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Ann Thorac Surg 2007;84:1073
© 2007 The Society of Thoracic Surgeons
Department of Cardiac Surgery, Hospital de Enfermedades Cardiovasculares y del Tórax, UMAE # 34, Instituto Mexicano del Seguro Social, Ave Lincoln y Maria de Jesús Candia s/n, Col Valle Verde 2do Sector, Monterrey, Nuevo León, 64400 Mexico
(Email: ovidio{at}voila.fr).
I read the article of Lukac and colleagues [1] with great interest. They showed that the superior septal approach (SSA) caused serious sinus rhythm disturbances when compared with the classical left atrial approach (LAA) for mitral valve (MV) surgery. In fact, 17 of 150 patients with SSA and 27 of 427 patients with LAA needed pacemaker implantations. Of these cases, 9 and 10 cases, respectively (p = 0.010), had a pacemaker implanted because of sinus node dysfunction. So the authors concluded that SSA has higher risk of sinus node dysfunction than conventional LAA for MV surgery. Damage to the sinus node artery and isolation of the posterior area of the right atrium with the sinus node zone included are some of the pathologic mechanisms mentioned in this article.
The great concern in SSA related to the "unavoidable" division of the sinus node artery and its further consequences on cardiac rhythm is not absolutely understood yet.
In 2003, we reported a series of 128 cases operated on using the SSA for MV surgery [2]. In this study, PR interval was shorter than normal (100 ± 30 msec) and P wave morphology changed becoming inverted in leads II, III, and aVF. However, we observed a whole recuperation into normal measurements, both the PR interval and P wave axis in 86.7% of patients (ie, 52 of 60 patients) who experienced these electrical disturbances. At a late follow-up, only 2 patients with previous normal sinus rhythm were in junctional rhythm after the third postoperative month. These 2 patients needed definitive pacemaker implantation.
One has to keep in mind two conditions: (1) once the sinus node artery is completely transected, a period of instability termed "atrial chaos" [3] appears and is seen during 1 to 2 weeks; and (2) then a regular atrial rhythm usually develops at a slower rate with no clinical impact for most of the cases, and this usually persists for as long as 3 months.
Several explanations have been proposed. Misawa and colleagues [4] mentions the development of collateral blood supply on the sinus node area, arising 2 weeks after surgery. Sealy and colleagues’ concept [5] is very interesting, which is that the lack of normal sinus rhythm as a result of the surgical division of the sinus node artery provokes the genesis of a new atrial rhythm on the coronary sinus area with little if any change in electrocardiogram; this is almost undistinguishable from normal sinus rhythm. This electrical impulse would travel up the posterior internodal tract to the right atrial appendage and up the anterior tract of Bachman’s bundle to the left atrial appendage. The development of stability could be an adjustment, inherent to the pacemaking cells, which seems to render the low atrial area predominantly, as well as being a reliable pacemaker.
Nevertheless, in spite of most of all these electrical changes seems to be transient, special attention must be taken in the first 3 postoperative months, because many patients depend critically of the normal sinus rhythm.
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  P. Lukac, V. E. Hjortdal, and P. S. Hansen Reply Ann. Thorac. Surg., September 1, 2007; 84(3): 1073 - 1074. [Full Text] [PDF]
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