Does unstable angina always change a person's electrocardiogram (EKG)?

Does Unstable Angina Always Change a Person's EKG?

No, unstable angina does not always cause changes on an electrocardiogram (EKG), as approximately 5% of patients with unstable angina may have a completely normal EKG even during symptoms. 1

ECG Findings in Unstable Angina

Common ECG Changes

• ST-segment depression (≥0.5 mm) in two or more contiguous leads is highly suggestive of unstable angina in the appropriate clinical context 1
• T-wave inversion (≥1 mm) in leads with predominant R waves is also indicative of unstable angina, though less specific than ST-segment depression 1
• Deep symmetrical T-wave inversion in anterior chest leads often indicates significant proximal left anterior descending coronary artery stenosis 1
• Transient episodes of bundle branch block may occasionally occur during ischemic attacks 1

Normal or Non-diagnostic ECG

• Several studies have shown that around 5% of patients with normal ECGs who were discharged from emergency departments were ultimately found to have either acute myocardial infarction or unstable angina 1
• Non-specific ST-segment and T-wave changes (<1 mm) may be present but are less reliable indicators 1
• A completely normal ECG recorded during an episode of significant chest pain should prompt consideration of other possible causes for the patient's complaints, but does not exclude unstable angina 1

Risk Stratification Based on ECG Findings

High Risk Features

• Angina at rest with transient ST-segment changes greater than 0.5 mm 1
• Bundle-branch block, new or presumed new 1
• Sustained ventricular tachycardia 1

Intermediate Risk Features

• T-wave changes 1
• Pathological Q waves or resting ST-depression less than 1 mm in multiple lead groups 1

Low Risk Features

• Normal or unchanged ECG during episodes of chest pain 1

Prognostic Significance of ECG Changes

• The 1-year incidence of death or new MI is 16.3% with ≥0.5 mm ST-segment deviation compared to 6.8% for isolated T-wave changes and 8.2% for no ECG changes 2
• ST-segment depression and T-wave inversion remain important predictors of outcome even in patients undergoing very early revascularization 3
• Continuous ST-segment monitoring can detect transient ischemic episodes that might be missed on standard 12-lead ECGs, improving risk stratification 4

Clinical Implications and Recommendations

• When unstable angina is suspected but the initial ECG is not diagnostic, serial ECGs should be performed at 15-30 minute intervals to detect potential development of ST-segment changes 1
• Ideally, an ECG should be obtained when the patient is symptomatic and compared with a tracing obtained when symptoms have resolved 1
• Comparison with previous ECGs, if available, is extremely valuable, particularly in patients with co-existing cardiac pathology 1
• Continuous ST-segment monitoring for 48 hours can identify patients at high risk, as 72% of patients with transient ischemia detected only by monitoring suffered adverse events 4

Pitfalls and Caveats

• Alternative causes of ST-segment and T-wave changes must be considered, including left ventricular hypertrophy, pericarditis, and other non-ischemic cardiac disorders 5
• Certain patient populations, such as the elderly, diabetics, and women, are more likely to present with atypical symptoms and non-diagnostic ECGs 6
• The distinction between unstable angina and NSTEMI is ultimately based on the detection of markers of myocardial necrosis in the blood, not solely on ECG findings 6
• A normal ECG during chest pain does not rule out unstable angina and should not provide false reassurance if clinical suspicion remains high 1