Is ST‑segment deviation >1 mm during the recovery phase of an exercise treadmill test abnormal, what is the normal value, what is the associated risk, and what is the recommended next step?

ST-Segment Depression >1 mm in Recovery Phase: Abnormal Finding Requiring Further Evaluation

Yes, ST-segment depression ≥1 mm during the recovery phase of a treadmill test is abnormal and carries significant prognostic implications similar to ST changes occurring during active exercise, warranting stress imaging as the next step.

Normal Values and Diagnostic Thresholds

The normal value for ST-segment depression is <1 mm from baseline 1. The American Heart Association defines abnormal ST-segment response as:

• Horizontal or downsloping ST depression ≥1 mm (0.1 mV) measured at 60-80 ms after the J point 1, 2
• ST depression ≥1 mm at <5 METs or persisting >5 minutes into recovery indicates high-risk findings 1
• ST depression <1 mm is considered negative 1

Risk Stratification of Recovery-Phase ST Depression

Prognostic Significance

Recovery-phase ST depression carries similar adverse prognostic significance to ST changes appearing during active exercise 3. Key risk indicators include:

• Independent predictor of coronary events: In asymptomatic individuals, recovery-limited ST depression showed an odds ratio of 2.38 for future cardiac events, comparable to exercise-phase changes (OR 2.59) 3
• Duration matters: The longer ST depression persists in recovery, the more severe the underlying coronary artery disease 1
• Ischemic pattern: After 1 minute of recovery, ST depression attributable to ischemia is generally greater than it was at the same heart rate during exercise, whereas in normal subjects it is less 1

Severity Assessment

The magnitude and characteristics of recovery ST depression correlate with disease severity 1:

• ≥2 mm ST depression suggests more extensive coronary disease 1
• Counterclockwise rate-recovery loops (where ST depression increases relative to heart rate during recovery) have 93% sensitivity for angiographically proven coronary disease 4
• Recovery-phase limited ST depression (without exercise-phase changes) shows lower prevalence of significant stenosis (50% vs 67%) and lower Gensini scores compared to exercise-phase depression 5

Recommended Next Steps

Immediate Action Algorithm

The American Heart Association recommends stress imaging as the definitive next step for abnormal or indeterminate exercise treadmill tests 1:

1. Stress echocardiography or myocardial perfusion imaging should be performed to:

   • Confirm presence of inducible ischemia
   • Localize affected coronary territories
   • Quantify extent and severity of ischemia
   • Guide decisions about coronary angiography 1

2. Consider the clinical context:

   • Assess ongoing symptom burden
   • Evaluate other high-risk markers from the treadmill test (exercise capacity <5 METs, abnormal heart rate recovery ≤12 bpm, hypotensive response) 1
   • Calculate Duke Treadmill Score (high-risk if ≤-11) 1

Integration with Other Test Parameters

The American Heart Association emphasizes that ETT interpretation should include multiple parameters beyond ST-segment response 1:

• Exercise capacity and functional capacity achieved
• Chronotropic response (heart rate recovery)
• Blood pressure response (decrease >10 mmHg indicates high risk) 1
• Presence and timing of anginal symptoms
• Ventricular arrhythmias during recovery 1

Important Clinical Caveats

Diagnostic Pitfalls to Avoid

• Recovery-only ST depression may have slightly lower diagnostic accuracy than exercise-phase changes, but still requires investigation 5
• Upsloping ST depression ≥1 mm is considered equivocal unless it reaches ≥2 mm at 80 ms after the J point in highly symptomatic patients 1
• False positives can occur with left ventricular hypertrophy, baseline ST abnormalities, and certain medications 6
• ST/HR hysteresis analysis (comparing ST depression at matched heart rates during exercise vs recovery) provides higher diagnostic accuracy than standard criteria alone 1

When to Expedite Evaluation

Proceed urgently to stress imaging or consider direct angiography if 1:

• ST depression ≥2 mm in multiple leads
• ST depression occurring at low workload (<5 METs)
• Prolonged recovery (>5 minutes)
• Accompanied by symptoms, hypotension, or ventricular arrhythmias