Conducting Stress Test Interpretation

Conducting Stress Test Interpretation

Interprets exercise and pharmacologic stress tests with Duke treadmill score and nuclear findings.

Why This Skill Exists

Cardiac stress testing is the most widely used non-invasive method for evaluating suspected coronary artery disease, with over 10 million tests performed annually in the US. The choice of stress modality (exercise vs. pharmacologic) and imaging (ECG alone, echo, nuclear, CMR) must be matched to the clinical question and pretest probability. Misinterpretation — a false-negative treadmill ECG in a patient with LBBB, or failure to recognize balanced ischemia on perfusion imaging — can result in missed high-risk disease.

The Duke Treadmill Score (DTS) provides validated risk stratification for exercise ECG, and ACC Appropriate Use Criteria define when imaging should be added. This skill enforces systematic interpretation aligned with these evidence-based frameworks.

Checkpoint A: Pre-Draft Intake (Mandatory)

1. What was the clinical indication — chest pain evaluation, preoperative risk, post-revascularization assessment, arrhythmia evaluation? (default: "Chest pain / CAD evaluation")
2. What stress modality was used — treadmill exercise, pharmacologic (regadenoson, adenosine, dipyridamole, dobutamine)? (default: "Treadmill exercise")
3. What imaging was used — ECG only, echocardiography, SPECT MPI, PET MPI, or CMR? (default: "ECG only")
4. Can the patient exercise adequately (≥ 85% MPHR)? (default: "Exercise capacity unknown")
5. Is the baseline ECG interpretable for ischemia (no LBBB, no LVH with repolarization abnormality, no digoxin, no paced rhythm, no WPW)? (default: "Baseline ECG interpretability not assessed")
6. What is the pretest probability of CAD? (default: "Intermediate — to be calculated")
7. Is there a prior stress test for comparison? (default: "No prior study available")
8. What medications is the patient taking (beta-blockers, CCBs, nitrates, caffeine)? (default: "Not provided")

Documents to Request

• Complete stress test report with images/tracings
• Pre- and post-stress ECGs (all stages)
• Perfusion images (stress and rest) if nuclear study
• Wall motion images at rest and stress if echo or CMR
• Bruce protocol or specific treadmill protocol used
• BP and HR data at each stage
• Prior stress test for comparison
• Recent ECG for baseline interpretation
• Current medication list (beta-blocker held or continued)

Step 1: Exercise Parameters and Adequacy Assessment

Exercise Adequacy Criteria:

• Target heart rate: ≥ 85% of age-predicted maximum (220 − age)
• Submaximal test (< 85% MPHR) has significantly lower sensitivity — document and note limitation
• If pharmacologic stress: confirm appropriate agent delivery and hemodynamic response

Exercise Capacity Assessment:

Bruce Protocol Stages:

Reasons for Test Termination (document which applies):

• Target HR achieved
• Maximal exertion (patient request, fatigue)
• Significant ST depression (≥ 2 mm horizontal/downsloping)
• Sustained VT or symptomatic arrhythmia
• Drop in SBP > 10 mmHg from baseline with ischemic signs
• Severe hypertensive response (SBP > 250, DBP > 115)
• Moderate-to-severe angina

Step 2: ECG Interpretation During Stress

Positive ECG Criteria for Ischemia:

• ≥ 1 mm horizontal or downsloping ST depression at 60–80 ms after J point
• ≥ 1 mm ST elevation in leads without pathologic Q waves (transmural ischemia)
• ST depression in ≥ 5 leads and/or persisting > 5 minutes into recovery suggests severe/multivessel disease

False-Positive Causes (reduced specificity):

• Baseline ST abnormalities (LVH, digoxin effect, LBBB)
• Mitral valve prolapse
• Female sex (lower specificity)
• Hypokalemia
• Pre-excitation (WPW)

False-Negative Causes (reduced sensitivity):

• Submaximal heart rate (< 85% MPHR)
• Anti-ischemic medications (beta-blockers, nitrates, CCBs)
• Single-vessel disease (especially LCx)
• Delayed ischemia timing

Step 3: Duke Treadmill Score Calculation

Formula: DTS = Exercise time (minutes, Bruce protocol) − (5 × maximum ST deviation in mm) − (4 × angina index)

Angina Index:

