MORONAPEDIA - Medical Encyclopedia

Impaired chronotropic response (CR) after exercise treadmill testing (ETT) is an effective, noninvasive tool to evaluate cardiac risk in patients with diabetes, according to the results of a study reported in the August issue of Diabetes Care.

“Impaired CR is defined as inability of the heart rate to increase normally with exercise and may be related to alterations in sympathetic and parasympathetic tone, as well as autonomic dysfunction,” write P. Michael Ho, MD, PhD, from the Denver Veterans Administration Medical Center in Colorado, and colleagues. “Impaired CR during…ETT is associated with increased risk of cardiac events and all-cause mortality. Patients with diabetes have a higher incidence of autonomic dysfunction, and therefore impaired CR during ETT may identify patients with diabetes at risk for adverse outcomes.”

The goal of this study was to evaluate the association between impaired CR and adverse events in diabetic patients who were referred for ETT. The independent association between impaired CR, defined as achievement of less than 80% of a patient’s heart rate reserve, and adverse outcomes was evaluated with multivariable Cox proportional hazards regression adjusting for demographics, comorbidities, and treadmill variables including the Duke Treadmill score.

During ETT, 479 (35.7%) of 1341 patients with diabetes had impaired CR. In these patients, risk for all-cause mortality, myocardial infarction, or coronary revascularization procedures was increased. Impaired CR remained significantly associated with adverse outcomes in multivariable analyses (hazard ratio, 1.53; 95% confidence interval, 1.10 - 2.14).

“Among patients with diabetes, impaired CR is common during ETT and is associated with adverse outcomes,” the study authors write. “Impaired CR can be used as another noninvasive tool to risk-stratify patients with diabetes following ETT….Additional studies are needed to determine whether the presence of impaired CR during ETT among patients with diabetes should lead to more aggressive medical therapy, additional noninvasive testing with imaging, or invasive evaluation.”

Clinical Context

Impaired CR is defined as the inability of the heart rate to increase normally with exercise. This inability may be related to alterations in the sympathetic and parasympathetic tone as well as autonomic dysfunction. It is well known that impaired CR during ETT is indicative of an increased risk for cardiac events and all-cause mortality. Diabetic patients usually have a higher incidence of autonomic dysfunction. It has been proposed that impaired CR during ETT may identify diabetic patients for adverse outcomes; however, previous studies have been inconclusive.

The aim of this study was to assess the association between impaired CR and adverse events in patients with diabetes referred for ETT.
Study Highlights

* In this prospective study, a cohort of 9569 patients was referred for ETT between July 2001 and June 2004 in Kaiser Permanente of Colorado. Of these patients, 1341 (14.0%) had diabetes and comprised the analytical cohort.
* Impaired CR was defined as achievement of less than 80% of a patient’s heart rate reserve at peak exercise or less than 62% for patients taking beta-blockers within 72 hours of ETT.
* A multivariable Cox proportional hazards regression was used to assess the independent association between impaired CR and adverse outcomes adjusting for demographics, comorbidities, and treadmill variables including the Duke Treadmill score.
* The primary outcome was the combined endpoint of all-cause mortality, hospitalization for acute myocardial infarction, or receipt of coronary revascularization procedures (coronary artery bypass graft surgery or percutaneous coronary intervention).
* Results demonstrated that of 1341 patients with diabetes, 35.7% (n = 479) demonstrated impaired CR during ETT.
* Patients with impaired CR were more likely to have a comorbid condition (eg, hypertension, coronary artery disease, peripheral vascular disease, and congestive heart failure) and abnormal heart rate recovery during ETT.
* Patients with impaired CR were at increased risk for all-cause mortality (4.2% vs 1.9%; P = .02), myocardial infarction (3.3% vs 1.7%; P = .06), and coronary revascularization procedures (23.8% vs 11.7%; P < .01).
* In multivariable analyses, impaired CR remained significantly associated with adverse outcomes (hazard ratio, 1.53; 95% confidence interval, 1.10 - 2.14).

Pearls for Practice

* As a result of autonomic dysfunction or alterations in sympathetic and parasympathetic tone, impaired CR is defined as the inability of the heart rate to increase normally with exercise.
* In a cohort of patients with diabetes, impaired CR is common during ETT and is associated with adverse outcomes including all-cause mortality, myocardial infarction, and coronary revascularization procedures.

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