Pseudo P pulmonale is seen in which electrolyte abnormality?

Correct Answer: C. Hypokalaemia

Pseudo P pulmonale (also called "pseudo-P pulmonale pattern") is a characteristic ECG finding in hypokalaemia where the T wave flattening and U wave prominence create an apparent tall P wave in the right precordial leads, mimicking right atrial enlargement. The discriminating mechanism is that hypokalaemia causes repolarization abnormalities: the U wave (representing Purkinje fibre repolarization) becomes prominent and merges with or appears as a continuation of the P wave, creating the illusion of P pulmonale. This is distinct from true P pulmonale seen in chronic lung disease or pulmonary hypertension, where actual right atrial enlargement produces genuinely tall, peaked P waves. In Indian clinical practice, hypokalaemia is commonly encountered in patients on chronic diuretics (especially loop and thiazide diuretics used for hypertension and heart failure), diarrhoeal illness (a major cause in our population), and renal tubular acidosis. The ECG changes of hypokalaemia include ST depression, T wave flattening, prominent U waves, and prolonged QT interval. Recognition of pseudo P pulmonale is critical to avoid misdiagnosing a patient as having pulmonary hypertension or chronic lung disease when the actual problem is electrolyte derangement requiring urgent potassium supplementation.

Why the other options are wrong

A. Hypocalcaemia — Hypocalcaemia causes prolonged QT interval (due to lengthened ST segment) and may produce peaked T waves, but does not produce the characteristic U wave prominence and T wave flattening that create pseudo P pulmonale. The ECG pattern in hypocalcaemia is distinctly different and relates to altered ventricular repolarization, not the atrial-mimicking pattern seen in hypokalaemia. B. Hyponatremia — Hyponatremia primarily causes neurological manifestations (seizures, altered mental status) rather than specific ECG changes. While severe hyponatremia may cause nonspecific ST-T changes and arrhythmias, it does not produce the characteristic U wave prominence and pseudo P pulmonale pattern. The ECG findings in hyponatremia are variable and not pathognomonic. D. Hypercalcemia — Hypercalcemia causes shortened QT interval (due to shortened ST segment), peaked T waves, and increased digitalis sensitivity, but does NOT produce U wave prominence or the flattened T waves characteristic of hypokalaemia. The ECG pattern in hypercalcemia is opposite to that seen in hypokalaemia and does not mimic P pulmonale.

High-Yield Facts

Mnemonics

U-PSEUDO (Hypokalaemia ECG memory) U wave prominence → Pseudo P pulmonale; T wave flattening → ST depression → QT prolongation. When you see U waves, think hypokalaemia, not lung disease. ELECTRO-K (Electrolyte ECG patterns) Hyperkalaemia = peaked T; Hypokalaemia = flat T + prominent U (pseudo P pulmonale); Hypercalcemia = short QT; Hypocalcemia = long QT.

NBE Trap

NBE may pair "P pulmonale" with chronic lung disease or pulmonary hypertension to trap students who confuse true P pulmonale (right atrial enlargement) with pseudo P pulmonale (a repolarization artifact of hypokalaemia). The word "pseudo" is the key discriminator.

Clinical Pearl

In Indian outpatient practice, a patient on chronic loop diuretics for heart failure presenting with palpitations and an ECG showing apparent "P pulmonale" should trigger immediate serum potassium measurement—the diagnosis is hypokalaemia-induced pseudo P pulmonale, not worsening pulmonary hypertension. Potassium supplementation, not escalation of cardiac drugs, is the answer.

_Reference: Harrison Ch. 226 (Electrolyte Disorders); KD Tripathi Ch. 12 (Cardiac Electrophysiology)_