• 0 = no angina
• 1 = non-limiting angina
• 2 = exercise-limiting angina

Risk Stratification:

Step 4: Nuclear Perfusion / Stress Echo / PET Interpretation

SPECT MPI Interpretation Framework:

1. Perfusion defect location (mapped to coronary territory — LAD, LCx, RCA)
2. Defect severity: mild, moderate, severe
3. Defect reversibility: fixed (scar), reversible (ischemia), partially reversible (peri-infarct ischemia)
4. Summed stress score (SSS), summed rest score (SRS), summed difference score (SDS)
   • SSS < 4: normal
   • SSS 4–8: mildly abnormal
   • SSS 9–13: moderately abnormal
   • SSS ≥ 14: severely abnormal
5. Transient ischemic dilation (TID) ratio > 1.22 → balanced ischemia or multivessel disease
6. Post-stress LVEF and wall motion

Stress Echocardiography Interpretation:

• Compare resting and post-stress wall motion in 17-segment model
• New or worsening wall motion abnormality = ischemia (map to territory)
• Fixed abnormality = scar
• Hyperdynamic response with no new WMA = normal

High-Risk Imaging Findings (regardless of modality):

• Large perfusion defect (> 10% myocardium)
• Multiple-territory ischemia
• Transient ischemic dilation
• Post-stress LVEF drop > 5%
• Stress-induced RV visualization on SPECT (RV strain marker)

Step 5: Integrated Report and Recommendations

Structured Report Must Include:

1. Indication and clinical context
2. Protocol used and stress modality
3. Exercise duration, METs achieved, peak HR and % MPHR
4. Hemodynamic response (BP, HR, rate-pressure product)
5. ECG findings at peak exercise and recovery
6. Imaging findings (perfusion, wall motion, LVEF)
7. Duke Treadmill Score (if exercise ECG)
8. Overall interpretation: normal, equivocal, abnormal (with severity)
9. Risk category and recommendation (medical management, additional imaging, catheterization)
10. Comparison with prior study

Checkpoint B: Post-Draft Alignment (Mandatory)

1. Was exercise adequacy (% MPHR and METs) documented?
2. Were ECG changes described with timing, leads, and morphology?
3. Was the Duke Treadmill Score calculated for exercise ECG tests?
4. Were imaging findings mapped to specific coronary territories?
5. Does the final recommendation align with the risk stratification?

Quality Audit

• Clinical indication documented
• Protocol and stress modality specified
• Exercise duration and METs achieved reported
• Peak HR and percentage of MPHR calculated
• BP response documented at rest, peak, and recovery
• Reason for test termination stated
• ECG changes described with quantitative ST deviation
• Duke Treadmill Score calculated (exercise ECG tests)
• Perfusion defects described by location, severity, and reversibility (nuclear)
• Wall motion analysis compared rest vs. stress (echo)
• High-risk features explicitly assessed (TID, multi-territory ischemia, EF drop)
• Medications held or continued noted (beta-blockers, caffeine)
• Risk category assigned with next-step recommendation
• Prior study comparison documented or absence noted
• Appropriate use criteria met for the chosen modality

Guidelines

1. Exercise ECG alone (no imaging) is appropriate only when the baseline ECG is interpretable for ischemia and the patient can exercise adequately. If LBBB, LVH with repolarization changes, paced rhythm, WPW, or digoxin effect is present, imaging must be added.
2. Beta-blockers should be held for 24–48 hours before a diagnostic stress test for ischemia evaluation, unless clinically unsafe to discontinue.
3. Caffeine must be held for 12–24 hours before vasodilator stress (regadenoson, adenosine, dipyridamole) — it competitively antagonizes the pharmacologic effect.
4. A normal stress test at peak exercise (≥ 85% MPHR, ≥ 10 METs, no ECG changes) has > 99% negative predictive value for adverse cardiac events at 1 year.
5. The Duke Treadmill Score should be calculated for every exercise ECG test — it provides incremental prognostic information beyond ST changes alone.
6. Fixed defects on nuclear imaging should be correlated with clinical history and wall motion — some fixed defects represent hibernating myocardium amenable to revascularization (assess viability).
7. When stress test results are discordant with clinical suspicion, document the discrepancy and recommend additional testing (e.g., coronary CT angiography or catheterization).