Atrial fibrillation propagates through gaps in ablation lines: implications for ablative treatment of atrial fibrillation

Surgical treatment of atrial fibrillation in mitral valve surgery: a narrative review

Background and Objective

Atrial fibrillation (AF) is one of the most common arrhythmias in clinical practice, which leads to cardiac decompensation, cardiovascular and cerebrovascular infarction, and other thromboembolic diseases. AF is one of the most common comorbidities of valvular heart disease, especially in mitral valve disease. At the time of their mitral valve surgery, 20-42% of patients have AF. It is beneficial to maintain postoperative sinus rhythm and minimize complications when AF surgery is performed concurrently with mitral valve surgery. This review describes the surgical management of AF in mitral valve surgery, including AF surgical route, surgical ablation technology and surgical approaches. The aim of this review is to enable more patients with AF to receive more appropriate and individualised treatment.

Methods

A narrative review was conducted on the literature on PubMed, Embase including all relevant studies published until November 2023.

Key Content and Findings

This review focuses on the surgical management of AF during mitral valve surgery, including AF surgical route, surgical ablation technology and surgical approaches.

Conclusions

Mitral valve surgery combined with AF surgery facilitates the maintenance of postoperative sinus rhythm in patients, reduces the risk of postoperative stroke, and improves survival. Advances in ablation technology have reduced the difficulty of the procedure, making it possible for more patients to undergo surgical ablation. In the future, it will be possible to tailor specific lesion sets and ablation modalities for individual patients. This would make surgical treatment of AF more effective and applicable to a larger population of patients with AF and mitral valve disease.

Pathophysiology of Atypical Atrial Flutters

Atypical atrial flutters are complex supraventricular arrhythmias that share different pathophysiological aspects in common. In most cases, the arrhythmogenic substrate is essentially embodied by slow-conducting areas eliciting re-entrant circuits. Although atrial scarring seems to promote slow conduction, these arrhythmias may occur even in the absence of structural heart disease. To set out the ablation strategy in this setting, three-dimensional mapping systems have proved invaluable over the last decades, helping the cardiac electrophysiologist understand the electrophysiological complexity of these circuits and easily identify critical areas amenable to effective catheter ablation.

Does left atrial epicardial conduction time reflect atrial fibrosis and the risk of atrial fibrillation recurrence after thoracoscopic ablation? Post hoc analysis of the AFACT trial

OBJECTIVES

To determine the association between left atrial epicardial conduction time (LAECT), fibrosis and atrial fibrillation (AF) recurrence after thoracoscopic surgical ablation of persistent AF.

SETTING

Single tertiary care centre in the Netherlands.

PARTICIPANTS

Patients with persistent AF from the randomised Atrial Fibrillation Ablation and Autonomic Modulation via Thoracoscopic Surgery (AFACT)-trial were included. Patients eligible for thoracoscopic AF ablation were included, full inclusion and exclusion criteria were previously published. All patients underwent thoracoscopic ablation, encompassing pulmonary vein isolation with an additional roof and trigone lesion. In patients with conduction block across the roof and trigone lesion, LAECT was measured. LAECT was defined as the time to local activation at one side of the roofline on pacing from the opposite side. Collagen fibre density was quantified from left atrial appendage histology.

OUTCOME MEASURES

Primary outcome: AF recurrence during 2 years of follow-up.

RESULTS

121 patients were included, of whom 35(29%) were women, age was 60.4±7.8 and 51% (62) had at least one AF recurrence during 2 years of follow-up. LAECT was longer in patients with versus without AF recurrence (182±43 ms vs 147±29 ms, p<0.001). LAECT was longer in older patients, in patients with a higher body mass index (BMI) and in patients using class IC antiarrhythmic drugs. LAECT was shorter in patients with higher collagen fibre density. A previously failed catheter ablation, LAECT and BMI were independently associated with AF recurrence.

CONCLUSION

LAECT is correlated with collagen fibre density and BMI and is independently associated with AF recurrence in patients with persistent AF. In these patients, LAECT appears to reflect substrate characteristics beyond clinical AF type and left atrial volume.

TRIAL REGISTRATION NUMBER

NCT01091389.

Atrial fibrillation in patients with coronary heart disease: current state of the problem

Atrial fibrillation is one of the most common types of cardiac arrhythmia observed in clinical practice. Despite advances in the diagnosis and treatment, atrial fibrillation remains one of the leading causes of cardiovascular mortality and morbidity. In addition, atrial fibrillation is quite often combined with other pathologies of the cardiovascular system and is a marker of an unfavorable outcome. Several previous studies have demonstrated reduced survival in patients with coronary artery disease and atrial fibrillation who have not undergone surgery for arrhythmia. According to other data, the presence of preoperative atrial fibrillation among patients undergoing isolated coronary artery bypass grafting was associated with significantly higher rates of major postoperative complications. Nowadays, no one doubts the fact that atrial fibrillation during a coronary artery bypass surgery is a risk factor for increased hospital mortality, postoperative morbidity and leads to a decrease in the long-term survival. The studies confirm the necessity of surgical ablation for atrial fibrillation during coronary revascularization to reduce both short-term and long-term postoperative mortality and late complications.

Biparietal bidirectional bipolar radiofrequency in hybrid cardiac ablation: an in vitro evaluation

 

OBJECTIVES

The aim of this study was to evaluate the lesion size and depth of radiofrequency (RF) ablation in a simultaneous biparietal bidirectional bipolar (SBB) approach, compared to a simultaneous and staged unipolar and uniparietal bipolar setup [simultaneous uniparietal bipolar (SiUB) and staged uniparietal bipolar (StUB), respectively].

METHODS

Fresh left atrial porcine tissue was mounted into the ABLA-BOX simulator. Different ablation approaches were tested: (i) SBB: a concept consisting of SBB endo-epicardial ablation, (ii) SiUB: simultaneous epicardial uniparietal bipolar and endocardial unipolar ablation and (iii) StUB: staged epicardial uniparietal bipolar and endocardial unipolar ablation. In the StUB setup, a 1-h interval between the epi-endo ablation was respected.

