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J Thorac Cardiovasc Surg 2003;126:914-916
© 2003 The American Association for Thoracic Surgery
Brief communications |
a Divisions of Cardiac Surgery and Cardiology, Ospedale San Raffaele, Milan, Italy
Received for publication December 13, 2002; accepted for publication December 27, 2002.
* Address for reprints: João Melo, Hospital Santa Cruz, Av. Prof. Dr. Reinaldo Dos Santos 27, 2790—136 Carnaxide, Portugal
joaomelo100{at}hotmail.com
In mitral patients the origin and mechanisms of atrial fibrillation are largely unknown. Even though several theories have been postulated for its origin, there is scarce evidence to support them. Surgical procedures that electrically isolate the pulmonary veins from the left atrial chamber are associated with a very high success rate. We report a case of a mitral patient with permanent atrial fibrillation who underwent mitral valve replacement and extended bilateral isolation of the pulmonary veins using intraoperative radiofrequency ablation. After surgery, bidirectional electrical block from the right pulmonary veins was documented.
Postoperative epicardial recordings and Holter monitoring showed paroxysmal tachycardia limited to the atrial cuff of the right pulmonary veins while the patient remained in stable sinus rhythm.
Clinical summary
This 56-year-old female patient had severe mitral valve stenosis with moderate regurgitation, tricuspid regurgitation, and permanent atrial fibrillation of 10 months’ duration. She was in New York Heart Association class functional II, with a peak systolic pulmonary artery pressure of 50 mm Hg and moderate tricuspid regurgitation.
Under cardiopulmonary bypass and moderate hypothermia, the mitral valve was replaced, preserving the posterior leaflet, with a St Jude Medical 27 prosthesis (St Jude Medical, Inc, St Paul, Minn), and the tricuspid valve was repaired with a Kay annuloplasty.
Myocardial protection was achieved with antegrade and retrograde blood cardioplegia. Before the valve procedure, extended bilateral isolation of pulmonary veins as previously described by some of us1 was performed using radiofrequency ablation with a temperature-controlled catheter (Cobra, Boston Scientific, San Jose, Calif). The left atrial appendage was suture-closed from inside the atrium. Crossclamp and cardiopulmonary bypass durations were 122 and 102 minutes, respectively. Prophylactic treatment with amiodarone was initiated during surgery.
Before closing the chest, 3 bipolar temporary pacing wires (Streamline 6495; Medtronic, Minneapolis, Minn) were inserted: one in the roof of the left atrium, one in the midpart of the right atrium, and the last inside the encircled portion of the right pulmonary veins.
Bipolar pacing thresholds from the right atrium and left atrium were 0.8 and 0.6 mAmp, respectively. From the right pulmonary veins cuff, using a maximum output of 20 mAmp, pacing was not possible. The postoperative course was uneventful; the patient required assisted ventilation for 12 hours and blood drainage was 500 mL. The patient regained and maintained sinus rhythm after surgery.
Thirty-six hours after surgery, recordings using the wires connected to 3 different epicardial locations were performed (Figure 1). The patient was in normal sinus rhythm, but still the right pulmonary veins cuff was in atria tachycardia/atrial fibrillation. From the third to the fifth postoperative day, Holter monitor recording using the epicardial wires was performed. Except for a short period of similar tachycardia in the right pulmonary veins cuff, the patient remained in sinus rhythm all the time (Figure 2).
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Discussion
The mechanisms underlying the origin of atrial fibrillation remain to be fully understood. Observations from the last 5 years challenge the dominant concept of multiple wavelet reentry mechanisms of the early 1990s.2 Interestingly, in mitral patients, these mechanisms have never been fully investigated. The pulmonary veins as the point of origin or perpetuation of atrial fibrillation was postulated in 19243 and clinically evident in 1998.4,5 Still there has been no report on the specific events leading to atrial fibrillation in mitral patients. Using direct epicardial readings from the 2 atria, after radiofrequency ablation we documented an electrical block line around the right pulmonary veins. The excluded area of the atria showed self-terminating episodes of pulmonary vein tachycardia with no effect on the heart rhythm.
These findings prove that in selected patients, the connection of the right pulmonary veins to the atria is responsible for an increased excitability, likely related to the presence of much shorter refractory periods of the myocytes in the area.
Further studies are required to fully understand the role of the contralateral pulmonary veins and additional mechanisms that may be present, either in patients with lone atrial fibrillation or with atrial fibrillation and concomitant heart disease.
Atrial readings from the epicardium are easy and useful; they will help improve our knowledge of the origin and maintenance of atrial fibrillation in patients undergoing cardiac surgery. The data obtained from these patients are of utmost importance as they will lead to better understanding of the current concepts about atrial fibrillation.
References
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