CORRESPONDENCE: RESEARCH CORRESPONDENCE
Single-Step Atrial Thrombus Exclusion and Internal Cardioversion of Atrial Fibrillation Via a Transesophageal Echocardiography Probe
Thomas Schimpf, MD,
Karl Mischke, MD,
Jurgita Plisiene, MD,
Pal Soos, MD,
Christian Knackstedt, MD,
Markus Zarse, MD,
Felix Gramley, MD,
Lajos Patonay, MD,
Veronica Molina, MD, MSEE,
Bela Merkely, MD,
Peter Hanrath, MD, FACC and
Patrick Schauerte, MD*
* Department of Cardiology, RWTH Aachen University, Pauwelsstr. 30, 52074 Aachen, Germany (Email: pschauerte{at}ukaachen.de).
To the Editor: Atrial thrombus exclusion by transesophageal echocardiography (TEE) prior to cardioversion (CV) of atrial fibrillation (AF) shortens the time to CV and reduces hemorrhagic complications compared to a three- to four-week period of oral anticoagulation before CV (1). Because of the proximity of the TEE probe to the atria, disposable CV electrode sheaths were developed that can be affixed to conventional TEE-probes to perform TEE thrombus exclusion and internal TEE-CV in one procedure.
For TEE-CV, single-use latex sheaths (length 130 cm) with integrated large (15.15 cm2) or small (7.15 cm2) CV electrodes were applied (Fig. 1). The thin foil electrode is embedded in a soft synthetic pad, which is incorporated into the sheath. Thus, when the TEE probe enters the esophagus, the electrode easily bends and attaches to the TEE probe. Next, 10 cc of ultrasound gel was filled into the distal sheath reservoir. A TEE probe (OmniPlane, Philips Medical Systems, Andover, Massachusetts) was next introduced into the sheath, with the tip positioned in the distal reservoir.
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Figure 1 Plastic sheath with integrated cardioversion (CV) electrodes covering a conventional transesophageal echocardiography (TEE) probe.
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Six TEE-CV configurations were tested: small proximal versus small distal esophageal electrode (B), small gastric versus small esophageal electrode (C), small esophageal electrode versus two external patches (D), large esophageal electrode versus two external patches (E), large esophageal electrode versus single external patch (F), two small esophageal electrodes versus two external patches (G). The two esophageal electrodes of configurations B, C, G were separated by 10 cm.
For transvenous cardioversion (TV-CV) (H), a CV catheter (Alert, EP MedSystems, West Berlin, New Jersey) consisting of two CV coils was advanced into the left pulmonary artery under fluoroscopy. For external CV two cutaneous self-adhesive patch electrodes (Quick-Combo, Medtronic Physiocontrol, Redmond, Washington) were attached to the chest in a right lateral and left apical position (A).
For external and TEE-CV biphasic shocks were delivered from a Heartstream-XL defibrillator (Philips Medical Systems) and for TV-CV from a HVS-02 defibrillator (Ventritex Corp., Sunnyvale, California).
A randomized step-up/step-down CV protocol was tested in 15 anesthetized pigs; AF lasting longer than 20 s was induced by atrial burst pacing. After AF induction, 10 s elapsed until shock delivery. At least 3 min passed after CV. In six dogs, esophagoscopy was performed immediately after and six weeks following delivery of three high-energy TEE-CV shocks (150 J, 200 J, 200 J, configuration E). Thereafter, the esophagus was excised for macroscopic and histological evaluation.
Data are presented as mean ± 1 SD. Both analysis of variance and the Student paired t tests were applied to compare atrial cardioversion thresholds (ACVTs). A value of p < 0.05 was considered significant.
The average AF duration was 29 ± 11 s. The TEE-CV sheath did not compromise the handling of the TEE probe or image quality. In all animals the left atrial appendage could be scanned for thrombus exclusion from 0° to 180° transesophageal views. No sheath broke during introduction into the esophagus or repeated shock delivery. The depth of the CV electrode differed between animals depending on the distance from the incisors to the esophageal position at which the atria could be visualized. Thereby, TEE allowed positioning of the CV electrode precisely behind the atria tailored to the individual animal’s anatomy.
The highest ACVT was observed for external CV (45.3 ± 21.2 J, p < 0.001) (Fig. 2). The TEE-CV resulted in significantly lower ACVTs than external CV. The lowest ACVT was obtained with configuration E (11.8 ± 8.6 J), yielding a four-fold energy reduction compared to external CV (configuration A, p < 0.001). The TEE-CV (configuration E) was equally effective as TV-CV (configuration H, 10.1 ± 5.8 J, p = NS).
Esophagoscopy immediately after repeated high-energy TEE-CV in six dogs revealed slight mucosal hyperemia in two dogs. After six weeks the esophagus was not damaged in any dog, including the two with initial hyperemia as judged by esophagoscopy and macroscopic and microscopic inspection. Subsequent histological examination did not show necrosis, erosion, ulceration, or regenerative changes.
In 1966, McNally et al. (2) proposed transesophageal CV of AF which has never enjoyed widespread clinical use. Meanwhile, TEE is increasingly used to exclude atrial thrombi prior to CV (1). The present study describes how these two beneficial elements can be combined in one procedure. The simplicity of the combined CV/imaging system and its ease of use distinguish this approach from previous transesophageal CV attempts. These investigations employed esophageal CV catheters, which were mostly positioned under fluoroscopic control (3–5). Some included atrial CV electrodes (3,6) or delivered shocks between esophageal and cutaneous electrodes (4,5) or mere esophageal electrodes (5,7). The approach presented herein also differs from a recent report on transesophageal CV in patients with CV electrodes embedded permanently in a novel TEE-probe (8) as the disposable CV electrode sheath can be affixed to any conventional TEE probe already available in the hospitals. It also enables the continued use of disposable sheaths to cover the TEE probe for hygienic reasons as practiced in many hospitals. By contrast, TEE-CV electrodes permanently integrated into a TEE probe would prevent the use of isolating plastic sheaths.
Safety of the approach is an important concern. Chronic follow-up of the dogs with high-energy TEE-CV did not reveal esophageal damage. Because esophagoscopies were not undertaken in the six-week interval between CV and final examination, we cannot exclude that initial hyperemia in two animals transiently progressed to erosive esophagitis or ulceration. The lack of chronic esophageal damage, however, provides evidence that TEE-CV may be performed safely in patients. Finally, because AF was acutely induced we cannot determine whether TEE-CV would be as effective in chronic AF or with underlying atrial pathology.
In brief, TEE-CV of AF led to a four-fold reduction of CV energy compared to external CV and was equally effective as TV-CV. The CV electrode can be attached to conventional TEE probes and may allow CV and thrombus exclusion during one sedation.
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Footnotes
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Please note: Drs. Mischke and Schimpf contributed equally to this paper. Dr. Plisiene is the recipient of a grant from the German Academic Exchange Foundation (DAAD). The experiments were in part supported by a grant from Philips Medical Systems.
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References
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