Assessment Of Electrical Heart Axis Through Comparison Of Hexaxial Reference System With Unipolar And Bipolar Lead Based Formula: Designing Population Spec
Guide By :
Dr Manisha Mandal
Degree :
College :
MGM Medical College & LSK Hospital, Kishanganj, Bihar-855107
The ECG represents the record of the potential fluctuations due to summated action potentials of myocardial fibers during the cardiac cycle. The electrical heart axis (EHA) in the ECG recordings is represented by the mean QRS axis which is the average projection in the frontal plane of the electrical activity vector of ventricular depolarization. The assessment of EHA from net voltages of QRS complexes in bipolar and augmented unipolar leads was carried out in the frontal plane using different formulae: aVF/I, 2aVF/(√3I), (I+2III)/(√3I), √3aVF/(aVL-aVR) and using hexaxial reference system. Comparable results were obtained with aVF/I, 2aVF/(√3I), and (I+2III)/(√3I) for the prediction of normal EHA and Left Axis Deviation (LAD) with 2aVF/(√3I) formula methods showing highest similarity with the hexaxial system. However, none of the formula was suitable for the prediction of Right Axis Deviation (RAD) and Extreme Axis Deviation (EAD). The EHA obtained from the 2aVF/(√3I) leads after applying correction did not differ significantly from the values without correction aVF/I
Methods available for the assessment of electrical axis of the heart include measurement of area under R and S waves in bipolar limb leads, plotting the net voltage of QRS complex on the axis of the leads I and III followed by measuring the angle, both of which are complex and lengthy; inspection of isophasic QRS voltage in six frontal limb leads, inspection of R and S voltages in bipolar limb leads, quadrant method of examination of lead I and lead II or aVF, which have characteristic component of clinically insignificant biasness of about ±100 to ±150 and do not give a precise numeric value. In addition, when there is uncertainty about distinction of left axis deviation assessed by inspection method into either hypertrophy of left ventricles or complete/hemi block of the left bundle branches, accurate measurement of the axis becomes necessary to arrive at the correct diagnosis, thus from clinical and epidemiological point of view, precise determination of the axis is imperative. Determination of mean QRS electrical axes correctly and rapidly would be a valuable clinical aids for the unbiased monitoring of progressive modifications in EHA during the disease sequence, besides investigating the effects of therapeutic actions. Various methods for estimation of EHA must be investigated with huge sample size before being applied for routine practice in ECG machines to avoid misinterpretation of cardiac illness caused by erroneous calculation.
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