Exercise ECG

• ExECG has a positive likelihood ratio of 2.18 and a negative likelihood ratio of 0.32 for CAD¹
• Involves graded exercise until physical fatigue, limiting chest pain (or discomfort), marked ischemia, or a drop in blood pressure occurs.²
• Goal is at least 4-6 minutes of exercise to allow for maximal metabolic demand
• METS needs to be ≥5 for stress study to be interpretable (ask Talal for citation)
  • Adequate workload in a patient undergoing stress ECG testing is defined as ≥5 METS
• Ideally, tests should be symptom limited (i.e. not “done” when patient reaches 85% of max-predicted HR)
• Candidates for exercise ECG are those:²
  • without disabling comorbidity (e.g., frailty, marked obesity (BMI >40 kg/m2), PAD, COPD, or orthopedic limitations) and capable of performing ADLs or able to achieve ≥5 METs and
  • without resting ST-T abnormalities (e.g., >0.5-mm ST depression, LVH, paced rhythm, LBBB, WPW pattern, or digoxin use).
    • Confounders such as resting ST-segment depression, digoxin usage, and LVH with repolarization changes decrease specificity. Despite these confounders, ExECG is still considered diagnostic in most patients able to reach 85% of their maximum age-predicted heart rate.¹
• Indications
  • ischemic evaluation
  • chronotropic incompetence
  • exercise induced arrhythmias
  • valve disease, e.g. severe aortic stenosis
• Options:
  • Treadmill
  • Recumbent bicycle
  • Protocols (Bruce, modified Bruce, Naughton)
• Contraindications
  • Abnormal ST changes on resting ECG, digoxin, LBBB, WPW pattern, ventricular paced rhythm (unless test is performed to establish exercise capacity and not for diagnosis of ischemia)
    • LVH, LBBB, digoxin effect, V-paced rhythm, pre-excitation/WPW pattern, resting ST abnormalities, ?RBBB (V1-V3, the rest of the leads are interpretable though) as these would be uninterpretable based on ECG assessment alone
  • Unable to achieve ≥5 METs or unsafe to exercise
  • High-risk unstable angina or AMI (<2 d) i.e., active ACS
  • Uncontrolled HF
  • Significant cardiac arrhythmias (e.g., VT, complete atrioventricular block) or high risk for arrhythmias caused by QT prolongation
  • Severe symptomatic aortic stenosis
  • Severe systemic arterial hypertension (e.g., ≥200/110 mm Hg)
  • Acute illness (e.g., acute PE, acute myocarditis/pericarditis, acute aortic dissection)
• Widely available and inexpensive
• Interpretable ECG
• Requires ability to exercise to an adequate level
• Who should you test?
  • Intermediate-risk ASx adults (including considering starting a vigorous exercise program), particularly when attention is paid to exercise capacity
• Limited diagnostic accuracy
  • sensitivity ~60% & specificity ~70%
• Avoid if pre-existing ECG abnormalities
• What are you looking for?
  • See slide
• Prognostic importance of functional capacity
  • Once > 10 METS your prognosis, regardless of whether you have CAD or not, is quite good)
  • 
    • Figure source: 📄 Myers J, Prakash M, Froelicher V, Do D, Partington S, Atwood JE. Exercise Capacity and Mortality among Men Referred for Exercise Testing. New England Journal of Medicine. 2002;346(11):793-801. doi:10.1056/nejmoa011858
• Value add of Coronary Artery Calcium (CAC) Score
  • See 📄 Chang SM, Nabi F, Xu J, et al. Value of CACS Compared With ETT and Myocardial Perfusion Imaging for Predicting Long-Term Cardiac Outcome in Asymptomatic and Symptomatic Patients at Low Risk for Coronary Disease. JACC: Cardiovascular Imaging. 2015;8(2):134-144. doi:10.1016/j.jcmg.2014.11.008
  • 

Baseline ECG abnormalities

• Resting STD ≥1 mm
• digoxin usage
• LBBB
  • require vasodilator MPI imaging due to a high false-positive rate
• WPW pattern
• Ventricular paced rhythm (unless test is performed to establish exercise capacity and not for diagnosis of ischemia)

Stress ECG Interpretation

• Abnormal responses to exercise on stress include:
  • Heart rate fails to rise above 120 bpm or unable to attain 85% of MPHR
  • Drop in systolic BP
  • Physically unable to complete test
  • Marked hypertension, >220/110
  • Chest Pain and/or unusual shortness of breath

