Author + information
- Received October 11, 2016
- Revision received November 20, 2016
- Accepted November 28, 2016
- Published online June 19, 2017.
- Markus B. Sikkel, MBBS, PhDa,b,∗ (, )
- Vishal Luther, MBBSa,b,
- Arunashis Sau, MBBSa,
- Fernando Guerrero, BScc,
- Fu Siong Ng, MBBS, PhDa and
- Phang Boon Lim, MB, BChir, PhDa,b
- aMyocardial Function Section, National Heart and Lung Institute, Imperial College London, London, United Kingdom
- bDepartment of Electrophysiology, Imperial College Healthcare National Health Service Trust, Hammersmith Hospital, London, United Kingdom
- cBoston Scientific, Hemel Hempstead, Herts, United Kingdom
- ↵∗Address for correspondence:
Dr. Markus B. Sikkel, Myocardial Function Section, Fourth Floor, Imperial Centre for Translational and Experimental Medicine, Imperial College London, Hammersmith Campus, Du Cane Road, London W12 0NN, United Kingdom.
Electroanatomical mapping technology has developed rapidly over recent years. The Rhythmia mapping system (Boston Scientific, Natick, Massachusetts) has been described in detail elsewhere (1). Briefly the system involves automated collection of anatomical and electrogram data from the atrium, with rapid, high-density acquisition facilitated by the use of the system in conjunction with the Orion catheter. This mini-basket (1.8 cm diameter) contains 8 splines of 8 low-impedance electrodes with a surface area of 0.4 mm2 and a 2.5-mm interelectrode spacing. Maps we have collected in an initial series of patients have been highly detailed with >100 points/cm2 in atrial maps. Whether this increased density can translate into enhanced efficacy in the identification and ablative therapy of atrial arrhythmias is not yet clear. We illustrate an example case in which a high point density allowed identification of a site of epicardial to endocardial breakthrough of an incomplete mitral isthmus line, facilitating spot ablation at the site to terminate the arrhythmia and block the line.
A 71-year-old man with known ischemic heart disease and moderate impairment of left ventricular systolic function was reviewed in clinic due to worsening dyspnea. He had a history of recurrent atrial tachycardia (AT) following surgical ablation for persistent atrial fibrillation (box lesion set around all 4 pulmonary vein ostia with Epicor focused ultrasound ablation system [St. Jude Medical, St. Paul, Minnesota) 6 years previously at the time of coronary artery bypass graft. In the intervening years, he had had 3 further percutaneous AT ablations.
On this occasion during his clinic visit, he was diagnosed with a recurrence of AT (Figure 1). Under general anesthesia, femoral venous access was obtained and a steerable decapolar catheter inserted into the coronary sinus (CS). Endocardial mapping was performed using Rhythmia mapping system (Boston Scientific) and IntellaMap Orion high-resolution mapping catheter (Boston Scientific). Following transseptal puncture, a left atrial activation map was created (21,763 points over a surface area of 136.8 cm2 in 32 min 44 s—159 points/cm2, 11.1 points/s). The posterior wall was electrically silent and surrounded by low-voltage areas consistent with scar, but with sufficient healthy atrial tissue to maintain perimitral flutter around the annulus (Figure 2A). A narrow isthmus of healthy tissue amid scar was identified at the inferolateral aspect of the mitral annulus. Ablation was performed across this isthmus (Figure 2B) with further ablation in the mid-portion of the CS with an open-irrigated Thermocool ablation catheter (Biosense Webster, South Diamond Bar, California) at 30 W (20 W for CS), 17 ml/min irrigation. This prolonged the cycle length to 274 ms but did not terminate the tachycardia.
The left atrium was partially remapped around mitral isthmus during this new atrial tachycardia using the same beat acceptance criteria and resulting in automatically collected activation and voltage maps (9,011 points over a surface area of 112.8 cm2 in 11 min 20 s—79.9 points/cm2, 13.25 points/s). A map of activation within the CS was also collected via the decapolar catheter. Together these maps showed slow conduction along the CS, followed by electrical silence for 31 ms, followed by breakthrough of activation from a point adjacent to the posterior scar and propagation around the mitral annulus to complete the circuit (Figure 2C, Online Video 1). A single 60-s lesion at the point of breakthrough slowed and then terminated the tachycardia to sinus rhythm and produced mitral isthmus (MI) line block. This ablation of focal epi-endocardial breakthrough was facilitated by high-density mapping and illustrates a way around this particular challenge in MI line completion.
Other challenges are well known to obstruct the creation of a successful MI line. These barriers to effective ablation include anatomical factors. These have been elegantly illustrated through analysis of post-mortem specimens (2) including length of the MI line required (35 ± 7 mm) and heat sinks in close proximity such as the CS and circumflex artery. The same study showed that a proximal isthmus line, as performed in this case, can pose additional challenges. For example, the myocardium is much thicker in this region (up to 5.2 ± 1.8 mm vs. 3.8 ± 0.9 mm at a standard location) and there is a higher likelihood of encountering a muscular sleeve around the CS (92% vs. 19% at a standard location) although there is less risk of arterial damage when ablating proximally. In our case, a proximal location was selected because previous ablation had left a narrow isthmus here and so patient-specific factors are also important. A further challenge in some cases is that the ligament of Marshall can allow continued propagation of perimitral AT via an endo-epicardial connection, usually located at the ridge between left upper pulmonary vein and appendage (3).
In summary, we report a case in which high-density electroanatomical mapping facilitated successful ablation of an AT. The case effectively illustrates an aspect of the difficulty in attaining MI block via radiofrequency ablation—namely epi-endocardial connection via the CS. Due to the high density of mapping points, it also shows that such connections can exist via focused (accessory pathway-like) strands of conducting tissue leading to very focal breakout from a small region of endocardium.
Dr. Sikkel is supported by a National Institute of Health Research Clinical Lectureship Award (#2670). Dr. Guerrero is an employee of Boston Scientific (Rhythmia coordinator and technical support). Dr. Ng has received speaker honorarium from Boston Scientific. Dr. Lim has received speaker honoraria and research grants from Boston Scientific. All other authors have reported that they have no relationships relevant to the contents of this paper to disclose.
All authors attest they are in compliance with human studies committees and animal welfare regulations of the authors’ institutions and Food and Drug Administration guidelines, including patient consent where appropriate. For more information, visit the JACC: Clinical Electrophysiology author instructions page.
- Received October 11, 2016.
- Revision received November 20, 2016.
- Accepted November 28, 2016.
- 2017 American College of Cardiology Foundation
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