CORRESPONDENCE: LETTER TO THE EDITOR
Reply
Jamieson Bourque, MD*
* Cardiovascular Division, Department of Internal Medicine, University of Virginia Health System, P.O. Box 800662, 1215 Lee Street, Charlottesville, Virginia 22908 (Email: jamieson2{at}gmail.com).
We thank Dr. Bouzas-Mosquera and colleagues for their comments regarding our paper (1). They report the prevalence of ischemic wall-motion abnormalities by stress echocardiography in 2 studies that seem to have fundamental differences compared with ours (2,3). One important distinction is the variation in study cohort clinical characteristics. They analyzed 1 group of 1,433 patients with high exercise capacity and a 30% rate of stress-induced wall-motion abnormalities (3). Compared with our population, this cohort had a higher prevalence of previous myocardial infarction (29.0% vs. 11.8%) and included individuals with exercise ST-segment depression (14%) and achievement of <85% of their maximum age-predicted heart rate (19%). We excluded these types of patients from our low-risk cohort (1). Their inclusion in the analysis by Bouzas-Mosquera and colleagues likely contributed to the increased ischemia observed in their cohort. Moreover, they included women who reached only 8 metabolic equivalents (METs) of exercise workload compared with our cutoff of  10 METs for both men and women. This is an important difference because those patients in our study who achieved 7 to 9 METs of workload had a 10-fold increase in the prevalence of 10% left ventricular ischemia (4.3% vs. 0.4%).
The analysis of ischemia in our study was quantitative in nature. The qualitative (i.e., visual) approach used by Bouzas-Mosquera et al. (2) is associated with a higher rate of false positives for ischemia, especially in the setting of resting dysfunction, as seen in previous myocardial infarction.
To match our population more closely, Bouzas-Mosquera et al. (2) examined a second population reaching 10 METs and 85% of maximum age-predicted heart rate that expectedly had a lower prevalence of stress wall-motion abnormalities (15%) than in their other cohort (30%). It is unclear how many of these positive echocardiographic studies represent true ischemia versus false positivity because the echocardiographic results were not correlated with coronary angiography and no cardiac outcomes were provided. Thus, the 15% ischemia prevalence in this population was not validated against a gold standard and seems high for patients achieving a high workload. In our study, the rate of any ischemia in such patients was 4.0%, which is more in line with what is expected in individuals reaching high exercise workloads and target heart rate and with what has been described in previous reports. This suggests that a significant proportion of the stress wall-motion abnormalities in the study of Bouzas-Mosquera et al. (2) may have been falsely positive for ischemia. If there were in fact such a high rate of ischemia in their 10 METs cohort (15%), an increased event rate could be expected. Unfortunately, the survival data for this subgroup were not provided. Previous prognostic studies show low mortality rates in patients with high exercise capacity.
We agree with Dr. Bouzas-Mosquera and colleagues that additional research is necessary to confirm that the very low risk of significant ischemia in our population is associated with a comparably low rate of cardiac events. In fact, we performed a preliminary outcomes analysis of our cohort that showed no cardiac deaths over 1 year for subjects achieving 10 METs and 85% maximum age-predicted heart rate during exercise stress myocardial perfusion testing (4).
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1. Bourque JM, Holland BH, Watson DD, Beller GA. Achieving an exercise workload of 10 metabolic equivalents predicts a very low risk of inducible ischemia: does myocardial perfusion imaging have a role? J Am Coll Cardiol 2009;54:538-545.[Abstract/Free Full Text]2. Bouzas-Mosquera A, Peteiro J, Alvarez-Garcia N, et al. Prediction of mortality and major cardiac events by exercise echocardiography in patients with normal exercise electrocardiographic testing J Am Coll Cardiol 2009;53:1981-1990.[Abstract/Free Full Text] 3. Peteiro J, Monserrrat L, Bouzas B, Marinas J, Castro-Beiras A. Risk stratification by treadmill exercise echocardiography in patients with excellent exercise capacity Echocardiography 2007;24:385-392.[CrossRef][Web of Science][Medline] 4. Bourque JM, Charlton GT, Holland BH, Belyea CM, Watson DD, Beller GA. Low prevalence of ischemia and excellent prognosis in an intermediate-risk cohort achieving 10 METS on Exercise myocardial perfusion imaging: was SPECT imaging necessary (abstr)? Circulation 2009;120:S319.
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Value of a High Exercise Workload to Rule Out Myocardial Ischemia
- Alberto Bouzas-Mosquera, Jesús Peteiro, and Nemesio Álvarez-García
J. Am. Coll. Cardiol. 2010 55: 265-266.
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