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J Thorac Cardiovasc Surg 2003;126:2117-2118
© 2003 The American Association for Thoracic Surgery
Letter to the editor |
Department of Surgery, University of Illinois at Chicago, Chicago, IL 60612, USA
To the Editor:
The article by David and colleagues1 in the May 2003 issue of the Journal, "Late Outcomes of Mitral Valve Repair for Floppy Valves: Implications for Asymptomatic Patients," stirs important unanswered questions and concerns. The conclusion that patients with asymptomatic mitral valve in- competence are candidates for surgery might be extrapolative yet beneficial—if it had stemmed from a different study design. In statistical terms, significance for operating was clearly established; however, this was more rhetorical than useful in clinical practice. The following issues were not mentioned in the discussion or among the discussants.
First, asymptomatic simply means no symptoms. Mitral valve surgery is feasible, but its benefits to the individual patient cannot be observed here because of the confounding variables in the methodology and results. To the reader, the concept of cause and effect is paramount to executing successful cardiovascular epidemiology. Whereas the scientific sequence of cause and effect is clear, the application of such a valid concept in this article leans to the reverse order. In other words, because surgery in patients without symptoms had a low morbidity and mortality (cause), it is recommended to operate for asymptomatic mitral incompetence (effect). Lowering the threshold to operate must stem from convincing data, and even if statistically significant the clinical indication is neither relative nor absolute. The patient's physiologic status must the underlying cause for an operation, and the outcome of the operation (effect) must treat that cause. In this article despite the effect being feasible, the cause is far from a true clinical indication. The practicing surgeon can be confused with the paradigm of cause and effect that appears to argue that the mortality is higher among patients with symptoms. Drawing feasibility from such a statistic may introduce a new "fuzzy logic" dimension that has no order and no cause followed by effect features.2 This logic results from many decision-making and problem-solving tasks that are too complex to be understood quantitatively; however, people succeed by using knowledge that is imprecise rather than precise.
Second, it is interesting that absolute risk reduction in mortality from 23% to 6% is 17% in those symptom-free patients who were operated on. However, all variables in a scientific study must be controlled except the single variable that is being studied. Thus, when David and colleagues1 attempted to modify a successful operative procedure, underlying background pathologies in the control and study groups needed to be similar. This was lacking.
Third, the demographic data (Table1 in the original article1) reveal an important cause with regard to the population sample. Atrial fibrillation (AF) was more prevalent in the symptomatic than asymptomatic group (P = .0001). Chronic AF carries greater risk than intermittent AF, doubling the risk of cardiovascular mortality. In other words, implications for symptom-free patients are only indirectly related, as opposed to a direct cause-effect relationship with AF.3 Moreover, diabetes mellitus in the symptomatic group approached a statistically significant difference (P = .07). More recently, it has been shown that all the patients with insulin-dependent diabetes mellitus with left diastolic dysfunction have evidence of definitive autonomic neuropathy. Such isolated diastolic dysfunction may be the principal physiologic mechanism in these patients. The annual mortality from diastolic heart failure varies widely, from 9% to 28%,4 This variable should be addressed in the context of patient cohort by reviewing echocardiographic evidence of diastolic dysfunction. The mortality rate among patients with diastolic heart failure is 4 times that among persons without heart failure but half that among patients with systolic heart failure.
Third, apart from the semantics of asymptomatic, of more interest at mean follow-up 93% of patients in the asymptomatic group were in New York Heart Association (NYHA) functional class I or II, which was not statistically significant from the symptomatic group (88%). This result argues that mitral valve surgery repair on symptom-free patients does not confer any further clinical benefit. This statistic is consistent with others and follows classic teachings. Also, the discrepancy between the reoperation rate and the incidence of significant mitral valve regurgitation indicates that not all patients having important valve incompetence late after repair undergo surgery again within the time frame. This repeated observation creates a new argument that recurrent mitral incompetence lacks substance as an indication for operation and argues against the primary hypothesis and conclusion of David and colleagues.1
Fourth, David and colleagues1 did not mention the well-known limitations to the simple NYHA scale for cardiovascular disability. NYHA has a tendency to oversimplify an issue or a problem by ignoring complexities or complications. The criteria committee of the NYHA has provided a widely used classification that relates symptoms to "ordinary" activity. The term ordinary is subject to various interpretations, as are terms such as undue fatigue. Such terms have limited the accuracy and reproducibility of the NYHA classification.5
In the end, it is desirable to seek patients who need an operation. Offering such surgery to symptom-free patients on the basis of effect rather than cause, however, is simplistic and fuzzy. Better data analytic methodology and study design are needed to qualify for a new indication.
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