What is the interpretation of this ECG (electrocardiogram) for an adult patient with an unknown medical history?

ECG Interpretation: Systematic Approach

I cannot interpret your specific ECG without seeing the actual tracing, but I can provide you with the systematic framework recommended by major cardiology societies to interpret any ECG accurately.

Immediate Technical Verification

Before interpreting any ECG, you must first verify the technical quality of the recording to avoid diagnostic errors. 1, 2

• Check electrode placement accuracy – misplaced precordial leads are among the most common sources of false diagnoses and can significantly alter your interpretation 1, 2
• Verify adequate filtering settings – ensure minimum high-frequency response of 150 Hz for adults to maintain diagnostic precision 1
• Identify artifacts – look for baseline wander, electrical interference, or muscle tremor that could distort waveforms 1, 2
• Never accept computer interpretation without physician verification – automated systems still produce frequent errors and are not recognized as properly interpreted ECGs without qualified physician review 3, 1, 2, 4

Systematic Interpretation Framework

Step 1: Rate and Rhythm Analysis

• Calculate heart rate by counting QRS complexes in a 6-second strip and multiplying by 10, or use 300 divided by the number of large boxes between consecutive R waves 1, 2
• Normal sinus rhythm: 60-100 bpm with P wave before each QRS and consistent PR interval 1, 2
• Identify rhythm irregularities – premature beats, pauses, or completely irregular patterns suggesting atrial fibrillation 1, 2

Step 2: Intervals and Conduction

• PR interval: Normal 120-200 ms; prolonged PR suggests AV block 1, 2
• QRS duration: Normal <120 ms; widened QRS indicates ventricular conduction delay or bundle branch block 1, 2, 5
• QTc interval: Calculate using Bazett's formula; normal <450 ms (men) or <460 ms (women); prolongation increases risk of sudden death 1, 2

Step 3: Axis Determination

• Normal axis: Both leads I and aVF positive (+90° to -30°) 1, 2
• Left axis deviation: Lead I positive, aVF negative (-30° to -90°) 1, 2
• Right axis deviation: Lead I negative, aVF positive (+90° to +180°) 1, 2

Step 4: Morphology Assessment

• P waves: Should be present and upright in leads I, II, aVF for normal sinus rhythm 5
• Q waves: Pathological if >0.04 seconds duration or >25% of R wave amplitude in two contiguous leads (excluding III and aVR) 1, 5
• R wave progression: Should increase from V1 to V5/V6 5
• T waves: Should be upright in leads I, aVL, V5, V6 in adults; inversion ≥1 mm in two contiguous leads is abnormal (excluding aVR, III, V1) 5

Step 5: ST Segment and Ischemia Evaluation

This is the most critical step for identifying life-threatening conditions requiring immediate intervention. 2, 6

• ST elevation: >0.1 mV in limb leads or >0.15-0.2 mV in precordial leads indicates acute injury requiring emergent reperfusion 1, 2, 6
• ST depression: ≥0.5 mm in two contiguous leads suggests subendocardial ischemia 5, 6
• Note the location of ST changes to determine affected coronary territory for catheterization lab activation decisions 1, 2
• Distinguish early repolarization (benign variant with J-point elevation ≥0.1 mV, concave ST elevation, peaked T waves) from pathological ST elevation 3, 5

Critical Clinical Integration

The ECG must never be interpreted in isolation from the clinical presentation. 3, 1, 2, 6

• The same ECG pattern can occur in completely different pathophysiologic states 3, 6
• Clinical signs and symptoms alone have insufficient sensitivity (35-38%) and specificity (28-91%) without ECG correlation 2
• Always compare with previous ECGs when available – dynamic changes are often more significant than isolated findings 1, 2
• ST-segment and T-wave changes are the most sensitive but least specific ECG abnormalities 3

Age and Population-Specific Considerations

• Athletes: Sinus bradycardia ≥30 bpm, early repolarization in 50-80%, and voltage criteria for LVH are normal variants 3, 1
• Black athletes: Right precordial T-wave inversion in V2-V4 with ST elevation is a physiological pattern 3
• Children and adolescents: T-wave inversion in anterior leads may be normal under age 16 5
• Neonates: Normal axis ranges 55-200° at birth, decreasing to ≤160° by 1 month 3

Common Pitfalls to Avoid

• Do not over-rely on voltage criteria alone for chamber enlargement – sensitivity is only 11.2% for LVH using combined criteria 1
• Do not equate abnormal T waves with ischemia – specificity is low, and T-wave inversion predicts 21% annual mortality with heart disease but only 3% without 3
• Do not miss technical errors – inadequate high-frequency response causes systematic underestimation of signal amplitude and smoothing of Q waves 1
• Do not fail to consider nonischemic causes of ST elevation (pericarditis, early repolarization, Brugada syndrome) or ST depression (LVH, cardiomyopathy) 3, 6

When Computer Interpretation Shows "Normal" or "Otherwise Normal"

Recent evidence suggests that computer interpretations of "normal" or "otherwise normal" have 100% negative predictive value for STEMI in emergency department triage patients 4. However, physician verification remains mandatory because computer algorithms frequently misinterpret rhythm disturbances, ischemia patterns, and subtle abnormalities 3, 1, 2.

Maintaining Competency

• Minimum training requirement: Interpretation and review of 800 ECGs within a 3-year period under experienced supervision 3
• Continuing education: Regular seminars or self-assessment programs are essential for physicians who read ECGs infrequently 1, 2
• Interpretation variability exists even among expert electrocardiographers, emphasizing the need for ongoing skill maintenance 1