RESULTS

Transmural lesions were present in 90% of the bipolar biparietal ablations, yet no full transmurality was observed in the simultaneous nor in the staged unipolar with uniparietal bipolar ablation group. In SBB, the area and volume of the ablation lesions were smaller (523.33 mm2/mm and 52.33 mm3/mm, respectively) than in SiUB (588.17 mm2/mm and 58.81 mm3/mm, respectively) and StUB (583.76 mm2/mm and 58.37 mm3/mm, P = 0.044). Also, in SBB, the overall, epicardial and endocardial maximum diameters of the lesions (1.59, 1.57 and 1.52 mm; respectively) were smaller than in SiUB (2.38, 2.26 and 2.33 mm; respectively) and in StUB (2.36, 2.28 and 2.14 mm; respectively, all P < 0.001).

CONCLUSIONS

Although bipolar biparietal bidirectional RF ablation results in smaller lesions than uniparietal bipolar and unipolar ablation, their capacity to penetrate the tissue is much higher. Moreover, in uniparietal RF applications, the energy spreads in the superficial layers of the tissue but fails to penetrate. Therefore, the degree of transmurality is much higher when using such a 'truly bipolar' ablation approach.

Isolated left atrial cryoablation of atrial fibrillation in conventional mitral valve surgery

BACKGROUND

Recent trends of surgery for atrial fibrillation (AF) are towards more safe and effective energy sources, as well as to simplified sets of atrial lesions.

METHODS

One hundred eighteen (mean age, 67.4 ± 9.2 years) selected patients with paroxysmal/persistent AF and mitral valve (MV) disease underwent cryoablation of AF combined with conventional (not via mini-thoracotomy) MV surgery; the lesion set was limited to only the left atrium. Multivariable analyses identified predictors of cardiac rhythm at hospital discharge and follow-up.

RESULTS

There were 7 (5.9%) hospital deaths; 33 (28%) patients were discharged on AF. Higher values of preoperative left atrial volume index (odds ratio [OR] = 1.07, 95% confidence interval [95%CI]: 1.01-1.13) and mixed etiology of MV disease (OR = 4.19, 95%CI: 1.23-14.2) were predictors of hospital discharge on AF. Seventy-four (66.7%) patients were on stable sinus rhythm at follow-up (median period, 6.6 years); the 1, 5, and 10-year nonparametric estimates of adjusted freedom from AF were 98.1%, 89.2% and 45.6%, respectively. Higher values of preoperative systolic pulmonary artery pressure (hazard ratio [HR] = HR = 1.04, 95%CI: 1.01-1.08) and AF at hospital discharge (HR = 4.14, 95%CI: 1.50-11.4) were predictors of AF at follow-up.

CONCLUSIONS

During conventional MV surgery, a cryo-lesion set limited to only the left atrium may give good, immediate and long-term results. Left atrial dilation and mixed etiology of MV disease were predictors of hospital discharge on AF. Preoperative pulmonary hypertension and AF at discharge combined with an increased risk of AF at follow-up.

Quantitative evaluation of different high-density 3D mapping modes for atrial and ventricular substrate assessment of cardiac arrhythmias with the HD grid catheter

BACKGROUND

Atrial and ventricular arrhythmias significantly contribute to morbidity and mortality of patients with cardiac disease. Ablation of these arrhythmias has shown to improve clinical outcomes, yet targeted ablation strategies rely on proper mapping capabilities. In the present study, we compare different modes of high-resolution mapping in clinically relevant arrhythmias using HD grid.

METHODS AND RESULTS

Using the Advisor™ HD Grid Mapping Catheter in either the standard, the wave (bipolar along spline and bipolar orthogonal) or the wave diagonal setting, low-voltage areas were determined. Low-voltage was defined as local electrograms with an amplitude <0.5 mV (bipolar; atria/ventricle) or <4 mV (unipolar; ventricle). Ultra high-density mapping in 47 patients with ventricular tachycardia, ventricular premature beats, atrial fibrillation and atrial tachycardia provided reliable information for the understanding of the arrhythmia mechanism resulting in safe ablation procedures. Regions of low voltage were significantly decreased by 14 ± 2% and 31 ± 3% with wave and wave diagonal settings as compared to standard settings, respectively.

CONCLUSION

Substrate mapping and risk stratification relies on proper low voltage discrimination. Even though the Advisor™ HD Grid Mapping Catheter was safely used in all cases, the extent of low voltage areas was mapping-mode dependent.

Catheter Ablation Lesion Visualization With Intracardiac Strain Imaging in Canines and Humans

Catheter ablation is a common treatment for arrhythmia, but can fail if lesion lines are noncontiguous. Identification of gaps and nontransmural lesions can reduce the likelihood of treatment failure and recurrent arrhythmia. Intracardiac myocardial elastography (IME) is a strain imaging technique that provides visualization of the lesion line. Estimation of lesion size and gap resolution were evaluated in an open-chest canine model ( n = 3 ), and clinical feasibility was investigated in patients undergoing ablation to treat typical cavotricuspid isthmus (CTI) atrial flutter ( n = 5 ). A lesion line consisting of three lesions and two gaps was generated on the canine left ventricle via epicardial ablation. One lesion was generated in one canine right ventricle. Average lesion and gap areas were measured with high agreement (33 ± 14 and 30 ± 15 mm², respectively) when compared against gross pathology (34 ± 19 and 26 ± 11 mm², respectively). Gaps as small as 11 mm² (3.6 mm on epicardial surface) were identifiable. Absolute error and relative error in estimated lesion area were 9.3 ± 8.4 mm² and 31% ± 34%; error in estimated gap area was 11 ± 9.0 mm² and 40% ± 29%. Flutter patients were imaged throughout the procedure. Strain was shown to be capable of differentiating between baseline and after ablation completion as confirmed by conduction block. In all patients, strain decreased in the CTI after ablation (mean paired difference of -17% ± 11%, ). IME could potentially become a useful ablation monitoring tool in health facilities.

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.

