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J Thorac Cardiovasc Surg 2005;130:234
© 2005 The American Association for Thoracic Surgery
Letters to the Editor |
Department of Cardiothoracic Surgery, Nippon Medical School, Tokyo, Japan
I appreciate the comments by Dr Shanmugam.
All surgical procedures are based on the anatomic or physiologic conditions, and thus so should be the operation for atrial fibrillation (AF). The most challenging but exciting issue in surgical intervention for arrhythmias is that the lesions responsible for maintaining the arrhythmias are not usually visible by use of the ordinary approaches. We found intraoperative mapping to be useful in determining the mechanism of AF and the optimal procedure in each patient. The patients who underwent the simple procedure were selected only on the basis of the results of the analysis in the study. If the patients with right atrial reentry had undergone the simple procedure, the AF would not have been converted to sinus rhythm.
The mapping technique requires further refinement. The pattern of atrial activation could not be determined on the basis of the intraoperative analysis in some patients. In about half of those patients, the atrial activation was complex, and it took several hours to determine the activation pattern through a postoperative offline analysis. Some preoperative examination method should be developed to determine whether the AF is maintained by rapid activation arising from a pulmonary vein (PV) alone or a combination with reentrant physiology and to determine the optimal procedure preoperatively.
A mapping technique would be helpful rather in verifying conduction block across each ablation lesion and in assessing the inducibility of AF. This assessment would be practical and crucial in off-pump AF ablation. The intraoperative mapping would enable a stepwise approach to AF in the off-pump setting, in which the atria could be mapped again after the successful isolation of the PVs to determine the indication for atrial linear ablation and the location of each lesion.
The transition from intermittent to continuous AF might be contiguous and related to the pathophysiology of the atrial myocardium, such as fibrosis of the myocardium combined with spatiotemporal dispersion of the refractoriness and conduction velocity. These abnormalities might be correlated to the left atrial (LA) diameter, the duration of AF burden, and other clinical conditions. There was an insignificant difference in the LA diameter between the patients with continuous and intermittent AF in our clinical experience. However, we believe the procedure should not be determined on the basis of the clinical findings alone because all those clinical parameters did not directly correlate to the above pathophysiologic conditions.
Most of the patients exhibited coexisting repetitive activations arising from 2 or more PVs. Interestingly, the distribution of the focal activation was dominantly from the right and left superior PVs. Isolating the right or left superior PV alone with an LA cuff would be technically difficult and unsafe. The superior and inferior PVs should be isolated bilaterally from the respect of prophylaxis and the surgical technique.
The focal activation from the LA appendage might be an epicardial breakthrough of the activation arising from the left superior PV, conducting through the pectinate muscle endocardially. The LA appendage should be excised not because there can be a focal firing from the appendage but because the risk of thromboembolism should be reduced by all possible means in the patients who are not cured of AF or whose LA contraction was not sufficient after the operation.
Intraoperative mapping of AF is not as simple as we have experienced in Wolff-Parkinson-White syndrome. The results of the data analysis might not necessarily be useful in each patient but might be helpful in understanding this troublesome tachyarrhythmia and in developing a definitive procedure.
Related Article
J. Thorac. Cardiovasc. Surg. 2005 130: 234.
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