Electrocardiography

Electrocardiography is one of the most basic noninvasive diagnostic methods in medicine. Graphic record of the electrocardiography is called electrocardiogram (ECG, EKG). It is based on recording of electric potential generated by heart on body surface. This methode is used in diagnostic of heart disease.

Indications
ECG is indicated if there is suspicion on:
 * heat disease: heart attack, arrhythmias, conduction disturbances, myocardial ischemia;
 * metabolic disease: hypocalcemia or hypercalcemia, hypokalemia or hyperkalemia;
 * endocrine disease: diseases of the thyroid gland (hypothyroidism and hyperthyroidism).

Principle
Everything is based on heart depolarization and repolarization. These processes can be presented by vectors of electrical potentials. ECG is recording of summation of electrical potential vectors from multiple myocardial fibers, not only from cardiac conduction system. Every myocardial fiber can generate electrical potential. These electrical potentials are conducted by body fluids (which are very good conductors) to the body surface, where are recorded.

The 12 conventional ECG leads
These 12 leads are divided into two groups:
 * six extremity (limb) leads; they are recording electrical potentials transmitted into the frontal plane;
 * six chest (precordial) leads, they are recording electrical potential transmitted into horizontal plane.

There are the leads with their location and polarity :


 * {| class="wikitable"

|- ! !! limb !! colspan="4" | location of the limb || ! rowspan="4" style="background:#FFFAFA;" | bipolar extremity leads

-Einthoven's leads- ! rowspan="4" style="background:#FFFAFA;" | unipolar extremity leads
 * align="center" class="bluecell" height="50" | I || rowspan="3" colspan="1" | +  || left upper limb || rowspan="3" colspan="1" |  -  || right upper limb || rowspan="7" | Einthoven.png
 * align="center" class="bluecell" height="50" | II || left lower limb || right upper limb
 * align="center" class="bluecell" height="50" | III || left lower limb || left upper limb
 * align="center" class="bluecell" height="50" | II || left lower limb || right upper limb
 * align="center" class="bluecell" height="50" | III || left lower limb || left upper limb
 * align="center" class="bluecell" height="50" | III || left lower limb || left upper limb

-Goldberg's leads-
 * align="center" class="bluecell" height="50" | aVR|| colspan="4"| right upper limb lead
 * align="center" class="bluecell" height="50" | aVL|| colspan="4"| left upper limb lead
 * align="center" class="bluecell" height="50" | aVF|| colspan="4"| left lower limb lead
 * align="center" class="bluecell" height="50" | aVL|| colspan="4"| left upper limb lead
 * align="center" class="bluecell" height="50" | aVF|| colspan="4"| left lower limb lead
 * align="center" class="bluecell" height="50" | aVF|| colspan="4"| left lower limb lead

! rowspan="6" style="background:#FFFAFA;" | unipolar chest leads

-Wilson's leads- | align="center" class="bluecell" height="50" | V1 || colspan="4"| fourth intercostal space, just to the left of the sternum || rowspan="6" | |- | align="center" class="bluecell" height="50" | V2 || colspan="4"| fourth intercostal space, just to the left of the sternum |- | align="center" class="bluecell" height="50" | V3 || colspan="4"| midway between V2 and V4, fifth intercostal space |- | align="center" class="bluecell" height="50" | V4 || colspan="4"| fifth intercostal space, midclavicular line on the left |- | align="center" class="bluecell" height="50" | V5 || colspan="4"| fifth intercostal space, anterior axillary line |- | align="center" class="bluecell" height="50" | V6 || colspan="4"| fifth intercostal space, midaxillary line
 * }

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 * ECG abnormalities