Patients who undergo preoperative echocardiography before surgery die slightly more often in the months following noncardiac surgery, according to a study in the British Medical Journal.
Among more than 200,000 patients in the cohort, preoperative echo was associated with a small increase in mortality at several time points starting at 30 days postsurgery, said the research team from Toronto and the University of Pennsylvania in Philadelphia, which emphasized that the association does not imply a causal link. Patients who underwent echocardiography may have been sicker, they said. And those who had a stress test as well as echo saw no increase in risk, noted Dr. Duminda Wijeysundera from Toronto's Keenan Research Center and colleagues.
"The increase in mortality varied according to whether patients had clinical risk factors for perioperative cardiac events or had had noninvasive stress testing," Wijeysundera et al wrote (BMJ, 30 June 2011).
"Cardiac complications occur after at least 2% of elective noncardiac procedures and account for a third of postoperative deaths," the authors noted. Clinicians often use specialized cardiac tests to improve their preoperative risk estimates, and resting echocardiography is the most frequently ordered test before major noncardiac surgery, the authors wrote.
Echo offers several advantages because it requires no contrast media, radioactive isotopes, or radiation exposure. It provides information on ventricular dysfunction and valvular abnormalities, and fixed wall motion abnormalities that suggest previous myocardial infarction. However, some authors have suggested that information derived from echocardiography does not provide additional prognostic information when combined with readily available clinical risk factors.
"No randomized controlled trial has yet evaluated the effect of preoperative echocardiography on postoperative outcomes," they noted. "We therefore did a population based cohort study in Ontario, Canada, to determine whether echocardiography before elective intermediate- to high-risk noncardiac surgery was associated with improved survival and shorter hospital stay."
Using several government databases, the study examined the records of all Ontario residents 40 years and older who underwent one of several noncardiac surgeries between 1999 and 2008. The study focused on higher-risk procedures including abdominal aortic aneurysm repair, car endarterectomy, peripheral vascular bypass, total hip replacement, total knee replacement, large bowel resection, partial liver resection, Whipple procedure, pneumonectomy, pulmonary lobectomy, gastrectomy, esophagectomy, nephrectomy, and cystectomy.
Of the 264, 823 patients in the entire cohort, approximately 15% (n = 40,084) had either transthoracic or transesophageal echocardiography within 180 days before surgery on an outpatient basis.
"We used a one-year follow-up period to ascertain mortality because postoperative cardiac complications are not well captured by administrative databases but are closely associated with increased long-term mortality," the authors wrote. Analysis of outcomes was limited to outpatient echo due to the difficulty of tracking inpatient procedures.
Propensity score methods were used to create a matched cohort (n = 70,996) that reduced the differences between patients with and without presurgical echocardiography. The matched cohort showed small but statistically significant increase in mortality among patients who had undergone echocardiography.
Even with the matched cohort, echocardiography before noncardiac surgery was associated with increases in 30-day mortality (relative risk [RR] 1.14, 95% confidence interval [CI] 1.02 to 1.27), one-year mortality (RR 1.07, 1.01 to 1.12), and length of hospital stay (RR 0.31, 95% CI 0.17 to 0.44) days; but there was no difference in surgical site infections (1.03, 0.98 to 1.06), the group reported. However, the association with mortality was influenced (p = 0.02) by whether patients had had stress testing or had risk factors for cardiac complications.
"Those who had echocardiography were generally older men who had greater burdens of comorbid disease; they were more likely to have had specialist consultations and cardiac stress testing," Wijeysundera and colleagues wrote. "Additionally, they were more likely to receive epidural anesthesia and intraoperative invasive monitoring."
Patients who had echocardiography were also more likely to have received new prescriptions for beta-blockers, statins, angiotensin converting enzyme inhibitors, and angiotensin receptor blockers before surgery. Both groups had similar rates of coronary angiography or coronary artery bypass grafting before surgery and lower rates of percutaneous coronary intervention.
"Preoperative echocardiography was frequently ordered and was associated with statistically significant, but very small, increases in mortality and length of hospital stay after major elective noncardiac surgery," the study team stated, adding that the increase in mortality varied according to the patient's clinical risk factors for cardiac events.
"Echocardiography was not associated with any difference in mortality among patients who also had stress testing or among patients at high risk with three or more clinical risk factors," they wrote. "However, it was associated with increased mortality among patients at low to intermediate risk who had not had stress testing." The mortality increases in these subgroups were "mirrored by qualitatively similar increases in perioperative beta-blockade," they added.
"By comparison, cardiac stress testing is associated with decreased survival in patients at low risk but with improved survival in those at intermediate to high risk," Wijeysundera and colleagues wrote. And stress echocardiography accurately stratifies perioperative cardiac risk and is associated with better outcomes in certain subgroups of patients. Unknown factors were potentially confounding.
"Patients who had echocardiography may have been sicker and therefore at increased risk for postoperative complications," they noted. "Despite our use of statistical methods to adjust for these differences and excellent covariate balance within the matched pairs, our data sources may have lacked sufficient detail to allow adequate adjustment for risk." Any residual confounding was likely small, however, and unlikely to have masked the benefits of preoperative echocardiography.
Importantly, these findings apply to resting echocardiography, not stress echocardiography, which accurately stratifies perioperative cardiac risk and is associated with improved outcomes in certain subgroups, they noted.
The authors cited several possible reasons for the results, noting for example, that although echocardiography can identify systolic dysfunction, the information has relatively poor prognostic accuracy -- and that ejection fractions derived from echocardiography did not accurately stratify cardiac risk. Even when preoperative echocardiography identifies ventricular dysfunction, there is no proven treatment to reduce the associated perioperative risks.
Second, they said, echocardiography is poorly suited to stratifying risk attributable to coronary artery disease.
"It does identify fixed wall motion abnormalities that suggest previous myocardial infarction," Wijeysundera and colleagues wrote. "However, in the absence of inducible ischemia, which is instead identified by stress testing, fixed defects are not associated with increased perioperative risk. The inability of resting echocardiography to identify inducible ischemia also limits its capacity to help to target perioperative beta-blockade, which has its best risk-benefit profile in people with inducible ischemia."
Finally, echo was associated with an increased risk of beta-blockade, which may help explain the increased mortality in these same subgroups, the authors stated.
The authors emphasized that an observational study does not "prove a causal link between echocardiography and postoperative mortality," especially since the data sources "did not capture detailed clinical characteristics. The findings warrant confirmation using other multicenter studies and different data sources, including a randomized trial of routine preoperative echocardiography," they wrote.
"Overall, using preoperative echocardiography for specific diagnostic indications is reasonable; however, our results would suggest that, in the absence of such indications, echocardiography does not provide clinically useful information to improve perioperative care, Wijeysundera and colleagues concluded.