Electrical Axis Of Heart

ELECTRICAL AXIS OF HEART BY

Rear_avis

ELECTRICAL AXIS OF HEART 

Action potential is the movement of ions so it is also called as electrical current. This current after origin in SA Node travels in all directions in atria and ventricles.

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If we represent movement of current in each direction by an arrow it will be called as vector. Head of the arrow will point towards direction of current and its length will point the magnitude of current.

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Mean vector of all these vectors is called AXIS of heart. As left ventricle has largest mass and performs maximum function of heart the net current moves in the direction of left ventricle i.e downwards and to the left. So normal axis of heart is downwards and to the left.

CURRENT MOVES IN ALL DIRECTIONS BUT NET CURRENT MOVES DOWNWARD AND TO LEFT TOWARDS APEX OF LEFT VENTRICLE

BIPOLAR LIMB LEADS

UNIPOLAR LEADS

_

_

_

+ +

_

+

_

_

+ +

+

NORMAL AXIS

AXIS DEVIATION

CAUSES OF AXIS DEVIATION LEFT AXIS DEVIATION

RIGHT AXIS DEVIATION

EXTREME AXIS OR NORTH WEST AXIS DEVIATION

1.HTN 2. LVH 3. LBBB 4. LAH 5. INFERIOR M.I

1. RVH 2. RBBB 3. LPH 4. ANTERIOR M.I 5. PULMONARY EMBOLISM 6. CHRONIC LUNG DISEASES 7.DEXTROCARDIA

1.VENTRICULAR TACHYCARDIA 2. HYPERKALEMIA 3. LEAD TRANSPOSITION 4. ARTIFICIAL PACE MAKER

Determining the Axis

Predominantly Positive

Predominantly Negative

Equiphasic

EQUIPHASIC APPROACH STEP 1.  Determine which lead among 6 limb leads is equi phasic ( equal QRS portion above and below baseline) STEP 2  Move to the lead which is perpendicular to this lead LEADS I & AVF are perpendicular to each other LEADS II & AVL are perpendicular to each other LEADS III & AVR are perpendicular to each other STEP 3.  Note the QRS complex is predominantly upwards or downwards in this lead STEP 4  If QRS complex is predominantly upward, Axis is on the positive terminal of this lead.  If QRS complex is predominantly downwards Axis is on the negative terminal of this lead. NOTE: If no lead is equi phasic then find the lead with lowest voltage of QRS complex and consider it as equiphasic

EXAMPLE

1. LEAD AVF IS EQUI PHASIC 2. AVF IS PERPENDICULAR TO LEAD I SO AXIS IS SITUATED ON LEAD I 3. NOW NOTE THAT LEAD I IS PREDOMONANTLY UPWARDS SO AXIS IS ON POSITIVE TERMINAL OF LEAD I 4. POSITIVE TERMINAL OF LEAD I IS AT 0 DEGREE SO AXIS OF THIS ECG IS ZERO DEGREE WHICH IS NORMAL

Q. DETERMINE AXIS BY EQUI PHASIC APPROACH

THUMB METHOD TO DETECT ELECTRICAL AXIS 

Place your left thumb over lead I &Right thumb over lead AVF.

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Point the thumb upwards if QRS complex in the respective lead is predominantly upward and Point the thumb downwards if QRS complex in the respective lead is predominantly downwards

BOTH THUMBS UP

= NORMAL AXIS

LEFT UP

= LAD

LEFT DOWN

RIGHT DOWN RIGHT UP

BOTH THUMS DOWN

= RAD = INDETERMINATE AXIS/ NORTH WEST AXIS/ NO MANS LAND AREA

NORMAL AXIS (LEAD I & AVF BOTH UPWARDS --- BOTH THUMBS UP)

LAD (LEAD I UP & AVF DOWN --- LEFT THUMB UP, RIGHT DOWN)

RAD ( LEAD I IS DOWN & AVF IS UP– LEFT THUMB UP, RIGHT DOWN

INDETERMINATE AXIS ( BOTH LEADS --- DOWN BOTH THUMBS DOWN)

Q. DETERMINE THE AXIS BY THUMB METHOD

THANK YOU