<prompt> The earliest sign of Hyperkalemia in ECG isFlat inverted TTall T waveLarge P-waveProlonged Q-T interval  <response>: B Tall T wave Harrison17 - 284; Harrison18 - 357; Harrison16 - 2621 Most serious effect of HYPERKALEMIA is cardiac toxicity, which does not correlate well with the plasma K concentration. The earliest electrocardiographic changes include increased T-wave amplitude, or peaked T waves. More severe degrees of hyperkalemia result in a prolonged PR interval and QRS duration, Progressive widening of the atrioventricular conduction delay, and loss of P waves. QRS complex and merging with the T wave produces a sine wave pattern. The terminal event is usually ventricular fibrillation or asystole. 