Circulation, Vol 87, 815-830, Copyright © 1993 by American Heart Association
RE Kuntz, KM Keaney, C Senerchia and DS Baim
BACKGROUND. Investigations of coronary restenosis typically use late (4-
6-month) angiographic end points. Since only 50-80% of patients generally
undergo repeat angiography, however, restenosis for the population as a
whole is usually estimated by assuming that nonrestudied and restudied
patients are similar. If restudied and nonrestudied patients differ,
incomplete angiographic follow-up can yield an erroneous estimate of
restenosis. No suitable method has yet been devised to detect and correct
these errors. METHODS AND RESULTS. We studied the clinical indications for
angiographic restudy in an actual series of 301 treated lesions in 267
consecutive patients who underwent either Palmaz-Schatz stenting (126
patients) or directional coronary atherectomy (141 patients) at our
institution. While only 249 (83%) treated segments underwent 4-6-month
angiographic follow-up, all had clinical follow-up that described whether
specific indications for restudy were present. Patients who had no clinical
indications for such restudy were designated as having elective follow-up.
In contrast, patients who had recurrent symptoms or positive exercise
studies and were scheduled for repeat angiography at the independent
recommendation of their referring cardiologist were designated as having
nonelective follow-up. Mean late percent stenosis or binary restenosis rate
(> 50% diameter stenosis) was determined for elective versus nonelective
lesions that underwent follow-up angiography. These values were then used
to input the behavior of the nonrestudied lesions according to their
clinical status. From these imputations, a "predictive" model was developed
to estimate the mean restenosis values that would have been found had the
entire population actually undergone angiographic follow- up. Comparisons
between the estimates of this predictive method and the traditional method
that uses only the actual angiographic data demonstrate how alterations in
various parameters influence the selection bias caused by incomplete
angiographic follow-up. Of the 301 lesions available for follow-up, 100 of
the 103 (97%) nonelective versus 149 of the 198 (75%, p < 0.001)
elective lesions actually underwent angiographic follow-up. Mean follow-up
percent stenosis (50% versus 27%) and the binary restenosis rate (53%
versus 13%) differed significantly for the nonelective versus the elective
lesions, respectively (both p < 0.001). Even at the fairly high (83%)
angiographic follow-up rate, elective versus nonelective status was thus a
confounder that caused differences between the restenosis rate estimated by
the traditional (29.1%; 95% CI: 23.4, 34.7) and the predictive methods
(26.3%; 95% CI: 21.4, 31.1). Larger (and even statistically significant)
differences may be present under the conditions that exist in many current
studies. CONCLUSIONS. Restenosis trials with < 90% angiographic
follow-up suffer from selection bias. Traditional methods that analyze only
the restudied patients fail to correct for the important confounding
influence of the clinical status of the nonrestudied patients. By using
this readily available clinical information about the nonrestudied
patients, a predictive method may be developed that provides a closer
estimate of the true restenosis behavior for the population as a whole.
ARTICLES
A predictive method for estimating the late angiographic results of coronary intervention despite incomplete ascertainment
Charles A. Dana Research Institute, Boston, MA.
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