Original-experimentalAtrial fibrillation propagates through gaps in ablation lines: Implications for ablative treatment of atrial fibrillation
Introduction
Atrial fibrillation (AF) is the most common sustained arrhythmia in the world, occurring in 0.4%–2.0% of the general population.1 The Cox-maze procedure (CMP) was developed in the 1980s and has the highest reported long-term success for the treatment of AF.2 Because the CMP is technically challenging and time-consuming to complete, few surgeons choose to incorporate it into their daily practice. Recent advancements in technology have made it possible to replace many of the incisions with linear lines of ablation, making the procedure both shorter and less technically challenging. Various energy sources, including radiofrequency, microwave, laser, cryoablation, and high-frequency ultrasound, have been used.3
There are many contributing factors that can determine success in ablation for either catheter-based or surgical treatment of AF. These include the number and location of the lesions, the mass of atrial tissue ablated, the successful isolation of triggers, and the effectiveness of the particular technology in terms of ablation depth and width. An important question that has arisen is whether having transmural or complete lesions is important or necessary. In a chronic canine model, Ishii et al4 found that conduction block rarely occurred in gaps larger than 5 mm, and decremental slowing was seen in gaps between 5 and 15 mm. In this model, in which gaps were left in surgical incision lines, complete block was seen in gaps smaller than 5 mm. In another canine model in which gaps were left in lines created by unipolar radiofrequency, conduction block was rarely seen with a gap greater than 5 mm and was variable at 2–5 mm of gap.5 Conduction was demonstrated down to a gap of 0.1 mm in an acute canine laser model, substantiating that even very small breaks in ablation lines have the ability to conduct paced impulses.6 In an in vivo study by Inoue and Zipes,7 conduction was found in atrial tissue with a cross-sectional area as little as 1 mm2.
This study was designed to test the following hypotheses: paced conduction would be slowed and eventually blocked with a decrease in gap size and block of conduction of AF through gaps would occur with decreasing gap size.
Section snippets
Methods
All animals received humane care in compliance with the National Academy of Sciences 1996 Guide for the Care and Use of Laboratory Animals. Normal mongrel dogs (n = 13), weighing between 20 and 30 kg, were intravenously anesthetized with 7.5 mg/kg of propofol, intubated, and placed on a positive pressure respirator with 2%–3% isoflurane used throughout the procedure. A median sternotomy was performed, and the heart was cradled in the pericardium. The interatrial groove was dissected, separating
Results
Gap widths were examined from a range of 1.1 to 11.2 mm. Paced conduction velocity slowed as gap size decreased (P <.002; Figure 3). Conduction velocity (Figure 4) was dependent on PCL, as decreased cycle lengths had decreased conduction velocity (P = .001). Pacing direction did not have a significant impact on conduction velocity independent of gap size (P = .192). The mean control ERP was 166 ± 3.9 ms, and the preablation ERP with ACh was 41 ± 3.2 ms. After the fifth ablation, the ERP ACh was
Discussion
This study demonstrated that despite a correlation of decreased conduction velocity with smaller gaps in the ablation line, electrical impulses were still propagated even at very narrow gap widths. The results were similar for paced wave fronts and AF, with consistent conduction persisting in residual gaps greater than the smallest obtainable gap size in this model (∼1 mm). In the vast majority of samples, complete ablation was required to prevent conduction of both paced and AF electrical
Limitations
This model has several limitations. The canine atria were normal, not diseased, and thus results may not be directly comparable to the diseased human atria. However, the canine is an excellent model for testing AF and has been used previously for this purpose.21 This model evaluated residual gaps that included full-thickness intact atrial tissue, which may be different than residual endocardial or epicardial rims of tissue. However, wide superficial ablation lines with residual endocardial or
Conclusion
Propagation of paced signals occurred through narrow gaps left in ablation lines on the atrium, even when conduction velocities were significantly slowed. In addition to propagation of paced signals, the majority of narrow residual gaps conducted AF. A close correlation was seen between the propagation of paced signals and AF, suggesting that pacing can be used as a surrogate to ensure adequacy of a lesion. To guarantee complete conduction block in this model, continuous transmural lines of
References (22)
- et al.
Incisional atrial reentrant tachycardia: experimental study on the conduction property through the isthmus
J Thorac Cardiovasc Surg
(2003) - et al.
Combined endocardial and epicardial radiofrequency ablation of right and left atria in the treatment of atrial fibrillation
Ann Thorac Surg
(2001) - et al.
Simple left atrial procedure for chronic atrial fibrillation associated with mitral valve disease
Ann Thorac Surg
(1996) - et al.
The surgical treatment of atrial fibrillationIII. Development of a definitive surgical procedure
J Thorac Cardiovasc Surg
(1991) - et al.
Late recurrent arrhythmias after ablation of atrial fibrillation: incidence, mechanisms, and treatment
Heart Rhythm
(2004) - et al.
Microwave ablation for atrial fibrillation: dose-response curves in the cardioplegia-arrested and beating heart
Ann Thorac Surg
(2006) - et al.
Prevalence, age distribution, and gender of patients with atrial fibrillationAnalysis and implications
Arch Intern Med
(1995) - et al.
The Cox maze III procedure for atrial fibrillation: long-term efficacy in patients undergoing lone versus concomitant procedures
J Thorac Cardiovasc Surg
(2003) - et al.
Advances in surgical ablation devices for atrial fibrillation
- et al.
Morphological and physiological characteristics of discontinuous linear atrial ablations during atrial pacing and atrial fibrillation
J Cardiovasc Electrophysiol
(1999)
The effect of a residual isthmus of surviving tissue on conduction after linear ablation in atrial myocardium
J Interv Card Electrophysiol
Cited by (71)
The Cox-Maze procedure: What lesions and why
2023, JTCVS TechniquesBipolar Ablation for an Intramural Septal Atrial Tachycardia
2023, Cardiac Electrophysiology ClinicsCryoablation Cox-maze Surgery: Nitrous Oxide or Argon? Putting the Debate on Ice
2022, Annals of Thoracic SurgeryPathophysiology of Atypical Atrial Flutters
2022, Cardiac Electrophysiology ClinicsCitation Excerpt :Whatever the underlying heart disease, the described atrial substrate modification may lead to slow-conducting areas that represent the pathophysiological hallmark of AAFL.8,27,28 In an elegant experimental study conducted on canine hearts, Melby and colleagues showed that anatomic gaps left between ablation lines were associated with slow conduction, and the narrower the gap the slower the conduction velocity.27 Similar observations were recorded in human beings undergoing both conventional and three-dimensional electroanatomic mapping for post-CPVA AAFL.8
Isolated left atrial cryoablation of atrial fibrillation in conventional mitral valve surgery
2020, IJC Heart and VasculatureBipolar Radiofrequency Ablation on Explanted Human Hearts: How to Ensure Transmural Lesions
2020, Annals of Thoracic Surgery
Funded in part by National Institutes of Health grant nos. RO1-HL032257, R01-HL085113, and F32 HL078136-01.
Dr. Damiano is a consultant for Atricure, Inc., and Medtronic Corporation. Dr. Schuessler is a consultant for Atricure, Inc.