Stress Recovery Index (SRI) for Identifying Multivessel Coronary Artery Disease During Exercise Testing Following an Acute Myocardial Infarction

 

Protocol: described on page 1241 (Bigi et al, 1994):

(1) All cardioactive drugs were stopped for at least 48 hours.

(2) Patients were tested on an upright cycle ergometer.

(3) Warm-up was for 2 minutes at 15 W and 60 rpm.

(4) Exercise consisted of 25 W incremental loading every 180 seconds.

(5) The test was symptom-limited.

(6) Recovery was done in a sitting position.

 

An ischemic response was defined as:

(1) horizontal or downsloping ST segment depression >= 1 mm

(2) measured 60 seconds after the J point

(3) not measured in aVR or V1

(4) without pathologic Q waves

 

Criteria for discontinuation:

(1) onset of anginal pain

(2) repetitive arrhythmias

(3) significant conduction abnormalities

(4) ST depression > 3.0 mm

(5) limiting symptoms

(6) abnormal blood pressure (systolic > 230 mm Hg, drop of > 10 mm Hg, or failure to rise during increasing exercise)

 

Analysis was done on the ECG lead with the greatest ST depression, which usually was V4, V6 or aVF.

 

Parameters:

(1) baseline heart rate

(2) heart rate when exercise stopped

(3) time course of heart rate in beats per minute vs ST segment depression in mm during exercise

(4) time course of heart rate in beats per minute vs ST segment depression in mm during recovery, ending with return to the baseline heart rate

 

The areas under the 2 time course curves was then measured. This can be done by:

(1) planimetry

(2) summing geometric shapes (trapezoids, rectangles and triangles)

(3) weighing the curves (requires uniform paper, careful cutting and an accurate scale or the errors becomes significant)

(4) determining the equation that defines the curve then integrating

 

stress recovery index in (mm * beats per minute) =

= absolute value(area under time course curve during exercise) - absolute value(area under time course curve during recovery)

 

Interpretation:

• The stress recovery may take on a variety of positive or negative values depending on the changes during exercise and the speed of recovery.

• An SRI > -5 (mm * beats per minute) indicates single vessel coronary artery disease.

• An SRI <= -5 (mm * beats per minute) indicates multivessel coronary artery disease.

• The SRI was also predictive of mortality and nonfatal myocardial infarction in the 5 years following exercise testing (Bigi et al, 2005).

 

Performance:

• The sensitivity was 65% with specificity of 81%.

• The positive predictive value was 81% and negative predictive value was 64%.