“These results, while showing the validity of the different protocols for predicting mortality, can help form the basis for protocol recalibration to improve individual accuracy as well as comparability,” he says. Variability among the protocols in this regard could contribute to the observed variations in hazard ratios.ĭespite these limitations, this study drew on the largest cohort of stress tests using non-Bruce protocols to date to reveal previously unknown findings with important implications, Dr. Most importantly, the authors note, the results may reflect an inherent weakness in metabolic exercise stress testing - specifically, limitations in how accurately estimated METs reflect exercise ability compared with peak VO 2 measurements. Moreover, electrocardiographic and imaging data could shed light on differences in patient populations among the protocols but were not included in multivariable adjustments. This may have skewed referral patterns towards less healthy patients undergoing non-Bruce protocols. Although median patient age generally remained stable over that time, the number of patients referred for pharmacological testing increased over the study period. The authors also point out that the 25-year duration of the study period may have introduced bias. This theory is supported by the likelihood that patients with heart failure were more often tested with the Naughton protocol than the Bruce protocol, for historical reasons. Bhat, a Cleveland Clinic staff cardiologist. “It’s possible that factors not captured in the data registry - such as frailty or features of impairment assessed at bedside - may have been more common in patients referred for a non-Bruce protocol,” notes Dr. Over mean follow-up of 8.7 years, 8,426 patients died (6.9%).Īdvertising Policy Why do protocol results differ?Īn interesting finding, adds study co-author Pavan Bhat, MD, is that the non-Bruce protocols were associated with higher hazard ratios compared with the Bruce protocol despite robust risk factor adjustment. Data on deaths were obtained through June 10, 2016, from the Social Security Death Index and patient charts. The primary outcome was all-cause mortality. The following exercise stress protocols were represented: The analyzed cohort consisted of 120,705 patients (mean age, 53.3 ± 12.5 years 59% men). Data from patients who were referred for or converted to pharmacological testing were excluded. For patients with repeat tests, only the first results were used. This study included exercise stress test records of patients who underwent testing at Cleveland Clinic from January 1991 through February 2015. Furthermore, whether estimated METs obtained from different protocols are comparable has not been previously studied. However, limited data are available on the prognostic value of the alternative tests. While the Bruce exercise stress test has been well validated for predicting mortality, other options are frequently used instead, particularly for patients with physical limitations that necessitate testing with a less demanding protocol. “However, not all stress tests are alike, so a patient’s MET values from consecutive exercise stress tests provide comparable information only if the same protocol was used.” Multiple choices for exercise stress testing

“Lower exercise capacity is associated with higher death rates regardless of which protocol is used,” says the study’s senior study author, Wael Jaber, MD, a Cleveland Clinic staff cardiologist.

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