The influence of epicardial and endocardial use of cryoenergy on the completeness of lesions in surgical ablation of atrial fibrillation

Introduction

Cryoenergy is the most commonly used method of lesion formation in patients who have undergone surgical ablation of atrial fibrillation. Despite frequent use, the clinical effect of cryoenergy in endocardial and epicardial approaches is unknown.

Aim

To compare the effect of various cryoenergy applications on the postoperative incidence of sinus rhythm and completeness of lesions performed.

Material and methods

A total of 55 patients underwent concomitant atrial fibrillation surgical ablation using cryoenergy under various conditions: epicardially during cardiac arrest, epicardially on beating heart, and endocardially. In the postoperative period, patients were invited to attend an electrophysiological examination to assess the completeness of surgical ablation lesions and, if necessary, to complete catheter ablation.

Results

Twenty-four patients underwent epicardial ablation on the arrested heart (group 1), 12 patients underwent epicardial ablation on the beating heart (group 2), and 19 patients underwent endocardial ablation (group 3). In the electrophysiological examination, sinus rhythm was present in 71% vs. 83% vs. 89% of patients, respectively. The completeness of pulmonary vein isolation was confirmed in 31% vs. 25% vs. 95% of patients, complete box lesions in 15% vs. 0% vs. 79% of patients, respectively.

Conclusions

Despite the similar clinical effect of surgical ablation in all three approaches, the morphologically most effective use of cryoenergy is endocardial ablation. This approach has a very good result. Our findings further support the endocardial use of cryoenergy during surgical ablation of atrial fibrillation.

Bipolar Radiofrequency Ablation on Explanted Human Hearts: How to Ensure Transmural Lesions

BACKGROUND

Bipolar radiofrequency (RF) clamps have been shown to be capable of reproducibly creating transmural lesions with a single ablation in animal models. Unfortunately in clinical experience the bipolar clamps have not been as effective and often require multiple ablations to create conduction block. This study created a new experimental model using fresh, cardioplegically arrested human hearts turned down for transplant to evaluate the performance of a nonirrigated bipolar RF clamp.

METHODS

Nine human hearts turned down for transplant were harvested, and the Cox-Maze IV lesion set was performed with a nonirrigated bipolar RF clamp. In the first 7 hearts a single ablation was performed for each lesion. In the last 2 hearts a set of 2 successive ablations without unclamping were performed. The heart tissue was stained with 2,3,5-triphenyl-tetrazolium chloride. Each ablation lesion was cross-sectioned to assess lesion depth and transmurality.

RESULTS

A single ablation with the bipolar RF clamp resulted in 89% (469/529) of the histologic sections and 65% (42/65) of the lesions being transmural. Of the nontransmural sections, 92% occurred in areas with epicardial fat. Performing 2 successive ablations without unclamping resulted in 100% of the cross-sections (201/201) and lesions (25/25) being transmural.

CONCLUSIONS

A single ablation failed to create a transmural lesion 35% of the time, and this was associated with the presence of epicardial fat. Two successive ablations without unclamping resulted in 100% lesion transmurality using the bipolar RF clamp.

Differences between gap-related persistent conduction and carina-related persistent conduction during radiofrequency pulmonary vein isolation

BACKGROUND

During pulmonary vein isolation (PVI), nonisolation after initial encircling of the pulmonary veins (PVs) may be due to gaps in the initial ablation line, or alternatively, earliest PV activation may occur on the intervenous carina and ablation within the wide-area circumferential ablation (WACA) circle is needed to eliminate residual conduction. This study investigated prognostic implications and predictors of gap-related persistent conduction (gap-RPC) and carina-related persistent conduction (carina-RPC) during PVI.

METHODS AND RESULTS

Two hundred fourteen atrial fibrillation (AF) patients (57% paroxysmal, 61% male, mean age 62 ± 9 years) undergoing first contact force-guided radiofrequency PVI were studied. Preprocedural cardiac computed tomography imaging was used to assess left atrial and PV anatomy. PVI was assessed directly after initial WACA circle creation, after a minimum waiting period of 30 minutes, and after adenosine infusion. Persistent conduction was targeted for additional ablation and classified as gap-RPC or carina-RPC, depending on the earliest activation site. The 1-year AF recurrence rate was higher in patients with gap-RPC (47%) compared to patients without gap-RPC (28%; P = .003). No significant difference in 1-year recurrence rate was found between patients with carina-RPC (37%) and patients without carina-RPC (31%; P = .379). Multivariate analyses identified paroxysmal AF and WACA circumference as independent predictors of gap-RPC, whereas carina width and WACA circumference correlated with carina-RPC.

CONCLUSIONS

Gap-RPC is associated with increased AF recurrence risk after PVI, whereas carina-RPC does not predict AF recurrence. Moreover, gap-RPC and carina-RPC have different correlates and may thus have different underlying mechanisms.

Energy Sources for the Surgical Treatment of Atrial Fibrillation

The surgical treatment of atrial fibrillation has evolved over the past 2 decades due to the advent of ablation technology, and the introduction of less invasive surgical approaches. Current devices produce ablation lines that aim to replace the incisions of traditional surgical ablation strategies, such as the Cox-Maze procedure. This has helped to simplify and shorten surgical ablation procedures and has allowed for the development of minimally invasive surgical techniques. This review discusses surgical ablation energy sources and devices, providing background on device characteristics, mechanism of tissue injury, and success in creating transmural lesions.

