Submaximal target heart rate and the detection of myocardial ischemia by stress myocardial perfusion imaging using the treadmill exercise Bruce protocol

Objective: It has been postulated that if patients fail to achieve their age-predicted target heart rate (THR: 85% of predicted maximal HR), the electrocardiographic changes following exercise treadmill test (ETT) and also scintigraphic results of this stress protocol for myocardial perfusion imaging (MPI) are unreliable. We decided to assess the ability of submaximal ETT in provoking ischemia as determined by MPI. Methods: One hundred and nine patients (60 female, 49 male, mean age: 50.8±11.4, range: 32-76 years), were prospectively assessed with MPI after stress protocol of ETT. Forty-nine patients failed to attain THR. Myocardial perfusion imaging was performed based on the 1-day protocol, using Technetium-99m sestamibi (99mTc-MIBI). Results: Sixty patients attained THR, of which 28 patients (46.7%) had normal myocardial perfusion pattern and 32 patients (53.3%) had scintigraphic evidence of ischemia. The remaining 49 patients had submaximal ETT, of which 15 patients (30.6%) had normal results and 34 patients (69.4%) had scintigraphic evidence of ischemia. Although ischemia was more common in those patients with submaximal ETT, however the difference was not statistically significant (p=0.088). Conclusion: Ischemia is more common in patients who had performed a sub-maximal ETT. It could be a logical hypothesis that ischemic heart disease may limit the ability of patients to complete ETT and therefore, it would not be judged that submaximal ETT is always insufficient for MPI. In these settings, in patients who fail to attain the THR, it would be possible to proceed to the stress MPI test.