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Ann Thorac Surg 2004;78:83-84
© 2004 The Society of Thoracic Surgeons
Cardiothoracic Surgery, Royal Victoria Hospital, Grosvenor Rd, Belfast BT12 6BA, UK
e-mail: olelund{at}ntlworld.com
This interesting and potentially important paper represents a large, single-center experience over a sufficiently long period to describe the remaining life of the average adult patient after left-side valve replacement. The majority of the implanted prosthetic valves are in current use, which adds strength to the use of the paper's conclusions in current decision making.
There are two potential sources of error, however, which could lead both to underestimation of stroke rates and to bias in multivariable statistical analysis. A total of 741 patients (23%) were lost to follow-up after a mean of 4.5 years, and deaths from unknown causes were treated as censored events. Drop-outs in a follow-up process, especially involving outpatient clinic visits, usually disappear for a reason, and debilitating or fatal stroke could be one such reason. Deaths from unknown causes are usually of the "sudden unexpected" variety, which could also hide a stroke.
It should be noted that only "late" strokes, namely, events occurring after discharge from the valve operation, were recorded. The STS guidelines were thus not followed with regard to also recording events during the early in-hospital phase. This is a minor problem, but it fortifies the impression that the present embolic stroke rates (1.3% to 2.3% per patient-year)—the main topic of the paper—are surprisingly high. In large long-term series with aortic bileaflet disk valves, the total rate of embolism was typically 1.0% to 1.5% per patient-year with approximately half of the events being strokes (ie, 0.5% to 0.75% per patient-year) [1]. In such series, most patients were maintained on "old-fashioned" intensity of anticoagulation with target INR greater than 2.5, and only a minor fraction of follow-up overlapped with the latter half of the 1990s when target INR tended to be lowered [1]. The bleeding rates reflected the target INR and were typically around 2.0% per patient-year but with only some 20% of events being cerebral [1].
"Modern" target INRs, for example, 2.0 to 3.0 for bileaflet disk valves in the aortic position, were used throughout the long follow-up period of the present paper, however, and the anticoagulant-related bleeding rates (all bleeds, not just cerebral) were correspondingly low. Such target INR may thus be the likely explanation of this paper's relatively high embolic stroke rates. One might speculate that lowering of target INR with the resulting lowering of the bleeding rate (20% stroke) actually buys a higher rate of a more malignant complication, namely thromboembolism (50% stroke). The INR targets of this paper together with the problems mentioned earlier indicates that present results cannot be compared with the those of most previous reports. However, the present results are probably important with regard to current decision making, choice of prosthetic valve (and target INR), indeed because of the very long follow-up with contemporary INR targets.
There is no significant news in the paper regarding identified risk factors, including the impact of smoking. Variations in the composition of patient materials and in the definition and registration of variables may explain why some risk factors appear in some and not in other analyses of embolism after valve replacement. I, finally, do not agree with the idea that a higher embolic stroke rate with mechanical than bioprosthetic valves in the mitral as opposed to the aortic position has a hemodynamic explanation. Patients who receive a bioprosthesis are older than patients who get a mechanical valve, and the prevalence of atrial fibrillation associated with mitral valve disease is highest among the oldest patients. Atrial fibrillation did not enter the multivariable risk model for the mitral valve group but valve type did. I suspect that there is considerable overlap between bioprosthesis and atrial fibrillation, and also with age, which may be equally important as the dichotomized age variable in the model was cut quite high (at 75 years). Patients with aortic valve disease, on the other hand, have very low prevalences of atrial fibrillation, and the similar stroke rates of (younger) mechanical and (older) bioprosthetic valve patients may simply reflect an age-related higher "background" stroke rate in the elderly, also from arterial thrombosis, which cannot be distinguished from an embolic stroke by computed tomography scanning.
References
This article has been cited by other articles:
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  F. Mellert, D. Bimmel, and C. J. Preusse Abnormal coiling of a pacemaker lead into the pulmonary artery with massive infectious thrombosis Europace, October 1, 2007; 9(10): 904 - 905. [Full Text] [PDF]
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 M. Ruel, V. Chan, P. Bedard, A. Kulik, L. Ressler, B. K. Lam, F. D. Rubens, W. Goldstein, P. J. Hendry, R. G. Masters, et al. Very Long-Term Survival Implications of Heart Valve Replacement With Tissue Versus Mechanical Prostheses in Adults <60 Years of Age Circulation, September 11, 2007; 116(11_suppl): I-294 - I-300. [Abstract] [Full Text] [PDF]
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M. Ruel, V. Kapila, J. Price, A. Kulik, I. G. Burwash, and T. G. Mesana Natural History and Predictors of Outcome in Patients With Concomitant Functional Mitral Regurgitation at the Time of Aortic Valve Replacement Circulation, July 4, 2006; 114(1_suppl): I-541 - I-546. [Abstract] [Full Text] [PDF]
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