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Pulmonary embolism (acute right heart strain) on a 12-lead ECG

Sinus tachycardia with T inversion in V1-V3 and III together, often an S wave in I, a Q wave in III and an inverted T in III (S1Q3T3).

What to look for

A clot in the lungs loads the right ventricle all at once. The commonest finding is plain sinus tachycardia, and a normal ECG doesn't rule a PE out. The most specific pattern is T inversion in the right-sided chest leads (V1-V4) and in III at the same time. A Q wave in III with an inverted T there and an S wave in I, the famous S1Q3T3, turns up in only about one in five, and it isn't specific either. New RBBB and right axis deviation also fit. In a tachycardic, hypoxic patient, T inversion in V1-V3 that comes with T inversion in III points to the lungs before the coronaries.

Examples

Each is a standard 12-lead: 2.5 seconds of each lead in four columns, with 10 seconds of lead II along the bottom, drawn to scale (25 mm a second, 10 mm a millivolt). The measurements are under each one.

Example 1 · 12-lead · 10 seconds
IaVRV1V4IIaVLV2V5IIIaVFV3V6II25 mm/s · 10 mm/mV
Rate
111/min
Rhythm
RegularSinus: upright in II, biphasic in V1, one before every QRS
PR
0.16 s
QRS
0.09 s, narrow
Axis
43°, normal
QTc
0.40 s
ST up
None
ST down
None
T inverted
III, aVF, V1, V2, V3
Example 2 · 12-lead · 10 seconds
IaVRV1V4IIaVLV2V5IIIaVFV3V6II25 mm/s · 10 mm/mV
Rate
109/min
Rhythm
RegularSinus: upright in II, biphasic in V1, one before every QRS
PR
0.15 s
QRS
0.10 s, narrow
Axis
43°, normal
QTc
0.39 s
ST up
None
ST down
None
T inverted
III, aVF, V1, V2, V3

Don't confuse it with

The ECG tool in the app gives you a new 12-lead every time and walks you through reading it: rate, QRS, axis, then where the ST is up and down. It's part of the Paramedic level, and you can try 5 ECGs a day free.

Try the 12-lead drill

Where the criteria come from

Others in the look-alikes and other findings group