How should an electrocardiogram (EKG) be interpreted and managed in a patient with a history of cardiovascular disease, symptoms such as chest pain or shortness of breath, and risk factors like hypertension, diabetes, or hypercholesterolemia?

EKG Interpretation in Patients with Cardiovascular Disease and Risk Factors

In patients with known cardiovascular disease, symptoms such as chest pain or dyspnea, and cardiovascular risk factors, obtain a 12-lead EKG immediately and ensure it is interpreted by a qualified physician—never rely on computer interpretation alone—while systematically analyzing rate, rhythm, intervals, axis, and ST-T wave changes in the context of the patient's clinical presentation. 1, 2

Immediate Indications for EKG

Class I indications (must obtain EKG):

• Any patient presenting with chest pain, dyspnea, syncope, or near-syncope 1
• Unexplained change in usual pattern of angina pectoris 1
• New or worsening dyspnea 1
• Extreme and unexplained fatigue, weakness, or prostration 1
• Palpitations 1
• Patients with known cardiovascular disease showing any change in symptoms, signs, or relevant laboratory findings 1

Systematic Interpretation Approach

Step 1: Verify Technical Quality

• Confirm proper electrode placement, particularly precordial leads—misplacement is a common source of false diagnoses 2
• Ensure minimum frequency response of 150 Hz for adults (250 Hz for children) to avoid systematic underestimation of signal amplitude 3, 2
• Check for artifacts, baseline wander, and electrical interference before proceeding 2

Step 2: Calculate Heart Rate

• Count QRS complexes in 6-second strip and multiply by 10, or use 300 divided by number of large boxes between R waves 2
• Normal: 60-100 bpm in adults 3, 2
• Bradycardia <60 bpm or tachycardia >100 bpm may be physiologic but require clinical correlation 2

Step 3: Assess Intervals and Conduction

• PR interval: Normal 120-200 ms (3-5 small boxes); prolonged PR suggests AV block 3, 2
• QRS duration: Normal <120 ms (<3 small boxes); widened QRS indicates ventricular conduction delay or bundle branch block 3, 2
• QTc interval: Calculate using Bazett's formula; normal <450 ms (men), <460 ms (women) 3, 2

Step 4: Determine Axis

• Normal axis: +90° to -30° (positive in leads I and aVF) 2
• Left axis deviation: -30° to -90° (positive I, negative aVF) suggests left anterior fascicular block or LVH 2
• Right axis deviation: +90° to +180° (negative I, positive aVF) suggests RVH or left posterior fascicular block 2

Step 5: Evaluate for Ischemia/Infarction

Critical findings requiring immediate action:

• ST elevation: >0.1 mV in limb leads or >0.15-0.2 mV in precordial leads indicates acute injury—refer for emergent reperfusion therapy 2, 4
• Pathological Q waves: >0.04 seconds or >25% of R wave amplitude suggests prior myocardial infarction 2
• Up-sloping ST depression with positive T waves: Increasingly recognized as severe LAD obstruction requiring urgent evaluation 4
• Widespread ST depression with ST elevation in aVR: Represents diffuse subendocardial ischemia from severe multivessel disease—consider urgent angiography if hemodynamically compromised 4

Step 6: Assess for Hypertrophy

• LVH: S in V1 + R in V5 or V6 >3.5 mV (Sokolow-Lyon criteria) 2
• Note that voltage criteria decline with age and vary by population 2

Critical Interpretation Principles

Always Compare with Previous EKGs

• Failure to compare with prior tracings is a common pitfall that misses important interval changes 2
• New findings have different implications than chronic changes 5

Clinical Context is Mandatory

• The same EKG pattern may represent different pathophysiology depending on symptoms 1, 2
• ST-T wave changes are highly sensitive but have low specificity—interpretation requires clinical correlation 1
• Moderate T wave inversion predicts 21% annual mortality with heart disease history versus only 3% without 1

Computer Interpretation Limitations

• Computer-interpreted EKGs without physician verification are not recognized as properly interpreted 1, 3, 2
• Errors in computer interpretation remain common, particularly for rhythm disturbances and ischemia 1, 2
• Computer interpretations serve only as adjuncts, never substitutes for physician review 2

Follow-Up EKG Timing

For patients with known cardiovascular disease:

• Obtain repeat EKG with any change in symptoms, signs, or laboratory findings (Class I) 1
• Periodic EKGs (e.g., yearly) for progressive diseases, with interval determined by disease severity and natural history 1
• Before and after cardioversion procedures 1
• After initiation or changes in cardioactive drug therapy 1

For patients with risk factors but no known disease:

• Baseline EKG for suspected cardiac disease based on symptoms or abnormal findings (Class I) 1
• Periodic follow-up every 1-5 years for patients at increased risk 1

Common Pitfalls to Avoid

• Never interpret EKG findings in isolation—always integrate with clinical presentation, physical exam, and other laboratory data 1, 2
• Avoid equating abnormal T waves solely with ischemia—specificity is low and multiple etiologies exist 1
• Do not miss subtle changes—repeat EKG when symptoms change in severity, as changes may only become apparent with serial recordings 4
• Recognize that interpretation varies even among experts—maintain ongoing education and skill development 1, 2
• Ensure adequate technical quality—inadequate frequency response smooths critical features like Q waves and notched QRS components 3, 2