ST segments

• Review of ST segment - “positive” response is indicated by:
  • ST segment depression (horizontal or downsloping) of > 1mm
    • 80 msec from the J-point
  • ST segment elevation in leads lacking Q-waves
  • 
• ST-segment elevation in lead aVR¹
  • Lead aVR is often neglected in ExECG interpretation but has unique vector positioning. This allows it to function as a “pseudo-intracavitary” lead that may identify anterior wall transmural ischemia.
  • Uthamalingam et al. found a ≥1 mm aVR elevation during ExECG to be the strongest predictor of an obstructive LM or ostial LAD artery stenosis with a diagnostic accuracy of 80% and a 2.6-fold increase in post-test probability.
• Presence of arrhythmias

Duke Treadmill Score

Chronotropic Response

• If HR <80-ish%, cannot say completely negative test
  • Heller et al. found that reaching only 70% compared with ≥85% of maximum age-predicted heart rate leads to a reduction in the incidence of stress defects from 100% to 47% and a reduction in angina from 84% to 26%.
• Exercise ECG is considered diagnostic if able to achieve ≥85% MPHR
• If unable to achieve 80% of MPHR, can call is “chronotropic incompetence”

Prognostic Features

Failure to achieve target HR

Exercise capacity

• Patients achieving ≥10 METs on ExECG have a very low prevalence of inducible ischemia and an excellent prognosis¹
• High exercise workload is also a marker of a decreased risk of cardiac events, including cardiac death, nonfatal MI, and coronary revascularization. These associations remain even in the setting of ischemic ST-segment depression.¹
• Bourque et al. found that patients attaining <7 metabolic equivalents (METs) had an 18-fold higher prevalence of substantial (≥10%) LV ischemia compared with those reaching ≥10 METs. The latter group with good exercise tolerance had a very low (0.4%) prevalence of ≥10% LV ischemia.¹
  • 

Post-exercise

Abnormal heart rate recovery

• <12 bpm HR drop 1 min post-exercise (1 min into recovery)
  • Cole et al. found a relative risk of death of 2.0 (95% confidence interval: 1.5 to 2.7; p < 0.001) for those with a <12-beats/min heart rate drop 1 min post-exercise after risk factor adjustment in 2,428 patients¹
• <22 bpm HR drop 1 min post-exercise
  • A retrospective analysis of 2,193 men found a heart rate recovery <22 beats/min at 2 min to be predictive of mortality and the presence of CAD¹
• 📝 O’Keefe mentioned that this is a reflection of vagal tone (i.e., healthy hearts will have healthy vagal tone), and he will often use ≥ 20 bpm reduction at 2 minutes b/c practically 1 minute is not always captured well.

Abnormal blood pressure recovery

• SBP ≥15% by 3 min post-exercise
  • An abnormal SBP recovery ratio of >0.9 (SBP at 3 min/SBP at peak exercise) has been found to have comparable diagnostic accuracy to ST-segment depression and incremental value for the identification of CAD¹
    • correlates with the extent and severity of thallium-201 perfusion defects

• 10-mm Hg SBP drop during exercise and a delayed decline in SBP after exercise have been associated with high-risk multivessel or left main disease in men with less specificity in women

Indications for Early Termination of Exercise

• Moderate to severe angina pectoris
• Excessive STD (horizontal or downsloping) >2 mm from baseline in a patient with suspected ischemia
• STE (>1.0 mm) in leads without diagnostic Q-waves (except for leads V1 or aVR).
• Sustained SVT or VT
• Development of symptomatic second- or third-degree AV block without functioning pacemaker
• Development of LBBB or IVCD that cannot be distinguished from VT
• Signs of poor perfusion (cyanosis and pallor)
• Hypertensive response (SBP >230 mmHg and/or DBP >115 mmHg)
• Severe hypotension (SBP <80 mmHg)
• Drop in SBP of >10 mmHg from baseline, despite an increase in workload, when accompanied by other evidence of ischemia
• Inability to monitor the ECG or BP
• In patients with ICDs, when the heart rate attained is within 20 bpm of the lowest heart rate at which therapy (antitachycardia pacing or shock) is programmed to be delivered
• Patient’s request to stop

Footnotes

1. Bourque JM, Beller GA. Value of Exercise ECG for Risk Stratification in Suspected or Known CAD in the Era of Advanced Imaging Technologies. JACC Cardiovasc Imaging. 2015 Nov;8(11):1309-21. doi: 10.1016/j.jcmg.2015.09.006. PMID: 26563861; PMCID: PMC4646721. ↩ ↩² ↩³ ↩⁴ ↩⁵ ↩⁶ ↩⁷ ↩⁸ ↩⁹

2. Gulati M, Levy PD, Mukherjee D, et al. 2021 AHA/ACC/ASE/CHEST/SAEM/SCCT/SCMR Guideline for the Evaluation and Diagnosis of Chest Pain. Journal of the American College of Cardiology. 2021;78(22):e187-e285. doi:10.1016/j.jacc.2021.07.053 ↩ ↩²