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Sinus rhythm with PJCs on an ECG strip

An early narrow QRS with no sinus P before it, and an inverted P just before, inside or just after it.

What to look for

Early narrow QRS complexes, shaped like the sinus ones, with no sinus P before them. The impulse also travels back up into the atria, so you get an inverted P in II just before the QRS (PR under 0.12 s), hidden inside it, or just after it. Is the pause afterward compensatory? That depends on whether that P resets the sinus node, and the key says which.

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
87/min underlyingThe whole strip averages 86/min · 9 QRS complexes in 6 seconds × 10 = 90/min
Rhythm
Regular underneath, with early beats breaking it
P waves
Sinus P waves; an inverted P just before each PJC
P to QRS
1:1 for the sinus beats; each PJC's inverted P comes just before its QRS, too close to have conducted it
PR
0.18 s
QRS
0.07 s, narrow
PJCs
2 on this strip
Example 2 · lead II · 6 seconds
II25 mm/s · 10 mm/mV
Rate
73/min underlyingThe whole strip averages 75/min · 7 QRS complexes in 6 seconds × 10 = 70/min
Rhythm
Regular underneath, with early beats breaking it
P waves
Sinus P waves; none with the PJCs
P to QRS
1:1 for the sinus beats; the PJCs have no visible P
PR
0.13 s
QRS
0.10 s, narrow
PJCs
2 on this strip
Example 3 · lead II · 6 seconds
II25 mm/s · 10 mm/mV
Rate
75/min underlyingThe whole strip averages 80/min · 9 QRS complexes in 6 seconds × 10 = 90/min
Rhythm
Regular underneath, with early beats breaking it
P waves
Sinus P waves; an inverted P just before each PJC
P to QRS
1:1 for the sinus beats; each PJC's inverted P comes just before its QRS, too close to have conducted it
PR
0.14 s
QRS
0.10 s, narrow
PJCs
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 Junctional group