In Reply:-We thank Drs. Litwack and De Grutolla for their interest in our manuscript investigating postoperative myocardial infarction (PMI) after noncardiac surgery. As indicated, they would have preferred the use of multivariable statistical models in our data analysis. To answer their questions regarding change in heart rate and opioid use and the relative contributions of demographics, we performed a stepwise logistic regression using the variables listed in Table 2 and Table 3 of our original manuscript and postoperative change in heart rate. The main results are shown in the table. One can see that age and nitrate usage again were significantly linked with PMI. Change in heart rate on postoperative day 4 was determined to be a risk factor for PMI. Interestingly, hypotension in the postanesthetic care unit was the most significant risk factor for PMI. The decreased narcotic requirements in PMI patients again were not a significant risk factor. As indicated in our manuscript, we cannot determine whether the heart rate changes were the cause or the result of the PMI because of our lack of continuous heart rate recording. Similarly, postanesthetic care unit hypotension may have been an early clinical sign of the developing PMI and not a causative event because our enzyme assays were not performed before postanesthetic care unit arrival.
We cannot answer their question regarding the definition of MI and subsequent events because we did not, nor do we, have the ability to determine the occurrence of all non-MI deaths that occurred. Lastly, we would be happy to share our database, as suggested, to enable the development and validation of risk profiles for MI and other surgical outcomes with appropriate investigators.
Neal H. Badner, M.D., F.R.C.P.C.
Adrian W. Gelb
Professor and Chair; Department of Anaesthesia; Faculty of Medicine; University of Western Ontario; London, Ontario, Canada;email@example.com
(Accepted for publication July 7, 1998.)