EMS Registry ReadyExample 1 · lead V1 · 6 seconds
- Rate
- 61/min6 QRS complexes in 6 seconds × 10 = 60/min
- Rhythm
- Regular
- P waves
- Sinus: upright in II, biphasic in V1, one before every QRS
- P to QRS
- 1:1, a P before every QRS
- PR
- 0.18 s
- QRS
- 0.15 s, wide
Sinus rhythm with left bundle branch block on an ECG strip
A QRS of 0.12 s or more with a deep, broad S (QS or rS) in V1 and a broad R with no Q wave in I, aVL, V5 and V6.
What to look for
The left bundle is blocked, so the septum activates right to left (the small septal q in I, aVL, V5 and V6 disappears) and the left ventricle activates last and slowly. That gives you a broad, often notched R in the lateral leads, peaking more than 60 ms into the QRS, and a deep QS or rS in V1. The ST and T point opposite the QRS (appropriate discordance). Some ST elevation in V1-V3 is expected, generally under a quarter of the S wave before it. What you don't expect is a concordant ST change. That suggests infarction (Sgarbossa).
Examples
Each strip is 6 seconds of lead V1, drawn to scale (25 mm a second, 10 mm a millivolt), so you can count boxes the way you would on paper. Each one is a different example, measured below it.
Example 2 · lead V1 · 6 seconds
- Rate
- 99/min10 QRS complexes in 6 seconds × 10 = 100/min
- Rhythm
- Regular
- P waves
- Sinus: upright in II, biphasic in V1, one before every QRS
- P to QRS
- 1:1, a P before every QRS
- PR
- 0.19 s
- QRS
- 0.13 s, wide
Example 3 · lead V1 · 6 seconds
- Rate
- 75/min7 QRS complexes in 6 seconds × 10 = 70/min
- Rhythm
- Regular
- P waves
- Sinus: upright in II, biphasic in V1, one before every QRS
- P to QRS
- 1:1, a P before every QRS
- PR
- 0.13 s
- QRS
- 0.14 s, wide
Don't confuse it with
- Sinus rhythm with right bundle branch block
A QRS of 0.12 s or more with rSR' (an 'M') in V1-V3 and a wide, slurred S in I, aVL, V5 and V6.
- Sinus rhythm with WPW (pre-excitation)
A short PR (under 0.12 s), a slurred upstroke at the start of the QRS (the delta wave) and a QRS over 0.11 s.
- Anteroseptal STEMI
ST elevation across V1-V4, from an occluded left anterior descending artery.
- LBBB with STEMI (positive Sgarbossa)
In LBBB, ST elevation of 1 mm or more in a lead where the QRS is positive (concordant), which LBBB alone never does.
Want a new strip every time? The ECG Drill in the app draws a fresh, measured example on every try and steers you toward the rhythms you miss. It's part of the Paramedic level, and you can try 5 strips a day free.
Try the ECG Drill