A 6-step approach to ECG interpretation
When confronted with an ECG it is important to look at all the important information. In routine clinical practice time is often scarce, and a structured approach might help to perform a quick evaluation.
The following is an example of how one might assess an ECG. As always in medicine, "many roads lead to Rome" and almost everyone develops his/her own approach.
Lets assess the following ECG of a 12 years old female patient:
1) Rhythm: Sinus, atrial ectopic, junctional,...?
Sinus rhythm (P waves upright in inferior leads, preceding every QRS complex)
2) Heart rate: tachycardia or brady for age?
About 55-60 bpm (1 square equals 100ms in a 50mm/s tracing, if you count the squares between the QRS complexes = 1100ms)
3) QRS axis: normal for age? Superior axis? SIQIII,...?
About 80° (from the extremity leads, select the one lead that is most isoelectric (i.e. R and S are equally high) --> in this case lead I; the QRS axis should be perpendicular to the isoelectric lead)
4) PR interval / QRS duration/ QT interval: within normal for age?
PR interval is about 110ms - rather short. However, this may just reflect accelerated AV nodal conduction and is not necessarily pathological.
QRS duration is about 70ms, which is normal.
QT interval equals 420ms. Using Bazett´s formula for heart rate correction the QTc equals QT at a heart rate of 60 bpm.
Step 4 may reveal AV block, long QT syndrome, short QT syndrome, bundle branch block (BBB)...
5) Precordial leads: R/S transition? ST segments? QRS morphology in V1/2?
R/S transition appears in lead V4 - normal.
ST segments show mild J-point elevation in V3/4 with an ascending ST segment - normal in this age group (benign early repolarisation).
QRS morphology in V1/2 shows rS, but no pathologies.
Step 5 may reveal hints for Brugada syndrome (Brugada pattern in V1/2), ARVC (epsilon wave in V1-3), benign early repolarisation (J-point elevation V2-4), LVH/RVH (R/S transition delayed/forwarded).
6) Rhythm strip: premature beats? Pauses? A:V ratio (1:1, 2:1, 1:2,...)?
No premature beats are displayed. Also no pauses.
AV ratio is 1:1.
If a rhythm strip is available (not in this case) it may reveal information on atrial or ventricular premature beats, show pauses (AV block, sinus pause) and may allow for better evaluation of A:V ratio (1:1 in sinus rhythm, 2:1 in AVB,...).