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 300 bpm, with a ventricular rate that is typically 150 bpm (2:1 block) or 100 bpm (3:1 block). Management is similar to AFib — rate control and anticoagulation.
4. Ventricular Tachycardia (VTach): Wide QRS tachycardia (rate >100, QRS >0.12 seconds) with a regular rhythm. The boards test the management: stable VTach (patient is conscious, hemodynamically stable) → amiodarone or lidocaine. Unstable VTach (hemodynamically unstable) → synchronized cardioversion. Pulseless VTach → defibrillation (same as VFib).
5. AV Blocks: The three degrees are high-yield.
- First-degree AV block: Prolonged PR interval (>0.20 seconds) with every P wave followed by a QRS. Benign, no treatment required.
- Second-degree Mobitz I (Wenckebach): Progressively lengthening PR interval until a QRS is dropped, then the cycle repeats. Usually benign, associated with inferior MI or increased vagal tone.
- Second-degree Mobitz II: Fixed PR interval with occasional dropped QRS (no warning). More serious than Mobitz I — can progress to complete heart block. May require pacemaker.
- Third-degree (complete) AV block: No relationship between P waves and QRS complexes. Atria and ventricles beat independently. Ventricular rate is slow (20–40 bpm). Requires emergent pacemaker.
ST Changes: What the Boards Test
ST elevation: The most important finding to recognize. New ST elevation in two or more contiguous leads is STEMI (ST-elevation myocardial infarction) until proven otherwise. The correct management is emergent PCI (percutaneous coronary intervention) — not thrombolytics unless PCI is unavailable within 120 minutes.
ST depression: Associated with NSTEMI, unstable angina, or demand ischemia. Also seen with digoxin toxicity (the classic "scooping" or "Salvador Dali mustache" ST depression).
T wave inversions: Associated with ischemia, PE (right heart strain pattern — S1Q3T3), and ventricular hypertrophy.
QT prolongation: The QTc (corrected QT interval) should be <440 ms in men and <460 ms in women. Prolonged QTc increases the risk of torsades de pointes (a polymorphic VTach). Causes: medications (antipsychotics, antiarrhythmics, macrolides, fluoroquinolones), hypokalemia, hypomagnesemia, hypocalcemia, congenital long QT syndrome.
The Bottom Line
EKG questions on the FNP boards are predictable. Use the five-step systematic approach every time. Know your five rhythms cold: NSR, AFib, atrial flutter, VTach, and AV blocks. Know that hemodynamic instability always changes the management to electrical intervention. Know your ST changes. Master these and EKG becomes one of your most reliable point-earners on the exam.
→ Explore the FNP Board Review Book — EKG interpretation and every high-yield cardiology topic covered with board-focused clinical pearls.