tailieunhanh - NEJM CARDIOVASCULAR DISEASE ARTICLES - Part 9

bệnh nhân được xác định bởi các bác sĩ giới thiệu), và sự khác biệt trong các biến được sử dụng để phân tích xu hướng, chẳng hạn như thu nhận của các đồng biến số dựa trên cơ tim, tưới máu SPECT phản ánh tỷ lệ phần trăm của cơ tim thiếu máu cục bộ và sẹo. | dyspnea and cardiac prognosis patient or identified by the referring physician and differences in the variables used for propensity analysis such as our inclusion of covariates based on myocardial-perfusion SPECT that reflect the percentage of ischemic and scarred myocardium. In addition experience has demonstrated that differences in pretest referral biases . differences in the clinical characteristics ofreferral populations 24 25 can markedly influence the perceived prognostic accuracy of clinical variables among studies. Accordingly there is a need to assess the extent to which the prognostic significance of dyspnea is influenced by pretest referral bias across various patient populations. Our study has a number of limitations. Ventricular function was not assessed in all the patients since gated myocardial-perfusion SPECT required for its assessment was not routinely performed until 1995. We used only a single dichotomous question concerning dyspnea which did not grade the severity or precipitants of the symptom. By comparison the American Thoracic Society uses a five-point scale for Paradoxically this limitation underscores the strength of our data since dichotomously evaluated test variables generally convey less inherent information than variables that are classified in more Since we only coded dyspnea among patients without chest pain we could not evaluate the potential interaction between dyspnea and symptoms of chest pain. We also did not evaluate the reproducibility of the self-reported symptoms. Historical or testing information regarding lung disease would have been useful. In addition since our study patients represent a referral population for myocardial-perfusion SPECT caution should be exercised in extrapolating our findings to the general population. The most important limitation of our study is that because dyspnea is closely associated with a variety ofboth cardiovascular and noncardiovascu-lar disorders it may not have .