Management of Atrial Fibrillation in Patients Undergoing Coronary Artery Bypass Grafting: Review of the Literature

Untreated atrial fibrillation is associated with an increased risk of all-cause mortality and morbidity. Despite the current guidelines recommending surgical ablation of atrial fibrillation at the time of coronary artery bypass surgery, most patients with concomitant atrial fibrillation and coronary artery disease do not receive surgical ablation for their atrial fibrillation. This review reports the efficacy of different surgical ablation techniques used for the treatment of atrial fibrillation during coronary artery bypass. PubMed was systematically searched for studies reporting outcomes of concomitant surgical ablation in coronary artery bypass patients between January 2002 and March 2018. Data were independently extracted and analyzed by two investigators. Twenty-four studies were included. Twelve studies exclusively reported outcomes of surgical ablation in patients undergoing coronary artery bypass, whereas the remaining 12 reported outcomes of concomitant cardiac surgery with subgroup analysis. Only four studies performed the concomitant Cox-Maze procedure. Freedom from atrial tachyarrhythmia was reported as high as 98% at 1 year and 76% at 5 years with Cox-Maze procedure, whereas lesser lesion sets had more variable outcomes, ranging from 35% to 93%. In most studies, the addition of surgical ablation was not associated with increased morbidity and mortality. Although the Cox-Maze procedure had the greatest short- and long-term success rates, most studies comprising the evidence documenting the safety and efficacy of adding surgical ablation were of low or moderate quality. There was a great deal of heterogeneity among study populations, follow-up times, methods, and definition of failure. To establish a consensus regarding a surgical ablation technique for atrial fibrillation in coronary artery bypass population, larger multicenter randomized controlled studies need to be designed.

Amaze: a double-blind, multicentre randomised controlled trial to investigate the clinical effectiveness and cost-effectiveness of adding an ablation device-based maze procedure as an adjunct to routine cardiac surgery for patients with pre-existing atrial fibrillation

BACKGROUND

Atrial fibrillation (AF) can be treated using a maze procedure during planned cardiac surgery, but the effect on clinical patient outcomes, and the cost-effectiveness compared with surgery alone, are uncertain.

OBJECTIVES

To determine whether or not the maze procedure is safe, improves clinical and patient outcomes and is cost-effective for the NHS in patients with AF.

DESIGN

Multicentre, Phase III, pragmatic, double-blind, parallel-arm randomised controlled trial. Patients were randomised on a 1 : 1 basis using random permuted blocks, stratified for surgeon and planned procedure.

SETTING

Eleven acute NHS specialist cardiac surgical centres.

PARTICIPANTS

Patients aged ≥ 18 years, scheduled for elective or in-house urgent cardiac surgery, with a documented history (> 3 months) of AF.

INTERVENTIONS

Routine cardiac surgery with or without an adjunct maze procedure administered by an AF ablation device.

MAIN OUTCOME MEASURES

The primary outcomes were return to sinus rhythm (SR) at 12 months and quality-adjusted life-years (QALYs) over 2 years after randomisation. Secondary outcomes included return to SR at 2 years, overall and stroke-free survival, drug use, quality of life (QoL), cost-effectiveness and safety.

RESULTS

Between 25 February 2009 and 6 March 2014, 352 patients were randomised to the control (n = 176) or experimental (n = 176) arms. The odds ratio (OR) for return to SR at 12 months was 2.06 [95% confidence interval (CI) 1.20 to 3.54; p = 0.0091]. The mean difference (95% CI) in QALYs at 2 years between the two trial arms (maze/control) was -0.025 (95% CI 0.129 to 0.078; p = 0.6319). The OR for SR at 2 years was 3.24 (95% CI 1.76 to 5.96). The number of patients requiring anticoagulant drug use was significantly lower in the maze arm from 6 months after the procedure. There were no significant differences between the two arms in operative or overall survival, stroke-free survival, need for cardioversion or permanent pacemaker implants, New York Heart Association Functional Classification (for heart failure), EuroQol-5 Dimensions, three-level version score and Short Form questionnaire-36 items score at any time point. Sixty per cent of patients in each trial arm had a serious adverse event (p = 1.000); most events were mild, but 71 patients (42.5%) in the maze arm and 84 patients (45.5%) in the control arm had moderately severe events; 31 patients (18.6%) in the maze arm and 38 patients (20.5%) in the control arm had severe events. The mean additional cost of the maze procedure was £3533 (95% CI £1321 to £5746); the mean difference in QALYs was -0.022 (95% CI -0.1231 to 0.0791). The maze procedure was not cost-effective at £30,000 per QALY over 2 years in any analysis. In a small substudy, the active left atrial ejection fraction was smaller than that of the control patients (mean difference of -8.03, 95% CI -12.43 to -3.62), but within the predefined clinically equivalent range.

LIMITATIONS

Low recruitment, early release of trial summaries and intermittent resource-use collection may have introduced bias and imprecise estimates.

CONCLUSIONS

Ablation can be practised safely in routine NHS cardiac surgical settings and increases return to SR rates, but not survival or QoL up to 2 years after surgery. Lower anticoagulant drug use and recovery of left atrial function support anticoagulant drug withdrawal provided that good atrial function is confirmed.

FURTHER WORK

Continued follow-up and long-term clinical effectiveness and cost-effectiveness analysis. Comparison of ablation methods.

TRIAL REGISTRATION

Current Controlled Trials ISRCTN82731440.

FUNDING

This project was funded by the NIHR Health Technology Assessment programme and will be published in full in Health Technology Assessment; Vol. 22, No. 19. See the NIHR Journals Library website for further project information.

Predictive risk factors for recurrent atrial fibrillation after modified endoscopic ablation: A 2-year follow-up

BACKGROUND

Our previous study reported a modified endoscopic procedure for nonvalvular atrial fibrillation (AF) that requires only 3 ports in the left chest wall.

HYPOTHESIS

Certain preoperative variables might be predictive risk factors for AF recurrence among patients who underwent this procedure.

METHODS

From October 2010 to April 2014, 114 patients with either paroxysmal AF (PAF) or nonparoxysmal AF (non-PAF) underwent the procedure and completed postoperative cardiac-rhythm measurement via electrocardiography and Holter monitoring. Univariate and multivariate analyses of the possible AF-related risk factors were conducted.

RESULTS

During 2-year follow-up, 99 of 114 patients (86.8%) were free from atrial tachyarrhythmia. Results from univariate analyses showed that AF duration, left atrial diameter (LAD), left atrial minimum volume, left atrial empty fraction, left atrial expansion index, and left atrial active empty fraction (LAAEF) were significantly associated with postoperative AF recurrence. Results from multivariate analyses showed that AF duration (odds ratio [OR]: 1.194, 95% CI: 1.063-1.340, P = 0.003), LAD (OR: 1.101, 95% CI: 1.005-1.205, P = 0.039), and LAAEF (OR: 0.490, 95% CI: 0.277-0.865, P = 0.014) were independent risk factors. There was no difference in AF recurrence between patients with PAF and non-PAF (P = 0.250).

