Normal ST-Segment Levels During Recovery Phase of Treadmill Testing
In normal subjects, the J-point depression that occurs at peak exercise gradually returns to pre-exercise baseline values during recovery, with ST-segment levels at Recovery 1 (first minute) and Recovery 3 (third minute) progressively normalizing toward the isoelectric baseline. 1
Expected ST-Segment Behavior in Normal Recovery
Recovery Phase Dynamics in Normal Subjects
The J-point (junction between QRS end and ST-segment beginning) becomes depressed at maximum exercise and then gradually returns to pre-exercise values during the recovery period. 1
In normal individuals, ST-segment depression at 1 minute of recovery is typically LESS than it was at the same heart rate during the exercise phase, distinguishing normal from ischemic responses. 1
By Recovery 3 (third minute), the ST-segment should be approaching or have returned to baseline (pre-exercise) levels in normal subjects. 1
Quantitative Normal Findings
Upsloping ST depression at peak exercise may be seen in 10% to 20% of normal subjects, and this gradually resolves during recovery. 1
J-point depression is more common in older patients but should still normalize progressively during recovery. 1
Any ST-segment depression <1.0 mm (0.1 mV) measured 60-80 ms after the J-point is considered within normal limits. 2
Key Measurement Principles for Recovery Phase
Baseline Reference Point
The P-Q junction (end of PR segment) serves as the isoelectric baseline for measuring ST-segment levels during recovery, particularly when heart rates remain elevated above 130 bpm. 3
ST-segment deviation should be measured at the J-point and again 60-80 ms after the J-point to determine the magnitude and morphology of any displacement. 3
Special Considerations for Early Repolarization
In subjects with resting J-point elevation due to early repolarization, the ST level normalizes with exercise and recovery; this normalization is a normal finding and should not be misinterpreted as ST depression. 1
When baseline J-point elevation progressively becomes more depressed during exercise, ST-segment displacement is measured from the P-Q junction, not from the elevated resting J-point. 3
Distinguishing Normal from Abnormal Recovery Responses
Normal Recovery Pattern
In normal subjects, ST-segment depression (if present at peak exercise) decreases more rapidly during recovery than in patients with ischemia. 1
The ST/HR relationship during recovery shows that normal subjects have less ST depression at any given heart rate during recovery compared to the same heart rate during exercise. 1
Abnormal Recovery Pattern (Ischemia)
ST depression attributable to ischemia is generally GREATER at 1 minute of recovery than it was at the same heart rate during exercise, representing abnormal ST/HR hysteresis. 1
ST depression persisting beyond 8 minutes into recovery is associated with a 90% prevalence of two- to three-vessel or left main coronary artery disease. 4
Clinical Pitfalls to Avoid
Common Measurement Errors
Do not use the T-P segment as a reference during recovery if heart rate remains >130 bpm, as T-P wave fusion makes this unreliable. 3
Errors occur when the end of the PR segment is incorrectly placed on the descending limb of a shortened P wave, leading to inaccurate automated ST-segment measurements. 3
Ensure consistent electrode placement, as displacement of even 1 cm can produce significant waveform changes and false ST-segment abnormalities. 3
Interpretation Nuances
Recovery-only ST depression (appearing only during recovery, not during exercise) has limited diagnostic value compared to exercise-phase ST depression, with lower prevalence of significant coronary stenosis. 5
However, recovery-only ST depression should not be dismissed entirely, as some studies show 50-65% of these patients may still have significant coronary artery disease. 5, 6
The combination of exercise AND recovery ST depression identifies patients with more severe prognosis compared to either phase alone. 7