Exercise Capacity and Risk

Women's capacity for exercise has been shown to be an independent predictor of mortality.^67-69 In a study of 5721 asymptomatic women⁶⁷:

• Metabolic equivalent (MET) levels <5 were associated with a 3.1-fold increase in the risk of death compared to levels >8.
• MET levels of 5 to 8 were associated with a 1.9-fold increase in the risk of death compared to levels >8.
• Every 1-MET increase in exercise capacity resulted in a 17% decrease in mortality risk.

In another study, women who failed to achieve ≥85% of their predicted maximal heart rate had a 5-year event-free survival rate of 52%, compared with 77% for women who were able to reach an adequate heart rate (P = .005).⁷⁰

Click on a link below for more information:

• Nomogram for Calculating Exercise Capacity
• Risk Prediction
• Duke Activity Status Index (DASI) Scores for Pre-testing Risk Stratification

Nomogram for Calculating Exercise Capacity

Until recently, normative values of exercise capacity for age in women had not been established, making the extrapolation of risk from predicted and actual exercise levels more challenging.⁶⁸ In 2005, a new nomogram was introduced that can be used to calculate the percentage of a woman's age-predicted exercise capacity that she is actually able to reach (Figure 8).⁶⁸ Draw a line from the patient's age (left-side scale) to the MET level achieved (right-side scale). The point at which your line crosses the diagonal line on the chart shows the patient's percentage of age-predicted exercise capacity reached.

Figure 8. Nomogram for Calculating the Percentage of Women's Age-Predicted Exercise Capacity Attained ⁶⁸

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Risk Prediction

Based on the nomogram above, the risk of cardiac death among symptomatic women whose actual exercise capacity was <85% of their age-predicted capacity is twice that of women whose actual capacity is ≥85% of their age-predicted value.⁶⁸ In asymptomatic women, the risk of cardiac death was 2.44 times higher for those unable to reach 85% of their age-predicted value.⁶⁸ Incorporating this nomogram into the interpretation of exercise stress testing can provide additional information that can be used for risk stratification and to determine if additional diagnostic testing is required.

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DASI Scores for Pre-testing Risk Stratification

According to WISE* study results, low functional capacity in women with suspected myocardial ischemia, as estimated by the DASI, correlates with indeterminate exercise test results and is associated with an adverse prognosis.⁷⁰ The DASI is a simple, self-administered, 12-item quality-of-life instrument that records a patient's self-assessment of her functional abilities.⁷⁰

The WISE findings included⁷⁰:

• 37% of women with an estimated capacity of ≤4.7 METs were unable to reach predicted maximal heart rate, compared with 6% of those with an estimated capacity of >4.7 METs.
• Exercise testing results were indeterminate (ie, <85% predicted maximal heart rate) in 37% of women scoring ≤4.7 METs but in only 6% of those scoring >4.7 METs (P = .001).
• Similar results were obtained using cutoffs of 6 and 3 METs (P = .021 and .001, respectively).
• Exercise-induced ischemia occurred in 39% of women scoring ≤4.7 METs and in 64% of those scoring >4.7 METs (P < .0001).
• At 5-year follow-up:
• 67% of cardiac deaths or nonfatal MIs occurred in women scoring ≤4.7 METs (P = .003).
• Event-free survival significantly correlated with DASI-estimated METs (P = .009) (Table 3).

Table 3. Correlation of Functional Ability and 5-Year Event-Free Survival ⁷⁰

DASI-Estimated METs	Event-Free Survival
>9.9	95%
7.5-9.9	92%
4.8-7.4	88%
1-4.7	83%

Based on these WISE study results, the use of the DASI before exercise testing can risk-stratify symptomatic women and would help identify higher-risk, functionally impaired patients who may benefit from targeted risk management.⁷⁰

*WISE = Women's Ischemic Syndrome Evaluation.

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