CONCLUSIONS

Our 2-year follow-up study suggested that low LAAEF, long AF duration, and large LAD might be potential predictive risk factors for AF recurrence. Patients with PAF and non-PAF had a similar AF recurrence rate after modified endoscopic ablation.

Right minithoracotomy versus conventional median sternotomy for patients undergoing mitral valve surgery and Cox-maze IV ablation with entirely bipolar radiofrequency clamp

Cox-maze IV ablation by bipolar radiofrequency clamp was considered to be only performed through median sternotomy (MS), but impossible through right minithoracotomy (RM). Now, we developed a novel technique of performing Cox-maze IV ablation entirely by bipolar clamp through RM. To compare the outcomes of RM or MS for patients undergoing mitral valve surgery and concomitant Cox-maze IV ablation with entirely bipolar clamp. All 152 patients underwent mitral valve surgery and concomitant Cox-maze IV ablation with bipolar clamp through RM (n = 69) or MS (n = 83) were analyzed for outcome differences. The etiology of mitral valve disease was rheumatic (n = 97) and degenerative (n = 55). All patients had long-standing persistent atrial fibrillation (AF). Diameter of left atrium ranged from 42 to 60 mm. All patients successfully underwent Cox-maze IV ablation by bipolar clamp. RM group had longer cardiopulmonary bypass time (130.3 ± 17.7 vs 115.3 ± 14.4 min; P < 0.001) and aortic cross-clamp time (91.8 ± 12.7 vs 74.6 ± 9.3 min; P < 0.001). But mechanical ventilation time (14.2 ± 6.6 vs 21.3 ± 9.0 h; P < 0.001) and hospital length of stay (9.3 ± 2.6 vs 11.7 ± 3.0 days; P < 0.001) were shorter in RM group. At discharge, the maintenance of normal sinus rhythm (NSR) was 94.2% in RM group and 95.1% in MS group (P = 1.000). Cumulative maintenance of NSR at 2 years postoperatively was 85.1 ± 5.8% in RM group and 88.6 ± 3.6% in MS group (P = 0.767). RM can achieve similar therapeutic effect to MS for patients undergoing mitral valve surgery and concomitant Cox-maze IV ablation with entirely bipolar clamp. In addition, patients through RM had faster recovery.

Cardiac Lesion Mapping In Vivo Using Intracardiac Myocardial Elastography

Radio frequency (RF) ablation of the myocardium is used to treat various cardiac arrhythmias. The size, spacing, and transmurality of lesions have been shown to affect the success of the ablation procedure; however, there is currently no method to directly image the size and formation of ablation lesions in real time. Intracardiac myocardial elastography (ME) has been previously used to image the decrease in cardiac strain during systole in the ablated region as a result of the lesion formation. However, the feasibility of imaging multiple lesions and identifying the presence of gaps between lesions has not yet been investigated. In this paper, RF ablation lesions ( ) were generated in the left ventricular epicardium in three anesthetized canines. Two sets of two lesions each were created in close proximity to one another with small gaps (1.5 and 4 cm), while one set of two lesions was created directly next to each other with no gap. A clinical intracardiac echocardiography system was programmed to transmit a custom diverging beam sequence at 600 Hz and used to image the ablation site before and after the induction of ablation lesions. Cumulative strains were estimated over systole using a normalized cross-correlational displacement algorithm and a least-squares strain kernel. Afterward, lesions were excised and subjected to tetrazolium chloride staining. Results indicate that intracardiac ME was capable of imaging the reduction in systolic strain associated with the formation of an ablation lesion. Furthermore, lesion sets containing gaps were able to be distinguished from lesion sets created with no gaps. These results indicate that the end-systolic strain measured using intracardiac ME may be used to image the formation of lesions induced during an RF ablation procedure, in order to provide critical assessment of lesion viability during the interventional procedure.

Hyperspectral imaging for label-free in vivo identification of myocardial scars and sites of radiofrequency ablation lesions

BACKGROUND

Treatment of cardiac arrhythmias often involves ablating viable muscle tissue within or near islands of scarred myocardium. Yet, today there are limited means by which the boundaries of such scars can be visualized during surgery and distinguished from the sites of acute injury caused by radiofrequency (RF) ablation.

OBJECTIVE

We sought to explore a hyperspectral imaging (HSI) methodology to delineate and distinguish scar tissue from tissue injury caused by RF ablation.

METHODS

RF ablation of the ventricular surface of live rats that underwent thoracotomy was followed by a 2-month animal recovery period. During a second surgery, new RF lesions were placed next to the scarred tissue from the previous ablation procedure. The myocardial infarction model was used as an alternative way to create scar tissue.

RESULTS

Excitation-emission matrices acquired from the sites of RF lesions, scar region, and the surrounding unablated tissue revealed multiple spectral changes. These findings justified HSI of the heart surface using illumination with 365 nm UV light while acquiring spectral images within the visible range. Autofluorescence-based HSI enabled to distinguish sites of RF lesions from scar or unablated myocardium in open-chest rats. A pilot version of a percutaneous HSI catheter was used to demonstrate the feasibility of RF lesion visualization in atrial tissue of live pigs.

CONCLUSION

HSI based on changes in tissue autofluorescence is a highly effective tool for revealing-in vivo and with high spatial resolution-surface boundaries of myocardial scar and discriminating it from areas of acute necrosis caused by RF ablation.

Anatomical and Optical Properties of Atrial Tissue: Search for a Suitable Animal Model

The purpose of this study was to evaluate structural and optical properties of atrial tissue from common animal models and to compare it with human atria. We aimed to do this in a format that will be useful for development of better ablation tools and/or new means for visualizing atrial lesions. Human atrial tissue from clinically relevant age group was compared and contrasted with atrial tissue of large animal models commonly available for research purposes. These included pigs, sheep, dogs and cows. The presented data include area measurements of smooth atrial surface available for ablation and estimates of thickness of collagen and muscle for five different species. We also described methods to quantify presence of collagen and overall thickness of atrial wall. Provided information enables placement of atrial lesions to locations with clinically relevant atrial wall thickness and macroscopic structure ultimately helping investigators to develop better ablation and imaging tools. It also highlights the impact of collagen thickness on optical measurements and lesion visualization.

