Quick method for mean frontal QRS axis determination.
BACKGROUND
ECGs are the recording of the electrical activity of the heart. The direction of it's current in the frontal plane can be determined by analyzing the QRS direction and magnitude in limb leads. Several methods for determination of the QRS frontal axis have been proposed, however most of them require memorization of the exact location of the leads in the frontal plane with pen and paper calculations.


METHODS
a new method of estimating the frontal mean QRS axis in the standard 12 lead ECG is proposed. This method consists of assigning pre-determined values to each frontal lead in ECGs, which have a positive or isoelectric QRS complexes in lead, I. The mnemonic "+/- 90, -30, +30, -60, +60, and 0" is obtained by plotting only the value of the axis which is perpendicular to the each lead on the left side of the hexaxial system. The right-sided perpendiculars are not considered since lead I indicates a left sided axis. The most isoelectric lead will have only one value plotted and that will be the mean QRS axis in the frontal plane. By finding the most equiphasic lead(s) and matching the corresponding pre-determined value we can estimate the frontal mean QRS axis in most of the cases. Interpolation between two leads is allowed if no single isoelectric lead is identified. We reviewed the standard 12 lead electrocardiograms of 155 patients who underwent open-heart coronary revascularization procedures at the VA Caribbean Health Center from 2003 to 2006. Frontal mean QRS axis was determined by the proposed new methodology and the results were compared to the QRS axis determined by the GE Marquette 5000 electrocardiographer utilized in all the reviewed ECG's. Simple regression analysis was used to determine the proposed methods predictive accuracy.


RESULTS
We obtained a high coefficient of determination R2= 0.9505, p<0.001. The derived linear equation was obtained as follow: y = 1.0007 + 0.9580x (Where independent x= QRS axis estimated by the new method, dependent y = QRS axis estimated by ECG machine).


CONCLUSIONS
The proposed new method is simple and is able to estimate accurately the ECG frontal axis as compared with the GE Marquette 5000 electrocardiographer in most of the cases.
Martinez-Diaz
Jorge
J
Cardiology Section, VA Caribbean Healthcare System, One Veterans Plaza,10 Casia St., San Juan, PR 00921-5800, USA. Jorge.Martinez-Diaz@med.va.gov
Escabi-Medoza
Jose
J
Oviedo
Raúl
R
Acevedo
Javier
J
D000293:Adolescent; D000328:Adult; D000367:Age Factors; D000465:Algorithms; D002037:Bundle-Branch Block / Q000175:diagnosis; D002648:Child; D002675:Child, Preschool; D004562:Electrocardiography / Q000379:methods*; D004566:Electrodes; D006801:Humans; D017379:Hypertrophy, Left Ventricular / Q000175:diagnosis; D007223:Infant; D009203:Myocardial Infarction / Q000175:diagnosis; D012044:Regression Analysis