What is the minimum ST segment depression in mm required for a positive treadmill stress test result?

ST Segment Depression Criteria for a Positive Treadmill Stress Test

The standard criteria for a positive treadmill stress test is horizontal or downsloping ST depression ≥1 mm (0.1 mV) at 60 to 80 ms after the J point. 1

Types of ST Depression and Their Diagnostic Value

• Horizontal or downsloping ST depression ≥1 mm (0.1 mV) is considered a positive standard ECG response indicating myocardial ischemia 1
• Upsloping ST depression ≥1 mm is considered an "equivocal" test response (a change that does not usefully separate normal from abnormal) 1
• ST depression <1 mm additional from baseline is defined as negative 1
• The ST level is measured relative to the end of the PR segment (the P–Q junction) because the T(U)–P segment during exercise is difficult to measure when heart rates are fast 1

Measurement Technique

• Three or more consecutive beats in the same lead with a stable baseline should be identified 1
• The average magnitude and tangent direction of displacement at 60 to 80 ms after the J point should be determined 1
• At ventricular rates >130 beats/min, 60 ms after the J junction is optimal to determine the extent of ST segment displacement in patients with an upsloping ST segment 1
• When modest resting ST depression is present on the upright control ECG before exercise, only additional ST depression during exercise is measured for analysis 1
• When the J point is elevated at rest (early repolarization), only ST-segment changes below the P-Q baseline should be used for analysis 1

Special Considerations

• Markedly depressed upsloping ST-depression responses to exercise (2.0 mm at 80 ms after the J point) could identify underlying CAD in highly symptomatic patients with angina 1
• More stringent criteria (≥1.5 mm ST depression) may be needed for patients on digitalis to maintain specificity 2
• The anatomic and functional severity of CAD can be related to the time of appearance of ischemic ST-segment depression - the lower the workload at which it occurs, the worse the prognosis 1
• The duration of ST depression in the recovery phase is also related to the severity of CAD 1
• The presence of both ST elevation and depression in the same test may indicate multivessel CAD 1

Limitations of Standard ST Depression Criteria

• Upsloping ST depression is generally considered an "equivocal" test response and is a major reason for the reduced sensitivity of the exercise ECG 1
• If upsloping ST depression were considered a positive response, it would result in unacceptably low specificity of the test 1
• Studies have shown that slow upsloping ST depression does not signify more severe ischemia or more extensive CAD compared to rapid upsloping ST depression 3, 4
• Adding upsloping ST-segment depression to the criteria for a positive exercise test increases sensitivity but decreases specificity and positive predictive value 4

Heart Rate Adjustment of ST-Segment Depression

• Heart rate adjustment of ST-segment depression can improve the sensitivity of the exercise test with preservation of test specificity 1
• The ST/HR slope >2.4 μV/bpm is considered abnormal, and values >6 μV/bpm are suggestive of anatomically extensive disease 1
• This approach requires an exercise protocol with gradual increments in heart rate 1

In conclusion, while various criteria have been proposed for interpreting ST depression during stress testing, the standard and most widely accepted criterion remains horizontal or downsloping ST depression ≥1 mm (0.1 mV) at 60 to 80 ms after the J point 1.