Scanned 3-D Intracardiac ARFI and SWEI for Imaging Radio-Frequency Ablation Lesions

Radio-frequency ablation (RFA) is used to locally disrupt electrical propagation in myocardium and treat arrhythmias, and direct visualization of ablation lesions by acoustic radiation force methods may benefit RFA procedures. This paper compares four imaging modalities, B-mode, acoustic radiation force impulse (ARFI), single-track-location shear wave elasticity imaging (STL-SWEI), and multiple-track-location shear wave elasticity imaging (MTL-SWEI), in their ability to resolve RFA lesions in four ex vivo experiments. Ablation lesions are shown to be marked by at least a local halving of ARFI displacements and doubling of shear wave speeds. In a controlled ablation of ex vivo porcine and canine cardiac tissue, STL-SWEI and ARFI are shown to have a similar CNR, better than MTL-SWEI and B-mode. The SWEI modalities are demonstrated to have improved imaging of distal lesion boundaries. Gaps smaller than 5 mm are visualized in ablation lines made of discretely spaced ablations, and complex structures are reconstructed through depth in an "x" ablation experiment. Scans of suspended atria show increased noise, but successfully visualize ablations in ARFI, MTL-SWEI, and STL-SWEI.

Laser applications in surgery

In modern medicine, lasers are increasingly utilized for treatment of a variety of pathologies as interest in less invasive treatment modalities intensifies. The physics behind lasers allows the same basic principles to be applied to a multitude of tissue types using slight modifications of the system. Multiple laser systems have been studied within each field of medicine. The term "laser" was combined with "surgery," "ablation," "lithotripsy," "cancer treatment," "tumor ablation," "dermatology," "skin rejuvenation," "lipolysis," "cardiology," "atrial fibrillation (AF)," and "epilepsy" during separate searches in the PubMed database. Original articles that studied the application of laser energy for these conditions were reviewed and included. A review of laser therapy is presented. Laser energy can be safely and effectively used for lithotripsy, for the treatment of various types of cancer, for a multitude of cosmetic and reconstructive procedures, and for the ablation of abnormal conductive pathways. For each of these conditions, management with lasers is comparable to, and potentially superior to, management with more traditional methods.

Electrophysiological Perspectives on Hybrid Ablation of Atrial Fibrillation

To overcome limitations of minimally invasive surgical ablation as a standalone procedure in eliminating atrial fibrillation (AF), hybrid approaches incorporating adjunctive endovascular catheter ablation have been proposed in recent years. The endovascular component targets residual conduction gaps and identifies additional electrophysiological targets with the goal of minimizing recurrent atrial arrhythmia. We performed a systematic review of published studies of hybrid AF ablation, analyzing 432 pooled patients (19% paroxysmal, 29% persistent, 52% long-standing persistent) treated using three different approaches: A. bilateral thoracoscopy with bipolar radiofrequency (RF) clamp-based approach; B. right thoracoscopic suction monopolar RF catheter-based approach; and C. subxiphoid posterior pericardioscopic ("convergent") approach. Freedom from recurrence off antiarrhythmic medications at 12 months was seen in 88.1% [133/151] for A, 73.4% [47/64] for B, and 59.3% [80/135] for C, with no significant difference between paroxysmal (76.9%) and persistent/long-standing persistent AF (73.4%). Death and major surgical complications were reported in 8.5% with A, 0% with B and 8.6% with C. A critical appraisal of hybrid ablation is presented, drawing from experiences and insights published over the years on catheter ablation of AF, with a discussion of the rationale underlying hybrid ablation, its strengths and limitations, where it may have a unique role in clinical management of patients with AF, which questions remain unanswered and areas for further investigation.

Intracardiac myocardial elastography in canines and humans in vivo

Intracardiac echocardiography (ICE) is a useful imaging modality which is used during RF ablation procedures to identify anatomical structures. Utilizing ICE in conjunction with myocardial elastography (ME) can provide additional information on the mechanical properties of cardiac tissue and provide information on mechanical changes caused by ablation. The objective of this study was to demonstrate that ICE can be used at high frame rate using a diverging beam transmit sequence to image myocardial strain and differentiate myocardial tissue properties before, during, and after ablation for a clinical ablation procedure. In this feasibility study, three normal canines and eight patients with atrial fibrillation (AF) were studied in vivo. A 5.8-MHz ICE transducer was used to image the heart with a diverging beam transmit method achieving 1200 frames per second (fps). Cumulative axial displacement estimation was performed using 1-D cross-correlation with a window size of 2.7 mm and 95% overlap. Axial cumulative strains were estimated in the left atrium (LA) and right atrium (RA) using a least-squares estimator with a kernel of 2 mm on the axial displacements. In the canine case, radial thickening was detected in the lateral wall and in the interatrial septum during LA emptying. For AF patients, the mean absolute strain in the ablated region was lower (6.7 ± 3.1%) than before the ablation (17.4 ± 9.3%) in LA at the end of the LA emptying phase. In the cavotricuspid isthmus (CTI) region, mean absolute strain magnitude at the end of the RA emptying phase was found to be higher during ablation (43.0 ± 18.1%) compared with after ablation (33.7 ± 15.8%). Myocardial strains in the LA of an AF patient were approximately 2.6 times lower in the ablated region than before ablation. This initial feasibility indicates that ME can be used as a new imaging modality in conjunction with ICE in RF ablation guidance and lesion monitoring.

