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Identify this rhythm
Analyze both leads and select the correct rhythm.
Lead II: inferior view · Lead V1: septal view · QRS narrow <3 small boxes · Normal PR = 3–5 small boxes
15
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5-Step Approach
① Rate
Regular: 300 ÷ large boxes R-to-R. Irregular: count QRS in 30 large boxes ×10. Normal 60–100.
② Regularity
Equal R-R? Regularly irregular = Wenckebach. Irregularly irregular = AFib.
③ P waves
Present? Upright in II? One P per QRS? No P = AFib, junctional, or ventricular.
④ PR interval
Normal 3–5 small boxes (0.12–0.20s). Prolonged = 1° block. Lengthening then drop = Wenckebach.
⑤ QRS width
Normal <3 small boxes (<0.12s). Wide = BBB, ventricular, paced, or aberrant.
Lead V1 Key Findings
Normal V1: Small r, deep S (rS pattern) · P often biphasic
RBBB: rSR′ (rabbit ears) in V1 · Wide QRS
LBBB: Broad negative QS in V1 · Wide QRS
VTach: All positive or all negative in V1
WPW: Delta wave visible in V1 · Short PR
AFib: Fibrillatory baseline both leads
Brugada: Coved ST elevation V1–V2 · RBBB morphology
RBBB: rSR′ (rabbit ears) in V1 · Wide QRS
LBBB: Broad negative QS in V1 · Wide QRS
VTach: All positive or all negative in V1
WPW: Delta wave visible in V1 · Short PR
AFib: Fibrillatory baseline both leads
Brugada: Coved ST elevation V1–V2 · RBBB morphology
Grid Reference
Small box: 0.04s horizontal · 0.1 mV vertical
Large box: 0.20s horizontal · 0.5 mV vertical
Normal QRS: <3 small boxes (<0.12s)
Normal PR: 3–5 small boxes (0.12–0.20s)
Large box: 0.20s horizontal · 0.5 mV vertical
Normal QRS: <3 small boxes (<0.12s)
Normal PR: 3–5 small boxes (0.12–0.20s)
Common Pitfalls
Wide complex tachycardia = VTach until proven otherwise
AFib vs MAT: MAT has visible (varied) P waves; AFib has none
Mobitz II vs Wenckebach: constant PR (II) vs lengthening PR (Wenckebach)
Fine VFib vs asystole: always confirm in 2 leads before calling asystole
Junctional vs sinus brady: no upright P in Lead II = junctional
New LBBB + chest pain = STEMI equivalent — activate cath lab