A new method to determine the QRS axis—QRS axis determination

Abstract Background The development of a perfect method for determining the mean QRS axis (ÂQRS) is still lacking. Hypothesis We proposed a new simple method, whether this method is accurate is unknown. Methods The axis perpendicular to the mean QRS axis (P‐ÂQRS) divides six limb leads into two groups. All the leads that are in the range of 180° along the ÂQRS are positive, while all the leads in another 180° are negative, one lead is isodiphasic if it is on the P‐ÂQRS. If no lead is isodiphasic, then the P‐ÂQRS is located in the middle of two adjacent leads, which can help us determine the P‐ÂQRS. The six limb leads that fall in the range of −30° to 120° are as follows: aVL (−30°), I (0°), −aVR (30°), II (60°), aVF (90°), and III (120°). We can check an external lead (aVL or III) first. For example, if lead III is isodiphasic and lead aVF is positive, the P‐ÂQRS is 120°; if lead III is negative and lead aVF is positive, then the P‐ÂQRS is 105°. If more than one lead is negative, all such leads can be checked individually until a positive or isodiphasic lead is found. The ÂQRS can be easily decided once we know the P‐ÂQRS. In total, 200 recorded ECGs were investigated. We obtained the ÂQRS from our new method, computer interpretations, and a standard bipolar method. The Pearson correlation coefficient and Bland‐Altman analysis were performed. Results The mean and SDs were remarkably similar, the correlation coefficient between the P‐ÂQRS method and the bipolar method was 0.976 (P < .001). Mean bias (Bland‐Altman limits of agreement) between the two methods was 0.885 (−12.37 to 14.14). Conclusion The new method is simple and is able to assess the mean QRS axis accurately.

Electrocardiograms (ECGs) are the recording of cardiac electrical activity. The axis of an ECG is the major direction of the overall electrical activity of the heart, which can be determined by analyzing the magnitude and size of the QRS complex of the limb leads. Existing methods for determining the mean QRS axis (ÂQRS) are either complicated requiring calculation, or simple but lack of accuracy. 1 Some convenient methods have been provided in recent years, but they are still too complicated to be widely used. 2 In a clinical context, if only the approximate range of ÂQRS is required, the ÂQRS can be assessed by leads I and aVF. If both leads are positive, the ÂQRS is normal (from 0 to 90 ). The method of determining the electrocardiogram axis by isodiphasic lead (isodiphasic lead method) has been popular for half a century, since Grant raised it. 3 In this method, the ÂQRS is perpendicular to the isodiphasic lead. However, this method cannot be used if none of the leads exhibits an isodiphasic lead. We have optimized this method and made it suitable for all electrocardiographs.

