequency ablation contact forces using porcine atria, evaluating the ablation's diameters, area, and volume.

RESULTS

An epicardial ablation with forces of 100 or 300 g, followed by an endocardial ablation with a force of 20 g did not achieve transmurality. Increasing endocardial forces to 30 and 40 g combined with an epicardial force ranging from 100 to 300 and 500 g led to transmurality with significant increases in lesion's diameters, area, and volumes.

CONCLUSIONS

Increased endocardial contact forces led to larger ablation lesions regardless of standard epicardial pressure forces. In order to gain transmurality in a model of a combined epicardial-endocardial procedure, a minimal endocardial force of 30 g combined with an epicardial force of 100 g is necessary.

Histopathology of Bipolar Radiofrequency Ablation in the Human Atrium

BACKGROUND

The Cox maze IV operation has become the preferred surgical treatment for atrial fibrillation, as it is associated with less morbidity and complexity than the Cox maze III procedure, yet is still highly effective. Numerous studies have been conducted in animals to examine the histopathology of this operation on the heart but studies on human hearts that have undergone the Cox maze IV operation have not been performed.

METHODS

We report the histopathologic findings in 3 patients from whom tissue was available for histologic study. In 2 patients it was obtained at autopsy within a month after undergoing a Cox maze IV operation, and in the remaining patient, atrial tissue was obtained immediately after ablation.

RESULTS

The lesions were clearly visible on the atria at day 6 and day 18. Microscopic examination showed that the hearts were in different stages of healing. We also found that, compared with animal models, human myocardium had significant preexisting underlying damage with myocyte hypertrophy and fibrosis. Although most of the ablative lesions were transmural, not all spanned from the epicardium to the endocardium. The chronic changes present in these hearts may have prevented transmurality by impeding energy delivery from fully penetrating the tissue.

CONCLUSIONS

The atrial myocardial substrate studied in experimental conditions is markedly different from the human hearts that frequently express histopathologic changes secondary to the underlying disease process. That may prevent creating true transmural lesions and impact final efficacy of the procedure.

The surgical treatment for atrial fibrillation: ablation technology and surgical approaches

The Cox maze procedure developed originally in 1987 by Dr James Cox has evolved from a "cut and sew" surgical procedure, where the maze was applied using multiple surgical cuts, to an extensive use of surgical ablation technology where ablation lesions are placed with alternative energy sources (radiofrequency, cryothermy, microwave, and high-frequency ultrasound). Furthermore, the procedure has changed from a median sternotomy approach only to one that can be performed minimally invasively and robotically. The purpose of this paper is to review the current available technology for the ablation of atrial fibrillation as well as the different procedural approaches for the surgical ablation of atrial fibrillation.

Initial experience of sequential surgical epicardial-catheter endocardial ablation for persistent and long-standing persistent atrial fibrillation with long-term follow-up

BACKGROUND

Patients with long-standing persistent (LSP) atrial fibrillation (AF) who have previously undergone catheter ablation represent a challenging patient population. Repeat catheter ablation in these patients is arduous and associated with a high failure rate, whereas surgical ablation can be complicated by multiple flutters. We sought to determine if minimally-invasive surgical ablation, followed by catheter ablation of all inducible flutters, would improve success rates over repeat catheter ablation alone.

METHODS

Fifteen patients (Sequential) with persistent or LSP AF who failed at least one catheter ablation and one anti-arrhythmic drug (AAD) underwent surgical ablation, followed by planned endocardial evaluation and catheter mapping with ablation during the same hospitalization. Sequential patients were matched to 30 patients who had previously failed at least one catheter ablation and underwent a repeat catheter ablation (catheter-alone). The primary end point was event-free survival of any documented AF recurrence or AAD use.

RESULTS

All patients underwent uncomplicated surgical ablation and electrophysiology procedure. Five Sequential patients had seven inducible flutters that were mapped and ablated. After a mean follow-up of 20.7±4.5 months, 13/15 (86.7%) Sequential patients, but only 16/30 (53.3%) catheter-alone patients, were free of any atrial arrhythmia and off of AAD (p=0.04). On AAD, 14/15 (93.3%) Sequential patients were free of any atrial arrhythmia recurrence, compared to 17/30 (56.7%) catheter-alone patients (p=0.01).

CONCLUSIONS

For patients with atrial fibrillation who have failed catheter ablation, Sequential minimally invasive epicardial surgical ablation, followed by endocardial catheter-based ablation, has a higher early success rate than repeat catheter ablation alone.