What is an ECG?

Electrocardiogram (EKG or ECG) is the record or graphical registration of electrical activities of the heart, which occur prior to the onset of mechanical activities. It is the summed electrical activity of all cardiac muscle fibres recorded from the surface of the body.

Electrocardiography is the technique by which these electrical activities of the heart are studied, and an electrocardiograph is an instrument or machine by which electrical activities are being recorded.

Also Check: MCQs on ECG

Concentration of Potassium Ion

The distribution of electrolytes like magnesium, sodium, potassium and calcium in extracellular and intracellular fluid is responsible for the electrical activity of most tissues, including the myocardium (cardiac muscle). Thus, any change in the concentration of any electrolyte will definitely alter the electrical activity of cardiac muscle. Also, changes in calcium and potassium concentration have significant effects on the heart compared to sodium ion concentration.

The normal potassium ion concentration in blood is about 3.5 to 5 mEq/L (milliequivalents per litre). Changes in ECG appear when the potassium level increases to 6 mEq/L (hyperkalemia) or when it decreases to 2 mEq/L (hypokalemia).

Hypokalemia in ECG

Decreased level of potassium ion concentration in the blood serum is termed hypokalemia or hypopotassemia. It typically increases the risk of arrhythmias (irregular heartbeat) and can lead to cardiac arrest. In general, hypokalemia decreases the sensitivity of heart muscle.

Potassium concentration slightly below the normal level (<3.5 mEq/L) can be managed through dietary supplementation. If it decreases to 2 mEq/L, then intravenous replacement of potassium ion is needed. Hypokalemia can be easily diagnosed through a blood test. But, ECG shows the prominent changes that occur during hypokalemia.

Effect of Hypokalemia on ECG

As mentioned before, hypokalemia leads to prominent ECG changes. It has a decreasing effect on the sensitivity of the heart muscles. Thus the following changes can be observed in the ECG in the case of hypokalemia –

Changes in ECG when potassium level falls to 2 mEq/L

The S-T segment is depressed
The T wave is flat, small or inverted
Sometimes, an additional U wave appears and merges with the T wave
This gives an illusion of a prolonged Q-T interval

Changes in ECG when potassium level falls below 2 mEq/L

Depression in the S-T segment below the isoelectric baseline
Inversion of T wave
Prolongation of P-R interval
A prominent U wave appears

Hyperkalemia vs Hypokalemia – Changes in ECG

Hyperkalemia is the elevated potassium ion concentration in blood. It results in decreased resting membrane potential of heart muscles leading to hyperpolarisation. Also, it decreases the excitability of the muscles.

Changes in ECG during Hyperkalemia	Changes in ECG during Hypokalemia
Tall and tented T wave	Flat, small or inverted T wave
Prolonged P-R interval and wide QRS complex. Under severe conditions, the P wave is very small or absent	The S-T segment is depressed and the depression is found below the isoelectric baseline
During extreme hyperkalemia, the QRS complex merges with the T wave and denotes a fatal condition	Sometimes, the U wave appears and merges with the T wave. During extreme hypokalemia, the U wave is prominent

Frequently Asked Questions

What is the significance of an ECG?

An electrocardiogram (ECG) is useful in determining and diagnosing the heart rate, heart rhythm, coronary artery disease, heart attack, poor blood flow to the heart muscles and abnormal electrical conduction.

What is hyperkalemia?

If the potassium ion concentration increases above 5.5 or 6 mEq/L in the blood serum, it is termed hyperkalemia. Hyperkalemia typically affects the excitability of the heart muscles and can also lead to cardiac arrest.

What is the difference between hypokalemia and hyperkalemia in ECG?

Hypokalemia is decreased potassium concentration, and hyperkalemia is increased concentration. In ECG, hypokalemia is represented by a fat, small or inverted T wave. Whereas, hyperkalemia is characterised by a tall and tented T wave.

What happens during a change in calcium ion concentration?

Calcium is also a vital electrolyte that has an effect on cardiac functioning. The normal concentration of calcium ion in the blood is 4.5 to 5.5 mEq/L. Here, hypocalcemia (decrease in calcium) affects the heart rather than hypercalcemia (increase in calcium).

Explore: NEET MCQs on Human Heart

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