Cardiac Rhythm Analysis and Arrhythmias
Two questions solve most strips
Ask whether the rhythm is regular, and whether every QRS is preceded by a P wave with a constant PR interval. That pair separates most answers. Irregularly irregular with no discrete P waves is atrial fibrillation; a regular sawtooth baseline near 300/min is atrial flutter, often conducting 2:1. A regular narrow-complex tachycardia at about 150/min should prompt a search for hidden flutter waves.
Know the block hierarchy: PR >0.20 s is first degree; progressive PR lengthening ending in a dropped beat is Mobitz I; constant PR with sudden dropped beats is Mobitz II; independent P and QRS marching separately is third degree. Mobitz II and third-degree block are the ones that lead to pacing.
Traps: wide-complex tachycardia - assume ventricular tachycardia until proven otherwise; AV dissociation, fusion and capture beats, extreme axis, and concordant precordial patterns favor VT, while aberrancy (AFib with bundle branch block, Ashman phenomenon) is the mimic. A PVC can mimic a dropped beat. Artifact can mimic VT - look at the patient, not just the monitor.
Rule of thumb: if the patient is pulseless or unstable, treat the patient rather than the strip - unsynchronized shock for VF or pulseless VT, synchronized cardioversion for unstable narrow-complex tachycardia.