Rhythm Recognition, Interpretation, and Reporting
Systematic approach
Read every tracing the same way: rate, regularity, P waves, PR interval, QRS width, then ST-T changes and comparison with prior EKGs. Rate by the large-box method (300 divided by large boxes between R waves gives 300, 150, 100, 75, 60, 50, 43) or by 1500 divided by small boxes. For irregular rhythms, count QRS complexes in a 6-second strip and multiply by 10. Normal PR is 0.12-0.20 s (3-5 small boxes); normal QRS is under 0.12 s (3 small boxes).
Common rhythms
Sinus rhythm requires an upright P in lead II, one P per QRS, and a rate of 60-100. Sinus bradycardia is under 60, sinus tachycardia over 100. Atrial fibrillation is irregularly irregular with no discernible P waves; atrial flutter shows sawtooth flutter waves. PVCs are wide, bizarre, premature, and lack a preceding P wave, usually followed by a compensatory pause. SVT is narrow, fast, and regular; ventricular fibrillation is chaotic; asystole is a flat line. Blocks: first degree has a prolonged PR; Mobitz I shows progressive PR lengthening before a dropped QRS; Mobitz II shows a constant PR with dropped QRS complexes; third degree shows AV dissociation with an escape rhythm.
Ischemia and infarction
ST elevation in contiguous leads suggests injury, often with reciprocal depression elsewhere; ST depression and T-wave inversion suggest ischemia; Q waves suggest older infarction. Territory groups: inferior II, III, aVF; anterior V1-V4; lateral I, aVL, V5-V6.
Reporting
Technicians do not diagnose. Recognize critical findings - rate below 40 or above 150, chest pain with ST elevation, ventricular fibrillation, asystole - notify the responsible provider per policy, document the notification, and stay with the patient.
Traps
The 300 method applied to an irregular rhythm, artifact mistaken for ventricular fibrillation, and PVCs mislabeled as heart block are frequent distractors.
Rule of thumb: rate, regularity, P, PR, QRS, ST-T - and always compare to the prior tracing.