ECG exercise tolerance testing (ETT)

Introduction

Also referred to as a stress test, a diagnostic test in which the patient exercises on a treadmill, bicycle, or other equipment while heart activity is monitored by an ECG.

Indications

• initial diagnostic study for coronary artery disease (CAD) in most patients*
  • evaluation of chest pain (typical or atypical for angina)
  • latent CAD
• evaluation of severity & prognosis of CAD
• evaluation of functional capacity
• evaluation of therapy (medical &/or surgical)
• evaluation of arrhythmia
  • arrhythmias that occur spontaneously with exercise
    • most arrhythmias are not exercise related
  • peak heart rate in a patient with an implantable defibrillator
  • ventricular response in patients with atrial fibrillation
  • response of rate-responsive pacemaker during exercise
• post MI predischarge evaluation
• evaluation of hypoxemia or oxygen desaturation

* high sensitivity for left main, 3-vessel & severe 2-vessel coronary artery disease

Contraindications

• absolute
  • acute myocardial infarction (<10 days)
  • uncontrolled, unstable angina
  • decompensated congestive heart failure
  • active myocarditis or pericarditis
  • uncontrolled major arrhythmia
    • ventricular
    • supraventricular
    • heart block
  • excessive hypertension (systolic BP > 200 mm Hg)
  • marked postural hypotension (systolic BP drop > 20 mm Hg)
  • critical aortic stenosis
    • severe aortic stenosis with worsening symptoms
  • other major acute illness
• relative: (renders test uninterpretable)
  • left ventricular hypertrophy (LVH)
  • atrial fibrillation
  • digoxin
  • left bundle branch block (LBBB)
  • mitral valve prolapse
  • T-wave abnormalities
  • ST segment abnormalities (> 0.5 mm ST segment depression)
  • paced rhythm
  • WPW syndrome
  • prior revascularization
• routine screening of asymptomatic patients

Advantages

• provides data on
  • exercise capacity
  • blood pressure & heart rate response to exercise
  • possibly, provoked symptoms

Disadvantages

• not useful when baseline ECG is abnormal#
• accuracy depends on pretest probability of disease
• abnormalities predict increased risk, but with uncertain implications regarding treatment
• ischemia on exercise stress testing does not predict cardiovascular events or change in LV ejection fraction in patients with stable multivessel coronary artery disease

# see Contraindications

Procedure

• Bruce protocol
• Naughton protocol
• Blake protocol
• Ellestad protocol

Discontinue beta-blocker 24-48 hours prior to testing

The extremity electrodes are moved to the torso to reduce motion artifact. The arm electrodes are placed in the lateral aspect of the infraclavicular fossa & the leg electrodes are placed above the iliac crest & the rib cage. This results in a right axis shift & increased voltage in inferior leads. It may result in a loss of inferior Q waves &/or development of a new Q wave in aVL.

Reasons for terminating a stress test

• fatigue or dyspnea on exertion
• maximum heart rate
• angina (3 out of 4)
• progressive ST segment depression
• arrhythmia
  • ventricular tachycardia (a run of 3 or more PVCs)
  • rapid supraventricular arrhythmia
  • heart block
• blood pressure (BP) abnormalities
  • progressive drop in BP with increasing workload (> 20 mm Hg)
  • anxious normal individuals may drop BP during stage I
  • excessive elevation of systolic BP (> 250 mm Hg)
• signs of hypoperfusion
  • lightheadedness
  • pale color
  • clammy skin
• intermittent claudication
• musculoskeletal limitations or balance difficulties
• other reasons

Criteria for positive ECG response

• normal resting ST segment
  • > 1 mm ST segment depression in 2 contiguous ECG leads
  • 1 mm J point depression with horizontal or downsloping ST segment
  • 1.5 mm ST depression at 80 msec after the J point with upsloping ST segment
• abnormal resting ST segment
  • 2 mm of additional ST segment depression
• patient on digitalis
  • same criteria as normal resting ST segment if patient achieves > 90% maximum predicted heart rate

* 1 mm horizontal ST segment depression that resolves in the 1st minute of recovery does not meet criteria for further testing, but does suggest a component ischemic heart disease

• cardiac rehabilitation is recommended vs myocardial perfusion testing (pharmacologic testing) or cardiac catheterization

Blood pressure:

• normal response of systolic blood pressure to increasing workloads is 160-200 mm Hg
  • also see hypertensive response to exercise
• in normal subjects, diastolic blood pressure does not change significantly
• failure to increase systolic blood pressure to > 120 mm Hg or sustained decreased in systolic blood pressure > 10 mm Hg below standing resting values is abnormal
  • myocardial ischemia
  • cardiomyopathy
  • cardiac arrhythmias
  • vasovagal reactions
  • left ventricular outflow obstruction
  • ingestion of antihypertensive drugs
  • hypovolemia
  • prolonged vigorous exercise

Other prognostic/diagnostic factors:

• achievement of a high workload (good prognosis)
• typical angina during exercise
  • adds diagnostic & prognostic information
  • occurring at < 6 METS (before the end of stage 2 of the Bruce protocol) is an indication for coronary angiography
• persistence of ST segment depression into recovery
• increased heart rate of > 12/min during 1st minute of exercise is associated with increased risk of myocardial infarction
• self-reported dyspnea is an independent risk factor for myocardial infarction
• high-grade premature ventricular contractions during the recovery period following exercise may be associated with increased cardiovascular risk
• higher incidence of false-positive ST segment depression in women*
• sensitivity is also lower in women*

* recommendations are generally the same for men & women

Management

• a positive test warrants referral for myocardial perfusion test or cardiac catheterization
• stress echocardiography if baseline ST segment abnormalities (> 0.5 mm ST segment depression) confound interpretation
• if the exercise stress test is inadequate, a pharmacologic stress test should be performed
• symptomatic patients with an abnormal test that does not meet criteria for a positive test may benefit from cardiac rehabilitation
• Duke treadmill score may provide useful risk information

Notes

• rapid resolution of ECG changes during exercise portends negative followup testing & good prognoses
• angina pectoris despite negative ECG findings portends positive followup testing & poorer prognosis
• chest tightness & breathlessness in a man with history of myocardial infarction in the absence of ECG changes constitutes low risk
• younger age, female sex, & achieving a higher level of exercise portend negative followup testing

More general terms

• exercise stress testing

More specific terms

• Bruce protocol
• Ellestad protocol
• Naughton protocol
• post-MI exercise testing; rehabilitation treadmill testing; predischarge exercise testing

Additional terms

• Duke treadmill score
• electrocardiogram (ECG, EKG)
• hypertensive response to exercise (HRE)