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Comparative Study
. 2009 Aug 4;54(6):538-45.
doi: 10.1016/j.jacc.2009.04.042.

Achieving an exercise workload of > or = 10 metabolic equivalents predicts a very low risk of inducible ischemia: does myocardial perfusion imaging have a role?

Jamieson M Bourque  1 , Benjamin H Holland, Denny D Watson, George A Beller
Affiliations
Comparative Study

Achieving an exercise workload of > or = 10 metabolic equivalents predicts a very low risk of inducible ischemia: does myocardial perfusion imaging have a role?

Jamieson M Bourque et al. J Am Coll Cardiol. .

Abstract

Objectives: We sought to identify prospectively the prevalence of significant ischemia (> or =10% of the left ventricle [LV]) on exercise single-photon emission computed tomography (SPECT) imaging relative to workload achieved in consecutive patients referred for myocardial perfusion imaging (MPI).

Background: High exercise capacity is a strong predictor of a good prognosis, and the role of MPI in patients achieving high workloads is questionable.

Methods: Prospective analysis was performed on 1,056 consecutive patients who underwent quantitative exercise gated (99m)Tc-SPECT MPI, of whom 974 attained > or =85% of their maximum age-predicted heart rate. These patients were further divided on the basis of attained exercise workload (<7, 7 to 9, or > or =10 metabolic equivalents [METs]) and were compared for exercise test and imaging outcomes, particularly the prevalence of > or =10% LV ischemia. Individuals reaching > or =10 METs but <85% maximum age-predicted heart rate were also assessed.

Results: Of these 974 subjects, 473 (48.6%) achieved > or =10 METs. This subgroup had a very low prevalence of significant ischemia (2 of 473, 0.4%). Those attaining <7 METs had an 18-fold higher prevalence (7.1%, p < 0.001). Of the 430 patients reaching > or =10 METs without exercise ST-segment depression, none had > or =10% LV ischemia. In contrast, the prevalence of > or =10% LV ischemia was highest in the patients achieving <10 METs with ST-segment depression (14 of 70, 19.4%).

Conclusions: In this referral cohort of patients with an intermediate-to-high clinical risk of coronary artery disease, achieving > or =10 METs with no ischemic ST-segment depression was associated with a 0% prevalence of significant ischemia. Elimination of MPI in such patients, who represented 31% (430 of 1,396) of all patients undergoing exercise SPECT in this laboratory, could provide substantial cost-savings.

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Figures

Figure 1
Figure 1
Study cohort derivation flowchart.
Figure 2
Figure 2. Prevalence of left-ventricular ischemia by exercise capacity
The 974 individuals reaching 85% of their MAPHR were divided by exercise workload achieved (horizontal axis). The vertical axis represents the percentage of subjects with each percentage of LV ischemia.
Figure 3
Figure 3. Relationship of ischemic ST-Depression on the exercise ECG and workload achieved to the percentage of LV ischemia
The 974 subjects reaching ≥85% of their MAPHR were divided by the exercise workload attained and the presence of ischemic ST-depression. The vertical axis represents the prevalences of 5-9% and ≥10% LV ischemia.
See this image and copyright information in PMC

Comment in

  • Customized exercise testing.
    Wackers FJ. Wackers FJ. J Am Coll Cardiol. 2009 Aug 4;54(6):546-8. doi: 10.1016/j.jacc.2009.04.044. J Am Coll Cardiol. 2009. PMID: 19643317 No abstract available.
  • Value of a high exercise workload to rule out myocardial ischemia.
    Bouzas-Mosquera A, Peteiro J, Alvarez-García N. Bouzas-Mosquera A, et al. J Am Coll Cardiol. 2010 Jan 19;55(3):265-6; author reply 266-7. doi: 10.1016/j.jacc.2009.08.054. J Am Coll Cardiol. 2010. PMID: 20117421 No abstract available.

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