QRS axis validation in clinical electrocardiography.

QRS axis is a key electrocardiographic (ECG) datum in establishing normality and particular diagnoses and is of special concern at the borders of axis ranges for numerous ECG interpretations. Thus, interpreters must be able to recognize gross and small errors in axis determination. This involves the occasional and often inexplicable gross deviation by computers, which should be correct most of the time. This study was undertaken to compare 3 methods of QRS axis calculation and computer interpretation: axes were determined (1) from the bipolar limb leads, (2) from the unipolar limb leads, and (3) from the combination of lead I and lead aVF, which are orthogonal in the Einthoven hexaxial system. In 100 consecutive patients, in whom 87 electrocardiograms were technically clear, there was excellent intermethod agreement for the means, SDs, and interquartile ranges, leaving little to choose from on average. The combination of lead I and lead aVF was best correlated with all the other methods. Because a computer can measure the areas of ECG waves, whereas interpreters necessarily use their amplitudes, hypothetically, the computer is always more accurate. However, computer interpretations are not always available, and physicians regularly interpreting electrocardiograms are aware of axis ranges almost on inspection (especially any algebraically zero, i.e., orthogonal, representation of any lead). They therefore can recognize any serious computer deviations. In conclusion, this investigation indicated that axes calculated from leads I and aVF should be standard to approach precision in initially computing or checking any axis.