Applied Radiology

Dr. Marrouche and Dr. Natale are from the Section of Pacing and Electrophysiology, Department of Cardiovascular Medicine, Cleveland Clinic Foundation, Cleveland, OH.

This article was previously published in the publication Electromedica (2002;70:93-96). It is reprinted with the permission of Siemens AG (Erlangen, Germany) and the authors. ©2002 Siemens AG.

Introduction

Atrial ectopic beats within the pulmonary veins (PV) have been proven responsible for initiation of atrial fibrillation (AF). ¹ Different approaches have been developed to electrically confine PV triggers using longitudinal mapping, three-dimensional mapping systems, empirical anatomical isolation of the PV ostia, and circular mapping guided ostial isolation. ^1-7 This article will describe the use of intracardiac echo to monitor and guide PV isolation using the circular mapping approach in a patient with permanent AF.

Case Report

A 59-year-old white male with no structural heart disease and a history of symptomatic permanent AF since 1999 failed multiple antiarrhythmic drugs including flecainide, sotalol, amiodarone and dofetilide, and was referred to our laboratory for mapping and ablation of his arrhythmia.

A custom made catheter (Cardiac Assist Device Inc., Cleveland, OH) was advanced in the coronary sinus (CS). The proximal eight electrodes were positioned between the superior vena cava (SVC) and the high crista terminalis whereas the distal eight electrodes were in the CS. A transesophageal recording lead was used to record the left atrial posterior wall activation. A 10-F phase array intracardiac echo (ICE)-probe (AcuNav ^® Diagnostic Ultrasound Catheter, Acuson, a Siemens Company) was positioned in the right atrium using fluoroscopic guidance. Mapping of the left atrium and pulmonary veins (PV) was completed after approaching the left atrium via a transseptal approach. Two separate ICE-guided (Figure 1) transseptal punctures were obtained. A 6-French multielectrode circular mapping catheter (Lasso, Biosense-Webster, Baldwin Park, CA) with a deflectable shaft and 2 cm diameter loop was used to map ostial PV potentials.

Besides guiding the transseptal approach, the phase array ICE probe (AcuNav catheter, Acuson) appeared useful to define the PV ostia and to monitor energy delivery. The circular mapping catheter was positioned at the PV ostium. Correct placement was obtained through the ICE image (Figure 2). Radiofrequency energy was delivered using a power controlled cooled-tip ablation catheter (50 Watt generator; EPT, Sunnyvale, CA). Energy delivery was titrated to the maximum value within 45­60 seconds. Energy delivery was terminated after 45­60 seconds. ICE was utilized to monitor bubble formation. ^8-10 Two types of bubble patterns were seen with ICE. This included bubbles limited to the area around the ablation catheter (type 1), reflecting appropriate lesion formation versus a shower of dense bubbles extending to the left atrial cavity (type 2) and reflecting tissue overheating (Figure 3). Dense generation of bubbles appeared to precede impedance elevation by a few seconds. Intravenous heparin was titrated to maintain the activated clotting time (ACT) between 350 and 400 sec after the transeptal puncture.

The patient was presented to the electrophysiology laboratory in AF with ventricular response of 98 bpm. After positioning the Lasso catheter in the left upper PV (LUPV) and the ablation catheter in the right upper PV (RUPV), DC cardioversion was performed. Early recurrence of AF initiated by an atrial premature contraction from the LUPV was documented. ICE guided isolation of the LUPV and left lower pulmonary vein (LLPV) ostia were performed during AF. The maximum power, temperature and impedance during energy delivery were 40 Watts, 40°C and 173 Ohms, respectively. Type 2 bubbles occurred 6 times during ablation. Table 1 lists energy parameters associated with type 2 bubbles formation.

Following isolation of the left PVs, repeated DC cardioversion was successful and the patient was maintained in sinus rhythm. Isolation of RUPV and right lower pulmonary vein (RLPV) was then conducted in the same manner.

Doppler flows of all four PV were recorded prior, during, and after PV isolation. The diastolic flow velocities were 0.6 m/s in the LUPV, 0.48 in the LLPV, 0.7 in the RUPV and 0.6 in the RLPV before ablation, versus 0.7 m/s in the LUPV, 0.6 in the LLPV, 0.8 in the RUPV and 0.8 in the RLPV after isolation.

At six months follow-up, the patient was still in sinus rhythm off antiarrhythmic drugs. A spiral CT scan was conducted 3 months after ablation and excluded PV stenosis.

Conclusion

Intracardiac echo facilitates PV isolation by 1) rendering transseptal access easier and safer; 2) by helping in proper placement of the circular mapping catheter at the vein ostium; and 3) by optimizing power titration during radiofrequency energy delivery through detection of bubbles at the catheter-tissue interface. Prompt detection of dense bubbles (type 2 bubbles) could also prevent impedance rise and avoid the milieu for thrombus formation. In addition, monitoring PV flow velocity offers the potential to prevent excessive swelling at the PV ostium, which could lead to chronic PV stenosis. In this respect, ablation at the PV ostium should be aborted when the PV diastolic flow velocity exceeds 1 m/sec. *