Performance of a novel bipolar/monopolar radiofrequency ablation device on the beating heart in an acute porcine model

OBJECTIVE

Although the advent of ablation technology has simplified and shortened surgery for atrial fibrillation, only bipolar clamps have reliably been able to create transmural lesions on the beating heart. Currently, there are no devices capable of reproducibly creating the long linear lesions in the right and left atria needed to perform a Cox-Maze procedure. This study evaluated the performance of a novel suction-assisted radiofrequency device that uses both bipolar and monopolar energy to create lesions from an epicardial approach on the beating heart.

METHODS

Six domestic pigs underwent median sternotomy. A dual bipolar/monopolar radiofrequency ablation device was used to create epicardial linear lesions on the superior and inferior vena cavae, the right and left atrial free walls, and the right and left atrial appendages. The heart was stained with 2,3,5-triphenyl-tetrazolium chloride, and each lesion was cross-sectioned at 5-mm intervals. Lesion depth and transmurality were determined.

RESULTS

Transmurality was documented in 94% of all cross sections, and 68% of all ablation lines were transmural along their entire length. Tissue thickness was not different between the transmural and nontransmural cross sections (3.1 ± 1.3 and 3.4 ± 2.1, P = 0.57, respectively), nor was the anatomic location on the heart (P = 0.45 for the distribution). Of the cross sections located at the end of the ablation line, 11% (8/75) were found to be nontransmural, whereas only 4% (8/195) of the cross sections located within the line of ablation were found to be nontransmural (P = 0.04). Logistic regression analysis demonstrated that failure of the device to create transmural lesions was associated with low body temperature (P = 0.006) but not with cardiac output (P = 0.54).

CONCLUSIONS

This novel device was able to consistently create transmural epicardial lesions on the beating heart, regardless of anatomic location, cardiac output, or tissue thickness. The performance of this device was improved over most devices previously tested but still falls short of ideal clinical performance. Transmurality was lower at the end of the lesions, highlighting the importance of overlapping lines of ablation in the clinical setting.

Ablation technology for the surgical treatment of atrial fibrillation

The Cox maze procedure for the surgical treatment of atrial fibrillation has been simplified from its original cut-and-sew technique. Various energy sources now exist which create linear lines of ablation that can be used to replace the original incisions, greatly facilitating the surgical approach. This review article describes the anatomy of the atria that must be considered in choosing a successful energy source. Furthermore the device characteristics, safety profile, mechanism of tissue injury, and ability to create transmural lesions of the various energy sources that have been used in the Cox maze procedure, along with the strengths and weaknesses of each device is discussed.

Illustrated techniques for performing the Cox-Maze IV procedure through a right mini-thoracotomy

The Cox-Maze IV procedure has replaced the "cut-and-sew" technique of the original Cox-Maze operation with lines of ablation created using bipolar radiofrequency (RF) and cryothermal energy devices. In select patients, this procedure can be performed through a right mini-thoracotomy. This illustrated review is the first to detail the complete steps of the Cox-Maze IV procedure performed through a right mini-thoracotomy with careful attention paid to operative anatomy and advice. Pre- and post-operative management and outcomes are also discussed. This should be a practical guide for the practicing cardiac surgeon.

The problem with concomitant atrial fibrillation in non-mitral valve surgery

Treatment of atrial fibrillation (AF) in concomitant surgery is not unanimously agreed upon in the cardiac surgical community. The reason for this lack of consensus is threefold. Firstly, there is an absence of large multicenter randomized controlled trials (RCT) proving the benefit of restoring sinus rhythm in a patient population which we encounter almost daily (about 10% of cardiac surgery patients are diagnosed with AF). Secondly, for patients undergoing cardiac surgery without the need for an atriotomy, the Maze procedure is not widely accepted. In these patients, many surgeons do not think that the increased complexity outweighs the potential future benefits of sinus rhythm. Thirdly, due to our limited understanding of this pathology, we are confronted with many choices of ablation tools and lesion sets. In this perspective these issues are reviewed. As a possible solution, a total epicardial lesion set without any incisions is proposed.

Transmural ultrasound imaging of thermal lesion and action potential changes in perfused canine cardiac wedge preparations by high intensity focused ultrasound ablation

Intra-procedural imaging is important for guiding cardiac arrhythmia ablation. It is difficult to obtain intra-procedural correlation of thermal lesion formation with action potential (AP) changes in the transmural plane during ablation. This study tested parametric ultrasound imaging for transmural imaging of lesion and AP changes in high intensity focused ultrasound (HIFU) ablation using coronary perfused canine ventricular wedge preparations (n = 13). The preparations were paced from epi/endocardial surfaces and subjected to HIFU application (3.5 MHz, 11 Hz pulse-repetition-frequency, 70% duty cycle, duration 4 s, 3500 W/cm²), during which simultaneous optical mapping (1 kframes/s) using di-4-ANEPPS and ultrasound imaging (30 MHz) of the same transmural surface of the wedge were performed. Spatiotemporally correlated AP measurements and ultrasound imaging allowed quantification of the reduction of AP amplitude (APA), shortening of AP duration at 50% repolarization, AP triangulation, decrease of optical AP rise, and change of conduction velocity along tissue depth direction within and surrounding HIFU lesions. The threshold of irreversible change in APA correlating to lesions was determined to be 43±1% with a receiver operating characteristic (ROC) area under curve (AUC) of 0.96±0.01 (n = 13). Ultrasound imaging parameters such as integrated backscatter, Rayleigh (α) and log-normal (σ) parameters, cumulative extrema of σ were tested, with the cumulative extrema of σ performing the best in detecting lesion (ROC AUC 0.89±0.01, n = 13) and change of APA (ROC AUC 0.79±0.03, n = 13). In conclusion, characteristic tissue and AP changes in HIFU ablation were identified and spatiotemporally correlated using optical mapping and ultrasound imaging. Parametric ultrasound imaging using cumulative extrema of σ can detect HIFU lesion and APA reduction.

The CURE-AF trial: a prospective, multicenter trial of irrigated radiofrequency ablation for the treatment of persistent atrial fibrillation during concomitant cardiac surgery

BACKGROUND

Ablation technology has been introduced to replace the surgical incisions of the Cox-Maze procedure in order to simplify the operation. However, the efficacy of these ablation devices has not been prospectively evaluated.

