Background: Postoperative atrial fibrillation (POAF) is defined as new-onset AF in the immediate postoperative period. The relatively high incidence of POAF after cardiac surgery is well described, but pathophysiological mechanisms underlying the initiation, maintenance, and progression of POAF may be multifactorial and have not yet been comprehensively characterized. One of the mechanisms includes altered Ca2+ kinetics. Accumulating evidence has suggested that altered atrial cytosolic calcium handling contributes to the development of POAF, protamine reversibly modulates the calcium release channel/ryanodine receptor 2 (RyR2) and voltage-dependent cardiac RyR2. However, it is currently unknown whether such abnormalities contribute to the arrhythmogenic substrate predisposing patients to the development of POAF. Methods: We have retrospectively analyzed 147 patients who underwent cardiac surgery with cardiopulmonary bypass support. Of these, 40 patients were excluded from the analysis because of pre-existing AF. All patients received heparin followed by protamine at different dosing ratios of protamine-to-heparin, depending on the periods studied. Results: The dosing ratio of protamine-to-heparin = 1.0 was compared with higher dosing ratios of protamine-to-heparin >1.0 up to 1.7. POAF developed in 15 patients (15/107 = 14%), of these, 5 out of 57 patients (33.3%) in the dosing ratio of protamine-to-heparin = 1.0 and 10 out of 35 patients (66.7%) in the higher dosing ratios of protamine-to-heparin. Statistical significance was observed in patients with higher dosing ratios of protamine-to-heparin, compared with the dosing ratio of protamine-to-heparin = 1.0 (odds ratio = 3.890, 95% CI = 1.130–13.300, p-value = 0.031). When types of diseases were analyzed in terms of higher dosing ratios of protamine-to-heparin, only valvular disorders were significantly associated with POAF (p = 0.04). Conclusions: Protamine is clinically utilized to reverse heparin overdose and has been shown to display immunological and inflammatory alterations. However, its association with POAF has not been reported. Our results provide evidence that higher dosing ratios of protamine-to-heparin may increase the incidence of POAF.

Preservation of subvalvular mitral apparatus and maintenance of continuity between structures and annulus is recognized, and widely accepted as a significant factor for avoiding impairment to ventricular function and preventing left ventricular rupture during mitral valve replacement. However, we encountered a patient who developed posteromedial papillary muscle rupture following chordal sparing mitral valve replacement. The patient was a 67-year-old man who underwent mitral valve replacement with a porcine bioprosthesis 29M for acute mitral valve insufficiency due to several spontaneous chordal ruptures. The subvalvular apparatus of both leaflets was retained, the center of the anterior leaflet was excised elliptically, and the entire posterior leaflet was preserved. Although his postoperative course was uneventful, the transthoracic echocardiogram showed a floating structure prolapsing through the aortic valve in the left ventricle synchronizing with the cardiac cycle. The severed papillary muscle was removed successfully via an aortotomy through the native aortic valve on the 57th day after the first surgery. The patient recovered with no events. Surgeons should consider avoiding an excessive tension on the preserved chordae and delivering a cardioplegia sufficiently and uniformly during mitral valve replacement. Jpn. J. Cardiovasc. Surg. 42 : 416-419(2013) Keywords：mitral valve replacement, rupture of papillary muscle, preservation of chordae, chordal sparing mitral valve replacement, subvalvural apparatus

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