The Prognostic Importance of Abnormal Heart Rate Recovery and Chronotropic Response Among Exercise Treadmill Test Patients

Thomas M. Maddox, MD, MSc, FACC; Colleen Ross, MS; P. Michael Ho, MD, PhD, FACC; Frederick A. Masoudi, MD, MSPH, FACC; David Magid, MD, MPH; Stacie L. Daugherty, MD, MSPH; Pam Peterson, MD, MSPH, FACC; John S. Rumsfeld, MD, PhD, FACC

Disclosures

Am Heart J. 2008;156(4):736-744. 

In This Article

Abstract and Introduction

Abstract

Background: Heart rate recovery (HRR) and chronotropic response to exercise (CR) each have prognostic value among patients undergoing exercise treadmill testing (ETT). However, little is known about their prognostic use in combination and in addition to the Duke Treadmill Score (DTS).
Methods: We studied 9,519 outpatients undergoing ETT between 2001 and 2004. Patients were categorized by HRR and CR. The primary outcome was all-cause mortality or nonfatal myocardial infarction (MI). Cox proportional hazards modeling was used to control for demographics, clinical history, and DTS.
Results: After multivariable adjustment for DTS and other demographic and clinical variables, patients with abnormal HRR and CR had higher rates of all-cause mortality or nonfatal MI, as compared to patients with normal HRR and CR (hazard ratio [HR] = 1.90, 95% CI 1.35-2.69). Addition of the HRR and CR to the DTS improved outcome prediction (c-statistic improved from 0.61 to 0.68). Low-risk DTS patients with abnormal HRR and CR had significantly higher rates of all-cause mortality or nonfatal MI (HR 2.59, 95% CI 1.55-4.32), compared to low-risk DTS patients with normal HRR and CR.
Conclusions: Abnormal HRR and CR identified ETT patients with higher rates of all-cause mortality or nonfatal MI and provided additional risk stratification among low-risk DTS patients. These results support the routine incorporation of HRR and CR in ETT reporting and suggest the need to evaluate whether further testing and/or more intensive treatment of these higher risk patients can improve outcomes.

Introduction

Exercise treadmill testing (ETT) provides a variety of prognostic information, including symptom assessment, functional capacity, hemodynamic responses to exercise, and electrocardiographic (ECG) changes in exercise and recovery among patients with suspected or known coronary artery disease (CAD).[1,2,3,4,5,6,7,8,9,10,11] To assist with clinical interpretation of this information, the Duke Treadmill Score (DTS) was developed.[12,13,14,15,16] The DTS uses exercise capacity, symptoms, and ST-segment changes to stratify patients into low, intermediate, and high-risk scores, and is prognostic of all-cause and cardiac mortality.[12]

However, the DTS fails to incorporate other important data from the ETT. Abnormalities in heart rate recovery (HRR) and chronotropic response (CR) to exercise are each associated with all-cause mortality and cardiac events.[4,6,8,10,11,17,18,19] How best to integrate this data into a clinically interpretable form with the DTS is currently unknown. Accordingly, we hypothesized that the combination of abnormal HRR and CR was associated with all-cause mortality or nonfatal myocardial infarction (MI), even after adjustment for demographics, clinical history, and DTS and can add to the prognostic information provided by the DTS.

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