OBJECTIVE

The purpose of this study was to examine the efficacy and safety of irrigated unipolar and bipolar radiofrequency ablation for the treatment of persistent and long-standing persistent atrial fibrillation (AF) during concomitant cardiac surgical procedures.

METHODS

Between May 2007 and July 2011, 150 consecutive patients were enrolled at 15 U.S. centers. Patients were followed for 6 to 9 months, at which time a 24-hour Holter recording and echocardiogram were obtained. Recurrent AF was defined as any atrial tachyarrhythmia (ATA) lasting over 30 seconds on the Holter monitor. The safety end-point was the percent of patients who suffered a major adverse event within 30 days of surgery. All patients underwent a biatrial Cox-Maze lesion set.

RESULTS

Operative mortality was 4%, and there were 4 (3%) 30-day major adverse events. Overall freedom from ATAs was 66%, with 53% of patients free from ATAs and also off antiarrhythmic drugs at 6 to 9 months. Increased left atrial diameter, shorter total ablation time, and an increasing number of concomitant procedures were associated with recurrent AF (P <.05).

CONCLUSION

Irrigated radiofrequency ablation for treatment of AF during cardiac surgery was associated with a low complication rate. No device-related complications occurred. The Cox-Maze lesion set was effective at restoring sinus rhythm and had higher success rates in patients with smaller left atrial diameters and longer ablation times.

Double Potential Mapping: A Novel Technique for Locating the Site of Incomplete Ablation

Objective

Double potential mapping using bipolar electrodes that straddle the ablation line should identify the site of incomplete ablation as a conduction gap without constructing the activation maps.

Methods

Bipolar electrograms were recorded during pacing using 11 custom-made bipolar electrodes straddling the ablation line created by a bipolar radiofrequency ablation device on the lateral right atrium in seven canines. A linear ablation was made with an ablation device, of which one jaw was inserted into the atrium through a purse-string suture. A 3-mm-wide tape was placed on both jaws 10 mm from the tip of the ablation electrode to intentionally create an incomplete ablation lesion. The activation times at each dipole across the ablation line were defined as the times of the maximum positive and negative derivatives of the double potentials, and the site of conduction gap was determined as the site of the earliest activation across the linear ablation. The lateral right atrium was mapped simultaneously with 45 different bipolar electrodes to construct the activation maps and the earliest activation site across the ablation line was determined.

Results

The double potential mapping located the conduction gap on a real-time basis without displaying any maps. There was no significant change in the accuracy between the different times after ablation and different pacing cycle lengths.

Conclusions

Double potential mapping locates the conduction gap on a real-time basis and would be useful in beating-heart epicardial ablation in off-pump setting.

Intracardiac acoustic radiation force impulse imaging: a novel imaging method for intraprocedural evaluation of radiofrequency ablation lesions

BACKGROUND

Arrhythmia recurrence after cardiac radiofrequency ablation (RFA) for atrial fibrillation has been linked to conduction through discontinuous lesion lines. Intraprocedural visualization and corrective ablation of lesion line discontinuities could decrease postprocedure atrial fibrillation recurrence. Intracardiac acoustic radiation force impulse (ARFI) imaging is a new imaging technique that visualizes RFA lesions by mapping the relative elasticity contrast between compliant-unablated and stiff RFA-treated myocardium.

OBJECTIVE

To determine whether intraprocedure ARFI images can identify RFA-treated myocardium in vivo.

METHODS

In 8 canines, an electroanatomical mapping-guided intracardiac echo catheter was used to acquire 2-dimensional ARFI images along right atrial ablation lines before and after RFA. ARFI images were acquired during diastole with the myocardium positioned at the ARFI focus (1.5 cm) and parallel to the intracardiac echo transducer for maximal and uniform energy delivery to the tissue. Three reviewers categorized each ARFI image as depicting no lesion, noncontiguous lesion, or contiguous lesion. For comparison, 3 separate reviewers confirmed RFA lesion presence and contiguity on the basis of functional conduction block at the imaging plane location on electroanatomical activation maps.

RESULTS

Ten percent of ARFI images were discarded because of motion artifacts. Reviewers of the ARFI images detected RFA-treated sites with high sensitivity (95.7%) and specificity (91.5%). Reviewer identification of contiguous lesions had 75.3% specificity and 47.1% sensitivity.

CONCLUSIONS

Intracardiac ARFI imaging was successful in identifying endocardial RFA treatment when specific imaging conditions were maintained. Further advances in ARFI imaging technology would facilitate a wider range of imaging opportunities for clinical lesion evaluation.

Identification and acute targeting of gaps in atrial ablation lesion sets using a real-time magnetic resonance imaging system

BACKGROUND

Radiofrequency ablation is routinely used to treat cardiac arrhythmias, but gaps remain in ablation lesion sets because there is no direct visualization of ablation-related changes. In this study, we acutely identify and target gaps using a real-time magnetic resonance imaging (RT-MRI) system, leading to a complete and transmural ablation in the atrium.

METHODS AND RESULTS

A swine model was used for these studies (n=12). Ablation lesions with a gap were created in the atrium using fluoroscopy and an electroanatomic system in the first group (n=5). The animal was then moved to a 3-tesla MRI system where high-resolution late gadolinium enhancement MRI was used to identify the gap. Using an RT-MRI catheter navigation and visualization system, the gap area was ablated in the MR scanner. In a second group (n=7), ablation lesions with varying gaps in between were created under RT-MRI guidance, and gap lengths determined using late gadolinium enhancement MR images were correlated with gap length measured from gross pathology. Gaps up to 1.0 mm were identified using gross pathology, and gaps up to 1.4 mm were identified using late gadolinium enhancement MRI. Using an RT-MRI system with active catheter navigation gaps can be targeted acutely, leading to lesion sets with no gaps. The correlation coefficient (R(2)) between the gap length was identified using MRI, and the gross pathology was 0.95.

CONCLUSIONS

RT-MRI system can be used to identify and acutely target gaps in atrial ablation lesion sets. Acute targeting of gaps in ablation lesion sets can potentially lead to significant improvement in clinical outcomes.