How to Read an EKG for FNP Boards: The 5 Rhythms That Always Appear

Clinical High-Yield · 9 min read · April 28, 2026

EKG questions on the FNP boards intimidate more students than almost any other topic — and they shouldn't. The boards test a very specific, predictable set of EKG findings. They are not asking you to interpret a 12-lead EKG with subtle ST changes in a patient with a complex cardiac history. They are asking whether you can identify the five most common rhythms and know what to do about each one.

Here is the systematic approach and the five rhythms you need to master.

The Systematic Approach: Five Steps Before You Name the Rhythm

Every EKG question should be approached the same way, in the same order. This prevents the most common board mistake: jumping to a conclusion before you have all the information.

Step 1: Rate. Count the R-R intervals. Normal rate is 60–100 bpm. Below 60 is bradycardia. Above 100 is tachycardia. The quick method: divide 300 by the number of large boxes between R waves (each large box = 0.2 seconds).

Step 2: Rhythm. Is it regular or irregular? Are the R-R intervals consistent? Irregular rhythms narrow the differential significantly — the most common cause of an irregularly irregular rhythm is atrial fibrillation.

Step 3: P waves. Are P waves present? Are they upright in lead II? Is there one P wave before every QRS? If P waves are absent or chaotic, think atrial fibrillation. If P waves are present but not followed by a QRS, think AV block.

Step 4: PR interval. Normal is 0.12–0.20 seconds (3–5 small boxes). Prolonged PR = first-degree AV block. Progressively lengthening PR until a QRS is dropped = Mobitz I (Wenckebach). Fixed prolonged PR with occasional dropped QRS = Mobitz II. No relationship between P waves and QRS = third-degree (complete) AV block.

Step 5: QRS width. Normal is <0.12 seconds (3 small boxes). Wide QRS (>0.12 seconds) indicates ventricular origin or aberrant conduction (bundle branch block). Narrow QRS indicates supraventricular origin.

The Five Rhythms You Must Know

1. Normal Sinus Rhythm (NSR): Rate 60–100, regular, upright P waves in lead II, PR interval 0.12–0.20 seconds, narrow QRS. This is the baseline — know it so you can recognize deviations from it.

2. Atrial Fibrillation (AFib): Irregularly irregular rhythm, absent P waves (replaced by chaotic fibrillatory baseline), narrow QRS (unless aberrant conduction). Rate can be rapid (uncontrolled) or controlled. The boards test two things about AFib: rate control (beta-blockers or calcium channel blockers as first-line) and anticoagulation (CHA₂DS₂-VASc score guides anticoagulation — score ≥2 in men, ≥3 in women warrants anticoagulation with a DOAC or warfarin).

Board Pearl: A patient with AFib and hemodynamic instability (hypotension, chest pain, altered mental status) requires immediate synchronized cardioversion — not rate control medications. Hemodynamic instability always changes the answer.

3. Atrial Flutter: Regular rhythm with a "sawtooth" pattern of flutter waves (F waves) at approximately...