EFFECT OF CHANGES IN ELECTROLYTE CONCENTRATION ON HEART

Distribution of electrolytes in extracellular fluid and intracellular fluid is responsible for the electrical activity of the tissues including myocardium. Thus, any change in the concentration of any electrolyte will definitely alter the electrical activity of cardiac muscle.

EFFECT OF CHANGES IN SODIUM ION CONCENTRATION

Normal sodium ion concentration in blood is 135 to 145 mEq/L. Change in concentration of sodium ion does not alter the electrical activity of heart severely. Only the low level of sodium ion in body fluids reduces the electrical activity of cardiac muscle and electrocardiogram (ECG) shows low-voltage waves.

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EFFECT OF CHANGES IN POTASSIUM ION CONCENTRATION

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

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EFFECT OF HYPERKALEMIA

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Hyperkalemia decreases:

1. Resting membrane potential, leading to hyperpolarization

2. Excitability of the muscle.

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Changes in ECG When Potassium Level Increases to 6 or 7 mEq/L

T wave is tall and tented.

?P-R interval and QRS complex are normal.

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Changes in ECG When Potassium Level Increases to 8 mEq/L

P-R interval and the duration of QRS complex are prolonged because, hyperkalemia decreases the rate of conduction.

?P wave may be small.

Changes in ECG When Potassium Level Increases beyond 9 mEq/L

Severe hyperkalemia makes the atrial muscle unexcitable. So, P wave is absent in ECG. QRS complex merges with T wave. This condition is fatal because, it leads to ventricular fibrillation or stoppage of heart in diastole, due to the lack of excitability.

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EFFECT OF HYPOKALEMIA

Hypokalemia decreases the sensitivity of heart muscle.

Changes in ECG When Potassium Level Falls to 2 mEq/L

1. S-T segment is depressed

2. T wave is small, flat or inverted

3. U wave appears. Sometimes, the U wave merges with T wave. Because of this, the Q-T interval is mistaken for being prolonged.

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Changes in ECG When Potassium Level Falls below 2 mEq/L

?1. Depression of S-T segment below the isoelectric baseline

2. Inversion of T wave

?3. Appearance of prominent U wave

4. Prolongation of P-R interval.

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EFFECT OF CHANGES IN CALCIUM ION CONCENTRATION

Normal concentration of calcium ion in blood is 9 to 11 mg/dL (4.5 to 5.5 mEq/L). Mostly, hypocalcemia affects the heart, rather than hypercalcemia.

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EFFECT OF HYPERCALCEMIA

Hypercalcemia is the elevation in blood calcium level. It increases the excitability and contractility of the heart muscle. In clinical conditions, the effect of hypercalcemia is very rare.

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Changes in ECG

1. Shortening of duration of S-T segment

2. Shortening of QT interval

3. Appearance of U wave.

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Calcium Rigor

?Stoppage of the heart in systole, due to hypercalcemia is called the calcium rigor. Calcium rigor is a reversible phenomenon and the heart starts functioning normally, when the calcium ions are washed.

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EFFECT OF HYPOCALCEMIA

?Hypocalcemia is the reduction in blood calcium level. It reduces the excitability of the cardiac muscle.

?Changes in ECG

?1. Prolongation of S-T segment

2. Prolongation of Q-T interval

3. Appearance of a prominent U wave.

Thanks and Regards,

Amita Rao

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