How do I learn to interpret an electrocardiogram (ECG) for a patient with a history of requiring pain management, potentially on nonsteroidal anti-inflammatory drugs (NSAIDs) like diclofenac?

Learning ECG Interpretation: A Structured Approach

Begin by mastering the systematic method of ECG analysis through supervised bedside interpretation during residency training, supplemented by self-study texts, with competency demonstrated through board certification and ACLS training. 1

Foundational Training Requirements

Core Learning Environment

• Obtain hands-on experience interpreting ECGs at the bedside in both ambulatory and inpatient settings under expert supervision. 1
• Utilize specialty rotations that incorporate structured ECG self-study materials combined with direct feedback from experienced electrocardiographers. 1
• Focus on understanding the physiological basis of ECG generation rather than relying solely on pattern recognition—this includes cardiac anatomy as it relates to the ECG, how different leads view the heart, and how normal waveforms are formed. 2

Understanding ECG Technology

• Learn how modern digital ECG systems acquire and process signals, as automated measurements and computer-generated interpretations now dominate practice. 1
• Recognize that different automated systems may produce significant differences in amplitude and interval measurements, requiring you to understand the underlying principles rather than blindly accepting computer interpretations. 1
• Master proper lead placement and recording methods, as technical errors during acquisition (incorrect limb or precordial lead placement, artifacts, inadequate filtering) can produce misleading patterns. 1, 3

Systematic ECG Interpretation Framework

The 10-Minute Rule for Acute Presentations

• In any patient presenting with chest pain, obtain an ECG within 10 minutes of presentation. 4
• Immediately identify ST-segment elevation, which indicates complete coronary artery occlusion in 80-90% of cases and mandates reperfusion therapy within 30 minutes. 5
• Recognize ST-segment depression or T-wave inversions as markers of subendocardial ischemia requiring serial troponin measurements and continuous monitoring. 5

Critical Limitation You Must Never Forget

• A single normal ECG never rules out acute coronary syndrome—up to 6% of patients with evolving ACS are discharged with normal ECGs, and only 30-40% of acute MI patients initially show ST-elevations. 4, 5
• Left ventricular hypertrophy, bundle branch blocks, and ventricular pacing can mask ischemic changes. 1, 4
• One-third of patients with acute chest pain have normal admission ECGs, yet 5-40% of these develop myocardial infarction. 5

Serial ECG Strategy

• Perform repeat ECGs immediately when chest pain recurs, persists, or when clinical condition deteriorates. 4
• Continue serial ECGs every 15-30 minutes during the first hour if symptoms persist, as ischemic changes evolve over time. 6
• Always compare current ECGs with previous tracings when available—a normal but changed ECG may reveal subtle new abnormalities. 1, 4

Supplemental Lead Techniques

• Use posterior leads (V7-V9) when clinical suspicion for ACS remains intermediate-to-high despite a nondiagnostic standard ECG, as left circumflex or right coronary artery occlusions causing posterior wall ischemia are often "electrically silent" on standard 12-lead recordings. 1, 4

Integration with Clinical Context

The Role of Clinical History

• Cardiologists demonstrate greater accuracy than noncardiologists in ECG interpretation when minimal clinical history is provided, and noncardiologists are more affected by clinical context and automated interpretations. 1
• Read the ECG alongside clinical assessment—ST-segment changes must be interpreted in the context of active symptoms, previous ECGs, and subsequent tracings. 7
• Recognize that ST-segment elevation can occur from nonischemic causes, and ST-depression may result from left ventricular hypertrophy or cardiomyopathies rather than ischemia. 7

Biochemical Marker Integration

• Always combine ECG interpretation with serial cardiac troponin measurements, as troponin is the most sensitive test for myocardial injury. 4, 5
• A single troponin drawn less than 6 hours from symptom onset may miss injury and should never be used alone to exclude ACS. 5, 6
• Repeat troponin at 6-12 hours from symptom onset to detect rising or falling patterns. 5, 6

Competency Assessment and Maintenance

Demonstrating Competency

• Achieve basic competency through internal medicine residency completion, board certification (which includes ECG interpretation questions), and ACLS training. 1
• For interpreting ECGs when unfamiliar with the patient's clinical context, additional proficiency documentation through experience or standardized testing may be necessary beyond basic residency training. 1

Maintaining Skills

• Engage in continuing medical education through seminars or self-assessment programs, particularly if you read ECGs infrequently. 1
• Uncontrolled studies show improved short-term performance on ECG examinations following structured instruction, though the optimal volume of ECG interpretations needed to maintain competency remains uncertain. 1

Common Pitfalls to Avoid

• Never discharge a patient with ongoing chest pain or high clinical suspicion for ACS based solely on a single normal ECG—this is the most dangerous error in chest pain evaluation. 4
• Do not delay repeat ECGs waiting for scheduled intervals if symptoms change; symptom-driven timing takes priority. 4
• Avoid relying on automated computer interpretations without understanding the underlying physiological principles and technical limitations. 1, 8
• Do not overlook technical acquisition errors that can mimic or mask pathology. 3

Special Consideration for NSAID Users

While diclofenac and other NSAIDs are associated with cardiovascular adverse effects, the ECG interpretation principles remain identical. 9 Focus on detecting ischemic changes through the systematic approach outlined above, recognizing that NSAID use may increase the clinical suspicion for cardiovascular events in appropriate contexts.