ECG in various Drug and Electrolyte Effects

Digitalis Effect

ECG in digitalis is manifested as:-

  • Straight downwards slope with a sharp terminal rise like mirror image of a check or correction mark. This does not coonote toxicity and is seen in digitalis therapeutic doses. However, if the beginning of ST segment with the inverse check mark configuration is already depressed below the isoelectric level, it may then be an expression of digitalis toxicity.
  • T wave amplitude is diminished in therapeutic doses of digitalis however, T wave becomes inverted when digitalis toxicity sets in.
  • QT interval shortens as digitalis accelerates the recovery of the ventricular subendocardium.
  • Paroxysmal atrial tachycardia (PAT) is the most common arrhythmia associated with digitalis toxicity.

Quinidine Effect

Quinidine is a class I antiarrhythmic drug and a cardiac depressant. It is used in the treatment of ectopic rhythms such as ventricular premature complexes, ventricular tachycardia, atrial flutter and atrial fibrillation.

ECG manifestations of Quinidine efect:-

  • QT prolongation
  • QRS widening
  • Occasionally ST segment is depressed
  • T wave may become widened, notched, flattened or inverted
  • The U wave may become slightly more prominent


ECG manifestations of Hyperkalemia:-

  • Progressive diminution and eventual disappaerance of P wave.
  • Widening of the QRS complex.
  • A bizzare intraventricular conduction disturbance.
  • Tall, widened and characteristic T wave.
  • Virtual disappearance of ST segment.


ECG manifestations of Hypokalemia are:-

  • Progressive diminution and eventual disappearance of T wave.
  • Progressive increase in the amplitude of the U wave.
  • First and second degree AV block.
  • Depression of the ST segment.


ECG manifestations of hypermagnesemia are similar to those of hyperkalemia:-

  • QRS complex may be widened.
  • PR interval is prolonged.

No definitive criteria has yet been established to differentiate between the two conditions.


ECG manifestations of hypomagnesemia are similar to those of hypokalemia:-

  • T wave becomes attenuated.
  • U wave increases in magnitude.
  • ST segment depression may occur.
  • PR interval may also be prolonged.

No definitive criteria has yet been established to differentiate between the two conditions.


ECG manifestations of Hypocalcemia:-

  • Hypocalcemia is the only condition which prolongs the QT interval only by stretching the ST segment and without affecting the T wave
  • T wave however may become symmetrical.


ECG manifestations of hypercalcemia:-

  • Marked shortening of the QT interval. The shortening is inversely proportional to the serum calcium levels.
  • The ST segment shortens so much that it virtually is incorporated into the T wave.
  • T wave becomes widened and proximal limb of T wave now becomes steeper than the distal limb i.e, reverse of the normal.

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