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Sinus rhythm with PACs on an ECG strip

Sinus rhythm with early beats that start with an early P wave of a different shape, then a narrow QRS.

What to look for

Sinus rhythm with early beats. Each one starts with an early P wave of a different shape (here smaller and more pointed), followed by a normal QRS. That early P resets the sinus node, so the pause after a PAC is less than compensatory: the beats on either side of it are less than two sinus cycles apart.

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
65/min underlyingThe whole strip averages 66/min · 7 QRS complexes in 6 seconds × 10 = 70/min
Rhythm
Regular underneath, with early beats breaking it
P waves
Sinus P waves, plus early P waves of a different shape (the PACs)
P to QRS
1:1; each PAC's early P is followed by its own QRS
PR
0.12 s
QRS
0.10 s, narrow
PACs
2 on this strip
Example 2 · lead II · 6 seconds
II25 mm/s · 10 mm/mV
Rate
88/min underlyingThe whole strip averages 90/min · 9 QRS complexes in 6 seconds × 10 = 90/min
Rhythm
Regular underneath, with early beats breaking it
P waves
Sinus P waves, plus early P waves of a different shape (the PACs)
P to QRS
1:1; each PAC's early P is followed by its own QRS
PR
0.14 s
QRS
0.09 s, narrow
PACs
2 on this strip
Example 3 · lead II · 6 seconds
II25 mm/s · 10 mm/mV
Rate
61/min underlyingThe whole strip averages 64/min · 7 QRS complexes in 6 seconds × 10 = 70/min
Rhythm
Regular underneath, with early beats breaking it
P waves
Sinus P waves, plus early P waves of a different shape (the PACs)
P to QRS
1:1; each PAC's early P is followed by its own QRS
PR
0.14 s
QRS
0.09 s, narrow
PACs
2 on this strip

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 Atrial group