EFFECT OF ELECTROLYTES ON CARDIAC RHYTHM

Prepared by: Ahmad Thanin

OBJECTIVES:By the end of session learners will be able to:

• Define Electrolytes.• Discuss the function of electrolytes• Describe the relationship of electrolyte with

heart• List down common electrolytes

responsible for cardiac function• Explain the effect of electrolytes on heart• Interpret the ECG features of different

electrolyte imbalances• Summarize the main key points of the

session

What are Electrolytes?

Chemically, electrolytes are substances that become ions in solution and acquire the capacity to conduct electricity. Electrolytes are present in the human body, and the balance of the electrolytes in our bodies is essential for normal function of our cells and our organs.

FUNCTIONS:

Electrolytes and Heart:

• The normal state of cardiac cell membrane polarization is dependent upon the maintenance of a normal ionic balance across the membranes

Common Electrolytes responsible for cardiac arrhythmias

• Potassium• Magnesium• Calcium

HYPERKALEMIA

Background•Potassium is vital for regulating the normal electrical activity of the heart.•Increased extracellular potassium reduces myocardial excitability, with depression of both pacemaking and conducting tissues.•Progressively worsening hyperkalemia leads to suppression of impulse generation by the SA node and reduced conduction by the AV node and His-Purkinje system, resulting in bradycardia and conduction blocks and ultimately cardiac arrest.

ECG features of Hyperkalemia:

• Rhythm: Atrial and ventricular rhythms are regular• Rate: Atrial and ventricular rates are within normal limits• P Wave: Mild-low amplitude, moderate-wide flattened,

severe-indiscernible• PR interval: Normal or prolonged; unmeasureable if P

wave cant be detected• QRS complex: Widened because ventricular

depolarization takes longer• QT interval: Shortened • ST segment: May be elevated in severe hyperkalemia • T wave: Tall, Peaked.

Peaked T waves in Hyperkalemia

Prolonged PR segment in Hyperkalemia

Broad P waves and QRS complexes

Loss of P waves

Bradycardia

HYPOKALEMIA

Background•Potassium is vital for regulating the normal electrical activity of the heart•Decreased extracellular potassium causes myocardial hyper excitability with the potential to develop re-entrant arrhythmias

ECG features of Hypokalemia:

• Rhythm: : Atrial and ventricular rhythms are regular• Rate: Atrial and ventricular rates are within normal limits• P Wave: Usually normal size and configuration • PR interval: May be prolonged • QRS complex: Within normal limits or possibly widened;

prolonged in hypokalemia• QT interval: Usually indiscernible as T wave flattens • ST segment: Depressed• T wave: Amplitude is decreased. Inverted T wave U

wave may appear.

T inversion and prominent U wave in Hypokalemia

Long QT interval in Hypokalemia

HYPOCALCEMIA

Background•Calcium is important in cardiac function; it exerts a positive inotropic effect on heart •Decreased calcium levels may cause decreased myocardial contraction.

ECG features of Hypocalcaemia:

• Rhythm: Atrial and ventricular rhythms are regular• Rate: Atrial and ventricular rates are within normal limits• P Wave: Normal size and configuration• PR interval: Within normal limits• QRS complex: Within normal limits• QT interval: Prolonged• ST segment: Prolonged • T wave: Normal size and configuration, may be flattened

Prolong QT interval in Hypocalcaemia

HYPERCALCAEMIA

Background•Calcium is important in cardiac function; it exerts a positive inotropic effect on heart •Increased calcium levels may block the conduction pathways of electrical impulse.

ECG features of Hypercalcemia:

• Rhythm: Atrial and ventricular rhythms are regular• Rate: Atrial and ventricular rates are within normal limits,

bradycardia or heart block may occur• P Wave: Normal size and configuration • PR interval: May be prolonged.• QRS complex: Within normal limits, may be prolonged • QT interval: Prolonged• ST segment: Normal• T wave: Normal size and configuration; may be

depressed.

Shortened QT interval in Hypercalcemia

HYPOMAGMESAEMIA

Background•Magnesium is required to support the heart muscle’s normal contraction-relaxation actions. •Decreased magnesium levels may cause irregular contraction of ventricles leading to arrhythmias.

ECG features of Hypomagnesaemia:

• Rhythm: Irregular ventricular rhythm • Rate: Atrial and ventricular rates may be regular• P Wave: May be normal • PR interval: Normal • QRS complex: Normal• QT interval: Normal • ST segment: Depressed• T wave: Tall T waves

Tall T waves in Hypomagnesaemia

Torsades de pointes

Depressed ST segment in Hypomagnesaemia

HYPERMAGMESAEMIA

Background•Magnesium is required to support the heart muscle’s normal contraction-relaxation actions. •Increased magnesium levels may cause delayed conduction of electrical impulse.

ECG features of Hypermagnesemia

• Rhythm: Atrial or ventricular rhythm may be regular • Rate: Atrial and ventricular rates may be regular• P Wave: May be normal • PR interval: prolonged• QRS complex: Widened• QT interval: Normal• ST segment: Normal • T wave: Normal

Prolonged PR interval in Hypermagnesemia

Wide QRS complex in Hypermagnesemia

In a nut shell

Hypocalcaemia- Prolonged ST and QT intervals

Hyperkalemia- shortened ST segment- widened T wave

Hypokalemia- ST depression- shallow, flat, inverted T wave- Prominent U wave

Hyperkalemia- Tall, peaked T waves- Flat P waves- widened QRS complex- Prolonged PR interval

Hypomagnesaemia- Tall T waves- Depressed ST segment

Hypermagnesemia- Prolonged PR interval- widened QRS complexes

Treatment:• Hyperkalemia Cocktail• Hypokalemia Potassium replacement• Hypercalcemia Magnesium• Hypocalcemia Calcium replacement• Hypermagnesemia Calcium replacement• Hypomagnesaemia Mg replacement