Should a 12-lead electrocardiogram (ECG) be performed on a patient to assess their cardiac rhythm?

When to Perform a 12-Lead ECG

A 12-lead ECG should be performed in the initial evaluation of patients with cardiac symptoms (chest pain, dyspnea, palpitations, syncope, lightheadedness), known or suspected cardiovascular disease, before starting certain medications, and in specific clinical scenarios outlined below. 1

Essential Indications for ECG

Symptomatic Patients (Class I - Strongly Recommended)

• Perform ECG immediately in patients presenting with chest pain, dyspnea, palpitations, syncope, or near-syncope 1, 2
• Obtain ECG in patients with unexplained fatigue, weakness, prostration, or new/worsening angina patterns 1
• Record ECG when patients develop lightheadedness or palpitations, particularly in those with known cardiac conditions 1

The ECG provides diagnostic information in approximately 5% of syncope presentations and identifies underlying structural heart disease that predicts adverse outcomes and mortality 1. While the diagnostic yield may seem modest, an abnormal ECG is strongly associated with increased all-cause mortality at 1 year in patients presenting with syncope 1.

Known Cardiovascular Disease

• Obtain baseline and periodic ECGs (every 1-2 years) in patients with hypertrophic cardiomyopathy for rhythm assessment and detection of conduction abnormalities 1
• Perform serial ECGs in patients with acute ischemia to monitor response to thrombolytic or anti-ischemic therapy 1
• Record ECG after coronary angioplasty or intracardiac procedures until stable and before discharge, even with uncomplicated procedures 1
• Obtain ECG in patients with structural heart disease, previous arrhythmias, or reduced ventricular function 1

Medication Monitoring (Class I)

Before and during therapy with drugs that produce cardiac effects:

• Antiarrhythmic drugs: Serial ECGs assess conversion to sinus rhythm, QRS duration, QT prolongation, and proarrhythmia 1
• Psychotropic agents: Phenothiazines, tricyclic/tetracyclic antidepressants, lithium 1
• Anti-infective agents: Erythromycin, pentamidine 1
• Cardiovascular medications: Diuretics, ACE inhibitors, calcium channel blockers, beta-blockers, digitalis, dopamine, dobutamine 1
• Lacosamide: Obtain baseline ECG in patients with cardiac history, syncope, structural heart disease, or those on PR-prolonging drugs (beta-blockers, calcium channel blockers, digoxin) 3
• ADHD medications (Adderall): Baseline ECG recommended for patients with cardiac risk factors; consider cardiology consultation 4, 5

The American Heart Association emphasizes that ECG recordings are appropriate after drug initiation, therapy changes, and addition of interacting medications 1.

Procedural Indications

• Cardioversion: ECG immediately before, immediately after, and before discharge for ventricular tachycardia, supraventricular tachycardia, atrial fibrillation, or atrial flutter 1
• Pacemaker management: ECG soon after insertion/revision, when malfunction suspected, after lead threshold maturation, and at periodic intervals throughout device lifetime 1
• Cardiac surgery: Serial ECGs until stable and before discharge 1

Screening in Specific Populations

• First-degree relatives of HCM patients: 12-lead ECG as component of screening algorithm 1
• Preoperative evaluation: Recent ECG recommended in patients with known cardiovascular disease before surgery 1

When ECG is NOT Routinely Indicated (Class III)

• Asymptomatic patients without cardiac risk factors: Guidelines recommend against routine ECG screening even in those with long-term cardiovascular risk 2
• Patients receiving therapy not known to produce ECG changes or affect conditions associated with such changes 1

Critical Interpretation Considerations

Common pitfalls to avoid:

• Always compare current ECG with previous tracings to detect subtle changes 6
• Computerized algorithms can provide erroneous information; physician interpretation is essential 2
• Continuous rhythm monitoring provides less diagnostic information than full 12-lead ECG and may be inadequate 1
• Ensure accurate electrode placement to prevent misdiagnosis 7

The 12-lead ECG remains the most immediately accessible diagnostic tool for cardiac rhythm assessment, detecting arrhythmogenic substrates (Wolff-Parkinson-White, Brugada syndrome, long-QT syndrome, hypertrophic cardiomyopathy), and identifying acute coronary syndromes 1, 8. In hypertrophic cardiomyopathy specifically, the ECG is abnormal in 75-95% of patients, though abnormalities don't reliably correlate with hypertrophy severity 1.