Role of ECG in Diagnosing and Managing Heart Disease
The electrocardiogram is an essential baseline test required 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:
Multiple ECGs may be required during initial evaluation when conditions evolve rapidly (acute MI) or occur intermittently (anginal attacks, certain arrhythmias). 1
Acute Coronary Syndromes
ST segment elevation with active symptoms indicates acute epicardial artery occlusion with transmural ischemia, requiring emergent reperfusion therapy. 2
ST depression (except in V1-V3) typically indicates subendocardial ischemia from arterial subocclusion, distal embolization, or supply-demand mismatch. 2
Always compare current ECG with previous tracings and obtain serial ECGs when symptom quality or severity changes. 2
Specific Cardiac Conditions
In hypertrophic cardiomyopathy, an abnormal ECG may be the only disease manifestation at early stages and can differentiate HCM from phenocopies like cardiac amyloidosis. 3
The ECG remains the most widely used tool for detecting conditions related to cardiac rhythm abnormalities. 4
Management and Monitoring Applications
Response to Therapy
Serial ECGs are indicated to evaluate short-term and long-term responses to therapy until the disease process and ECG response have stabilized. 1
Specific conditions requiring serial ECG monitoring include:
The frequency of repeat ECGs ranges from minutes to years depending on the specific condition and clinical stability. 1
Medication Monitoring
ECGs should be performed before and during therapy with drugs known to produce significant cardiac effects or ECG changes. 1, 5
High-risk medications requiring ECG monitoring include:
ECG recordings are appropriate after initiation of drug therapy, after changes in therapy, and after addition of interacting drugs with cardiac effects. 1
Post-Procedural Monitoring
Patients undergoing cardioversion (electrical or pharmacologic) should have ECG immediately before, immediately after, and before hospital discharge. 1
After pacemaker insertion or revision, obtain ECG soon after the procedure, after lead threshold maturation, and at periodic intervals throughout the patient's lifetime. 1
More frequent ECGs are indicated with atrial or dual-chamber pacing systems since atrial lead malfunction may not be easily detectable otherwise. 1
After cardiac surgery or extensive pulmonary surgery including transplantation, serial ECGs are recommended until stable and shortly before discharge. 1
Follow-Up Monitoring
Periodic ECGs (e.g., yearly) are appropriate for progressive cardiovascular diseases despite therapy. 1
Symptoms warranting repeat ECG include:
Preoperative Evaluation
A recent preoperative ECG is recommended in all patients with known cardiovascular disease undergoing cardiac or noncardiac surgery due to increased risk for perioperative cardiovascular complications. 1
All patients over 40 years old should have a preoperative ECG, even without suspected cardiac disease. 5
Preoperative ECGs are not indicated for patients under 30 years old with no risk factors for coronary artery disease. 5
Patients being evaluated as transplant donors or recipients should have preoperative ECGs. 5
Screening in Asymptomatic Patients
Baseline ECG is recommended for asymptomatic persons over 40 years of age. 5
Some guidelines recommend baseline ECG at age 20 years with repeats at ages 40 and 60 years. 5
Periodic follow-up (every 1-5 years) is appropriate for patients at increased risk for developing cardiac disease. 5
Guidelines recommend against performing ECG in asymptomatic patients, even with higher long-term cardiovascular risk, as data supporting benefit are not robust. 6
Interpretation Considerations
The responsibility for correct ECG interpretation lies with the physician, who must recognize patient-dependent errors, operator-dependent errors, and artifact. 4
Current ECG tracings should always be compared with previous tracings. 4, 2
A full 12-lead ECG provides more diagnostic information than continuous rhythm monitoring alone. 1
Computerized algorithms exist ubiquitously but can be sources of erroneous information; systematic physician interpretation is essential. 6
Common Pitfalls to Avoid
Ordering "routine" ECGs without clinical indication increases healthcare costs without improving outcomes. 5
Failing to compare with previous ECGs when available may result in misinterpretation of chronic findings as acute changes. 5
Relying solely on computerized interpretation without physician review can lead to diagnostic errors. 6
Inadequate recognition that ST elevation and depression can have nonischemic causes requires clinical correlation. 2