| METHODS
The axis perpendicular to the mean QRS axis (P-ÂQRS) divides six limb leads into two groups. All the leads in a 180 range along the ÂQRS are positive, while all the leads in a 180 range against the ÂQRS are negative, one lead is isodiphasic if it is on the P-ÂQRS. If no lead is isodiphasic, then the P-ÂQRS is located in the middle of two adjacent leads. The six limb leads that fall in the range of −30 to 120 are as follows (referred to as the Cabrera sequence 4 ): aVL (−30 ), I (0 ), −aVR (30 ), II (60 ), aVF (90 ), and III (120 ) (Figure 1).
When the ÂQRS is at +45 , the morphology is positive in all the leads (aVR is negative, meaning that −aVR is positive), because the main vector of the mean QRS axis falls within the positive hemifield of all leads (with the exception of aVR). When the ÂQRS shifts to the left from +45 to +30 and as far as −120 , the P-ÂQRS shifts from 135 to 130. Up to −30, the QRS complexes become negative, starting with lead III, changing from positive to isodiphasic and then from isodiphasic to negative for each shift in the ÂQRS of 15 left (Table 1A). As the ÂQRS shifts to the right from +45 to +60 and up to 180 , the complexes again become negative, but starting with lead aVL, they change from positive to isodiphasic and then from isodiphasic to negative with every 15 shift to the right in the electrical axis (Table 1B). When the mean QRS axis changes, the morphology of leads around the P-ÂQRS changes; this allows us to easily determine the P-ÂQRS from the morphology of limb leads. In most cases, the majority of leads are positive, making it easier to identify the P-ÂQRS starting with a negative lead. We can first check whether an external lead (aVL or III) is negative or isodiphasic; if more than one lead is negative, all of these leads can be checked individually until a positive or isodiphasic lead is found. For example, if lead III is isodiphasic and lead aVF is positive, the P-ÂQRS is 120 (the other measurement, −60 , is disregarded). If lead III is negative and lead aVF is positive, the P-ÂQRS is located in the middle of them, that is, at 105 . If lead aVF is isodiphasic, the P-ÂQRS is 90 . If it is negative, lead II is examined. The rest of the leads can be evaluated in the same way.
Once the P-ÂQRS is determined, it is easy to determine the ÂQRS. We approached determining ÂQRS in the following way: The morphology of limb leads and the P-ÂQRS, ÂQRS Abbreviations: ÂQRS, the mean QRS axis; P-ÂQRS, The axis perpendicular to the mean QRS axis; !, isodiphasic; ", positive; #, negative; A, the lead is not positive from lead III; B, the lead is not positive from aVL. 2. If lead III is isodiphasic or negative, the degree of the P-ÂQRS minus 90 is the degree of the ÂQRS.
3. If lead aVL is isodiphasic or negative, the degree of the P-ÂQRS plus 90 is the degree of the ÂQRS.
If lead aVL is isodiphasic, lead I is positive, the PP-ÂQRS is −30 (the other measurement, 150 , is disregarded), and the ÂQRS is 60 . If lead aVL is negative, lead I is positive, the P-ÂQRS is located in the middle-that is, at −15 , and the ÂQRS is 75 . If lead I is isodiphasic, the P-ÂQRS is 0 , and the ÂQRS is 90 . If it is negative, lead aVR is examined. The rest of the leads can be evaluated in the same way.
Using this procedure, the ÂQRS may be calculated with a precision of 15 . We

| RESULTS
We reviewed the standard 12 lead electrocardiograms of 200 patients.  Table 2. The correlation coefficient between the P-ÂQRS method and the bipolar method was 0.976 (P < .001). The correlation coefficient between the bipolar method and the computer calculations was 0.931 (P < 0.001).
The maximum difference between the P-ÂQRS method and the bipolar method was 25 , and the maximum difference between the computer calculations and the bipolar method was 69 . The Bland-Altman plot showed the mean bias ± SD between the P-ÂQRS method and the bipolar method as 0.885 ± 6.761, and the limits of agreement were −12.37 and 14.14 ( Figure 2).
In the analysis of the ÂQRS, both amplitude and area require con- The Bland-Altman plot of differences between the P-ÂQRS and bipolar methods shows the mean bias ±SD (0.885 ± 6.761) and the limits of agreement (−12.37 and 14.14) measurements are only accurate to within 30 . This method is similar to our method; however, we provided a faster determination.
As anticipated, our study indicated all three methods showed excellent agreement. The bipolar approach is considered to be the most reliable, the correlation coefficient of the bipolar approach and the P-ÂQRS technique is 0.976. In the majority of situations, the disparity between the two methods is 0 to 15 , but in a few cases, the disparity is 15 to 25 .
The Bland-Altman comparison method demonstrates the consistency of the bipolar and P-ÂQRS methods. The two ECGs with the most significant differences had a wide S-wave in lead III. When identifying the electric axis, waveform area must be considered in addition to amplitude; however, measuring the waveform area using the bipolar method proved difficult, so we opted to measure the ÂQRS with leads I and II, which reduced the difference significantly. The P-ÂQRS of one ECG was −15 , 10 using the bipolar method and when mea-

| Limitations
Only 240 ECGs were analyzed; however, the utilization of the P-ÂQRS to determine the ÂQRS is a mature method that does not need widespread testing.

| Summary
At present, there are numerous methods for analyzing the QRS axis, none of which is perfect. We used the new method to quickly and accurately determine the QRS axis-this method is easier to navigate and is worthy of clinical application.

ACKNOWLEDGMENTS
This research was supported by General science and technology projects of Jingmen Science and Technology Bureau.
F I G U R E 3 An ECG of a right bundle branch block, lead aVL is negative, lead I is negative, lead aVR is isodiphasic with a wide R-wave