Popular Cardiologist in yelahanka New Town, Bangalore •
ECG interpretation: points to remember
1 ECG reports should be short and based on clinical information where possible.
2 Check that the patient’s name is on the ECG and that the paper speed and
calibration markers are correct.
3 Measure or estimate the heart rate—3 large squares = 100/minute.
4 Establish the rhythm. Look for P waves (best seen in L2). Are the P waves followed
by QRS complexes? Look for anomalously conducted or ectopic beats.
5 Measure the intervals: PR, QRS duration and QT interval (for the latter, consult
tables, but normal is less than 50% of the RR interval).
6 If the QRS complex is wide (> 3 small squares) consider the possibilities: LBBB,
RBBB, WPW or ventricular rhythm or beats. If the pattern is of LBBB, there is
no need in most cases to attempt further interpretation.
7 Estimate the QRS axis. In LAD, L1 and aVF diverge and L2 is predominantly
negative. In RAD, L1 and aVF converge, while L2 matters little. Indeterminate
axis is diagnosed when all six frontal leads are (more or less) equiphasic.
8 Check whether the criteria for LAHB or LAFB have been met.
9 Look for pathological Q waves. In general these are longer than 0.04 seconds
and are more than 25% of the size of the following R wave.
3• AN OVERVIEW OF CLINICAL ELECTROCARDIOGRAPHY 115
10 Increased QRS voltages suggest LVH if:
• the height of the S wave in V1 added to the R wave in V5 or V6 is greater
than 35 mm (SV1 + RV5 or RV6 > 35 mm) or
• any R + S wave height in the V leads is greater than 45 mm or
• the R wave in aVL (RaVL) is greater than 13 mm or
• the R wave in L2 (R2) is greater than 15 mm.
If the ST segment and T wave are affected, it is reported as LVH with ST/T
changes or strain pattern.
In RVH, the R wave is larger than the S wave in V1.
11 Look for ST depression or elevation. ST depression may reflect strain pattern
rather than ischaemia, and ST elevation may be due to early repolarisation or
pericarditis rather than infarction.