ABC of clinical electrocardiography

Introduction. I—Leads, rate, rhythm, and cardiac axis

BMJ 2002; 324 doi: http://dx.doi.org/10.1136/bmj.324.7334.415 (Published 16 February 2002)
Cite this as: BMJ 2002;324:415

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Cardiac axis at the frontal plane can be calculated with precision using this easy rule:

1. When electric axis is oriented at +60°, complexes are positive at DI, DII and DIII, with a maximal value at DII (vector is parallel to it).

2. From this startpoint, left deviation begins changing complexes at DIII, that become isodiphasic at first (zero value, vector is perpendicular) when the axis at +30°, and then negative at 0°. After this, DII will change in a similar way, and after will change DI.

3. Axis right deviation begins modifying complexes at DI in a similar way, being isodiphasic at +90° and negative at 120°, and so on with DII and DIII.

Then, the general rule will be:

-start at +60°, with positive complexes.

-when changes begin at DIII, you must subtract 60° for every negative complex and 30° for every isodiphasic one.

-when changes begin at DI, you must add these same values.

With this rule in mind, it can be easily seen that in the published example, cardiac axis is:

60 – 60 = 0 (DIII negative) 0 – 30 = -30° (DII isodiphasic)

So, an axis with negative values at DI and DII will be located at ±180° ( = 60 + 60 + 60).

When DI is negative and DII isodiphasic, axis will be at +150° ( = 60 + 60 + 30).

When DIII and DII are negative, it will be at –60° ( = 60 – 60 – 60).

This rule is a rational and a logical one; it’s easy to remember, only (almost don’t) requires to know lead locations at hexaxial system. Moreover, you can reach a higher precision (changes lesser than 30°) looking at morphologies in monopolar leads (aVL, aVR and aVF), or at the same bipolar leads; for example, if DIII is negative, and DII diphasic with S > R, you can calculate an axis at -40°.

Competing interests: None declared

Antonio Baroja, M.D., Ph.D., Prof. of Human Physiology

J.M. Gandarias, F. Ainz, J.J. Goiriena, and E. Sabino,

Dpt. of Physiology. Fac. of Medicine and Dentistry. Basque Country University. 48940 Leioa. Spain.

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As far as "condition" is not restricted to "disease", in my opinion, the most prevalent condition in which determination of the axis of the QRS -complex is useful is in diagnosing the reversal of arm electrodes.

A negative QRS-complex in lead I is in my adult cardiology practice most often due to a reversal of arm electrodes.

Competing interests: None declared

Hans JM Van Brabandt, cardiologist

B2800 Mechelen Belgium

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TAKE LEAD L-1 AND LEAD L-11,PLACE L-11 BELOW L-1 IF QRS COMPLEXES ARE POINTING TO EACH OTHER ,IN OTHER WORDS THEY SEEM TO BE TOUCHING, MEANS TRYING TO SHAKING HANDS WITH EACH OTHER,IT MEANS RT.AXIS,AS WE SHAKE HANDS WITH RIGHT HANDS.SIMILARLY IF THE QRS COMPLEXES ARE GOING AWAY FROM EACH OTHER,IT MEANS IT IS LEFT AXIS.AND IF BOTH COMPLEXES ARE GOING IN THE SAME DIRECTION,IN OTHER WORDS THERE IS POSITVE DIRECTION OF QRS COMPLEXES IN BOTH LEADS,THEN THERE IS NO AXIS DEVIATION.

Competing interests: None declared

UMESH K. MALHOTRA, FAMILY PHYSICIAN

DELHI-110012

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22 February 2002

Meek & Morris provide a good introduction to the study of electrocardiography. However, perhaps an easier way of determining the cardiac axis is this.

Leads I and aVF are at right angles. Knowing this, one can add the vectors provided by the ECG. If the QRS complexes are positive overall in both leads, the axis must be normal; and if positive in aVF and negative in I, the axis is rightward. However if the axis is negative in aVF and positive in I, the axis may be normal (up to -30 degrees)but needs a little more calculation, though a small I and very negative aVF implies a leftward axis.

Incidentally, considering the limb leads gives not only a marker of the territory involved but also of the likely artery supplying that territory. Thus II/III/aVF, being inferior leads imply a right coronary or circumflex lesion; I and aVL imply a left main stem or LAD lesion.

Competing interests: None declared

Philip Pearson, Clinical Research Fellow

Division of Respiratory Medicine, City Hospital, Nottingham, NG5 1PB.

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The easiest way to decide axis is to remember the leads in the vertical plane. The tallest R wave in the limb leads roughly implies the direction of the net vector of the cardiac impulse. Thus, the axis can be remembered as follows:

A tall R wave in

Lead I- Horizontal heart
Lead II- Normal axis
Lead III-Right axis deviation
AVR- Grossly abnormal axis
AVL- Left axis deviation
AVF- Vertival heart

Competing interests: None declared

A.B. GOPALAMURUGAN, SHO-CARDIOLOGY

KINGSMILL HOSPITAL, SUTTON IN ASHFIELD-NG17 4NZ

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16 February 2002

I can mention a most simplest method than Meek and Morris's for calculating the cardiac axis.In this method let's consider our left hand as DI and right hand as aVF. If both DI and aVF are positive we should raise both hands and this means normal axis. If DI is positive and aVF is negative we should raise our left hand and this means that left axis.

Finally, we can say right axis deviation if our right hand raised alone for positive aVF derivation.

I think this is most practical method for beginners.

Competing interests: None declared

Serdar KULA, Pediatrician, Fellow in Pediatric Cardiology

Gazi University Medical School Department of Pediatric Cardiology, 06500 Besevler ANKARA, TURKEY

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An article on basics of electrocardiography emphasizes the fact that electrocardiogram is indispensable. We beg to differ that the method stated is not the simplest method to calculate the axis. Instead of analysing all the three leads, assessment of leads I and avF are sufficient. If both are predominantly positive and negative, the axes are normal and indeterminate axes respectively. If I is predominantly negative and avF is predominantly positive, it is right axis and the vice versa is left axis. In order to differentiate physiologic and pathological left axis deviation i.e more than -30 degrees, the lead II should be predominantly negative for the latter.

Competing interests: None declared

Ramachandran Sivakumar

R.Kirthivasan,G.Jeyasangar

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