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J Thorac Cardiovasc Surg 2003;126:1668-1670
© 2003 The American Association for Thoracic Surgery
Letters to the editor |
a Department of Cardiology, Heart Center North Rhine-Westphalia, Ruhr University Bochum, Bad Oeynhausen, Germany
To the Editor:
In a recent issue of this Journal, Grunkemeier and Wu1 analyzed complication rates after bileaflet valve implantation by means of pooled data and regression analysis. Their criticism regarding inappropriate comparison of complication rates for different valve prostheses is more than justified. They approached the problem as a meta-analysis, although the exact criteria and methodology were not well documented.
Valid comparison of results with different heart valve substitutes is restricted to controlled, randomized studies. If randomized studies are not available, results of nonrandomized studies may be used to answer clinical questions. However, one should be extremely careful not to misuse and misinterpret the data analyzed. The article to which we are responding is a potential example of misuse and misinterpretation of data taken from the literature, including the data set of my own group.2 The article has at least four major shortcomings: (1) inconsistent use of linearized rates, (2) inclusion violations, (3) inadequate reflection of follow-up techniques, and (4) publication bias.
First, in terms of inconsistent use of linearized rates, for their analysis Grunkemeier and Wu1 appear to have included the early postoperative follow-up period in the linearized complication rates per patient year. However, it is not clear whether this rule was consistently applied. This can lead to misleading results because of the elevated and nonlinear rates for both bleeding and thromboembolic complications in the early postoperative period.3
Second, the study exhibits severe violations of its own inclusion criteria. For well-considered reasons, the study results published by our group and included in the regression analysis were explicitly not based on the American Association for Thoracic Surgery and Society of Thoracic Surgeons guidelines for reporting valve-related morbidity and mortality. Instead, we used a modified Karnofsky scale, which does not correspond to these guidelines. This scale, adapted by us to the special requirements for the long-term follow-up after valve replacement, allowed grading of reported complications2,4 and reporting of minor bleeding complications. Lack of differentiation between the two reporting systems resulted in severe violation of study inclusion criteria.
Third, a major problem when analyzing pooled data is invalid reporting of complications as a result of inappropriate follow-up techniques.5 The guidelines for reporting morbidity and mortality used in the data sets selected by Grunkemeier and Wu require reporting of all complications occurring during follow-up. The completeness of reporting is directly related to the follow-up strategies, such as the time intervals between consecutive follow-up examinations and how the data are gathered.5 Reliable follow-up data that include information on transient and reversible events are most effectively collected with regular follow-up visits to a specialized outpatient clinic or by on-line documentation, a strategy first used by my group.2 Indeed, studies have shown that when, parallel to the regular follow-up in the outpatient department, the same patients were sent questionnaires at 6-, 18-, and 36-month intervals, about half of the events that were transient or reversible had been forgotten and therefore were not mentioned on the 18- and 36-month questionnaires.5,6 Incomplete data reporting may be illustrated further by the following. Of the 21 studies giving full information with regard to bleeding and thromboembolism, 4 reported linearized rates after aortic valve implantation below the background incidence for the combined end point of thromboembolism plus bleeding, indicating that proper follow-up techniques were lacking because not even the background incidence of such complications in the age-adapted general population was detected.
Finally, some of the studies included in the analysis represent atypical situations. One example is the series published by Baudet,7 who had patients during the first postoperative year on antiplatelet medication only. This series contributed 23 of the 82 valve thromboses (28%, 0.29%/patient-y) of the St Jude Medical data pool, compared with an average of 0.13%/patient-y for all other series. One must not include such an experimental series in the analysis of pooled data, because it can lead to arbitrary and unreliable conclusions.
To conclude, there are three messages that may come from the article that I criticize here. First, we need refined criteria for reporting morbidity and mortality after valve replacement. Cerebral events of unknown etiology should no longer be counted as thromboembolism, because most such patients have cerebral bleeding, not embolism, when cerebral computed tomographic scans are performed. Simple counting of complications is inappropriate, because the vast majority of bleeding complications documented during appropriate follow-up have neither a prognostic impact nor do they influence quality of life. Reporting of morbidity should go along with grading the severity of the respective complications, as suggested earlier.2
Second, for each study it must be clear which patients have been included. For consecutive patients not only the postoperative survivors should be considered but all patients who underwent surgery (intent-to-treat analysis). An inept surgeon with a high intraoperative mortality would in effect eliminate many patients who would have to be considered at high risk for postoperative complications.
Third, in the era of evidence-based medicine the cardiovascular community should develop guidelines for the follow-up of patients. A careless cardiologist unwilling or unable to document potential complications because of inappropriate follow-up techniques will end up with the best results (and the combination of an inept surgeon and a careless cardiologist will always produce the best results). That may be the true impact of this article. With regard to follow-up, the message should be that it is the careful follow-up documentation of all complications that ensures the quality of the study. Sophisticated statistical techniques, no matter how elegant, cannot make up for deficiencies in this area.
References
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