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Sinus arrest on an ECG strip

Regular sinus rhythm, then a pause of over 3 seconds that is not a whole number of P-P cycles.

What to look for

Regular sinus rhythm, until the sinus node stops. You get no P wave and no QRS for over 3 seconds, then sinus beats start again. Measure the pause: it isn't a whole number of P-P cycles. That's how you tell it from sinoatrial exit block, where a P drops out and the next one arrives exactly on time.

Examples

Each strip is 6 seconds of lead II, 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 1 · lead II · 6 seconds
II25 mm/s · 10 mm/mV
Rate
71/min underlyingThe whole strip averages 33/min · 4 QRS complexes in 6 seconds × 10 = 40/min
Rhythm
Regular, except for the pause
P waves
Upright in II, uniform; none during the pause
P to QRS
1:1, a P before every QRS; during the pause, neither
PR
0.13 s
QRS
0.09 s, narrow
Example 2 · lead II · 6 seconds
II25 mm/s · 10 mm/mV
Rate
80/min underlyingThe whole strip averages 36/min · 4 QRS complexes in 6 seconds × 10 = 40/min
Rhythm
Regular, except for the pause
P waves
Upright in II, uniform; none during the pause
P to QRS
1:1, a P before every QRS; during the pause, neither
PR
0.18 s
QRS
0.10 s, narrow
Example 3 · lead II · 6 seconds
II25 mm/s · 10 mm/mV
Rate
73/min underlyingThe whole strip averages 33/min · 4 QRS complexes in 6 seconds × 10 = 40/min
Rhythm
Regular, except for the pause
P waves
Upright in II, uniform; none during the pause
P to QRS
1:1, a P before every QRS; during the pause, neither
PR
0.17 s
QRS
0.10 s, narrow

Don't confuse it with

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

Where the criteria come from

Others in the Sinus group