Electrocardiographic and Diagnostic Data Interpretation
Systematic ECG interpretation
Read every tracing in the same order: rate, rhythm, axis, intervals, hypertrophy, ischemia or infarction, and comparison with prior tracings. Confirm calibration and lead placement; limb lead reversal produces a negative P and QRS in lead I and can mimic pathology. Calculate rate from the rhythm strip. Determine whether every P has a QRS and every QRS has a P.
Measure PR, QRS, and QT intervals; correct QT for rate. A prolonged PR suggests AV block; a wide QRS suggests bundle branch block, ventricular rhythm, or preexcitation; a prolonged QT raises torsades risk. Evaluate ST segments and T waves in contiguous leads rather than a single lead. ST elevation is not automatically myocardial infarction-consider early repolarization, pericarditis, left ventricular hypertrophy, and aneurysm.
Rhythm traps
An irregularly irregular narrow-complex rhythm without organized P waves is atrial fibrillation. A wide-complex tachycardia should be treated as ventricular tachycardia until proven otherwise. Atrial flutter often shows sawtooth waves with a regular ventricular response. Artifact can mimic ventricular fibrillation; check the patient and leads.
Worked example. A 72-year-old has palpitations. The ECG shows an irregularly irregular narrow-complex rhythm at 130 beats per minute with no clear P waves. This is atrial fibrillation with rapid ventricular response. Look for ischemia, electrolyte abnormalities, and precipitating illness. Rule of thumb: rate, rhythm, axis, intervals, morphology, then compare with a prior tracing. When the rhythm is wide and fast, assume the worst and verify with the patient.