What is the role of an electrocardiogram (ECG) in diagnosing and managing heart disease?

Role of ECG in Diagnosing and Managing Heart Disease

The ECG is an essential and required baseline test for all patients with known or suspected cardiovascular disease, providing immediate diagnostic information about arrhythmias, conduction defects, myocardial infarction, ischemia, chamber enlargement, and other cardiac pathology that cannot be obtained as rapidly with other tests. 1

Diagnostic Applications

Initial Evaluation and Baseline Assessment

• A baseline ECG is mandatory during initial evaluation of any patient with known cardiovascular disease, dysfunction, or arrhythmia. 1

• The ECG provides instantaneous diagnostic information for conditions including:

  • Arrhythmias and conduction defects 1
  • Myocardial infarction and acute ischemia 1, 2, 3
  • Chamber enlargement and myocardial hypertrophy 1
  • Pericardial inflammation 1
  • Electrolyte disturbances 1

• Multiple ECGs may be required during initial evaluation if the condition is rapidly evolving (acute MI) or intermittent (angina, paroxysmal arrhythmias). 1

Acute Coronary Syndrome

• The ECG is the most widely used tool for diagnosis and initial management of acute coronary syndromes. 2

• ST segment elevation with active symptoms indicates acute epicardial artery occlusion requiring emergent reperfusion therapy. 2, 3

• ST depression (except in V1-V3) typically indicates subendocardial ischemia from subocclusion, distal embolization, or supply-demand mismatch 2

• Serial ECGs are essential to assess reversal or progression of acute ischemia and monitor response to thrombolytic or anti-ischemic therapy. 1

• The ECG must be interpreted with clinical context and compared to previous tracings, as ST elevation can occur from non-ischemic causes 2

Management and Monitoring Applications

Response to Therapy

• Serial ECGs are indicated to evaluate short-term and long-term responses to cardiovascular therapy until the disease process stabilizes. 1

• Specific conditions requiring serial ECG monitoring include:

  • Regression/progression of chamber enlargement or hypertrophy 1
  • Resolution of arrhythmias or conduction disturbances 1
  • Pacemaker function assessment 1
  • Myocarditis, pericarditis, endocarditis 1
  • Transplant rejection 1
  • Electrolyte disturbances 1

• The frequency of repeat ECGs ranges from minutes to years depending on the specific condition and clinical stability. 1

Medication Monitoring

• ECGs are required before and during therapy with drugs known to produce significant cardiac effects or ECG changes. 1, 4

• High-risk medications requiring ECG monitoring include:

  • Psychotropic agents (phenothiazines, tricyclic antidepressants, lithium) 1
  • Anti-infective agents (erythromycin, pentamidine) 1
  • Antihypertensive agents (diuretics, ACE inhibitors, calcium channel blockers, beta-blockers) 1, 4
  • Antineoplastic agents 1, 4
  • Cardiac medications (digitalis, dopamine, dobutamine) 1

• ECGs should be obtained after initiation of therapy, after dosage changes, and after addition of interacting drugs. 1

Post-Procedural Monitoring

• ECGs are mandatory just before and immediately after cardioversion, before discharge, and after pacemaker insertion or revision. 1

• Serial ECGs are recommended after cardiac surgery or transplantation until stable and before discharge. 1

• ECGs are indicated after coronary angioplasty or intracardiac invasive procedures until the condition stabilizes 1

Patient Population-Specific Indications

Symptomatic Patients

• Patients with cardiac symptoms (chest pain, dyspnea, palpitations, syncope) should have an ECG performed. 4, 5

• Specific symptoms warranting repeat ECG include:

  • Syncope or near-syncope 1, 4
  • Unexplained change in angina pattern 1
  • New or worsening dyspnea 1, 4
  • Extreme unexplained fatigue, weakness, prostration 1, 4
  • Palpitations 1, 4

Preoperative Assessment

• All patients with known cardiovascular disease undergoing cardiac or non-cardiac surgery require a recent preoperative ECG. 1, 4

• All patients over 40 years old should have a preoperative ECG, even without suspected cardiac disease. 4

• Preoperative ECGs are not indicated for patients under 30 years old without coronary artery disease risk factors 4

Asymptomatic Patients

• Baseline ECG is recommended for asymptomatic persons over 40 years of age. 4

• Periodic follow-up ECGs (every 1-5 years) are appropriate for patients at increased risk for developing cardiac disease. 4

• Guidelines recommend against performing ECGs in asymptomatic patients without higher cardiovascular risk, as data supporting benefit are not robust. 5

Critical Interpretation Considerations

Technical Requirements

• A full 12-lead ECG is required for accurate interpretation; continuous rhythm monitoring alone may be inadequate. 1

• Additional leads may be necessary in children and selected adults 1

Interpretation Pitfalls

• Current ECG tracings must always be compared with previous tracings to avoid misinterpreting chronic findings as acute changes. 4, 6

• Computerized algorithms can be sources of erroneous information; physician interpretation is essential. 6, 5

• Physicians must recognize patient-dependent errors, operator-dependent errors, and artifact 6

• A systematic, methodical approach to ECG analysis ensures accurate interpretation. 6, 5

Clinical Context

• The ECG must be read along with clinical assessment of the patient. 2

• Knowing the clinical scenario and comparing subsequent ECGs when symptoms change aids diagnosis in difficult cases 2

Cost-Effectiveness Considerations

• Ordering "routine" ECGs without clinical indication increases healthcare costs without improving outcomes. 4

• The routine baseline ECG has little value for future emergency comparison when patients later experience acute cardiac symptoms 7

• For patients with equivocal clinical and ECG findings, a baseline ECG might help avoid unnecessary hospitalization in only 4.7% of cases 7