In which of these conditions can widen QRS and Tall-tented T waves be observed?

The correct option is Hyperkalemia.

Hyperkalemia is an electrolyte abnormality characterized by elevated potassium levels in the blood. Potassium plays a crucial role in maintaining the resting membrane potential of cardiac myocytes. When extracellular potassium concentration rises, it affects the electrical activity of the heart, leading to characteristic electrocardiogram (ECG) changes.

The progressive effects of hyperkalemia on the ECG can be understood through the following physiological steps:

1. Tall-Tented T Waves: As potassium levels begin to rise (typically to 5.5 - 6.5 mEq/L), repolarization of the cardiac cell membrane is accelerated. This rapid phase 3 repolarization manifests on the ECG as narrow, symmetric, and tall-tented T waves, which are most prominent in the precordial leads (V2 to V4).
2. PR Interval Prolongation and P Wave Flattening: As potassium levels continue to rise (typically 6.5 - 7.0 mEq/L), atrial conduction is depressed, leading to prolongation of the PR interval and a decrease in the amplitude of the P wave (eventually leading to the disappearance of the P wave).
3. QRS Widening: At even higher levels of potassium (typically >7.0 mEq/L), the depolarization of the ventricles is slowed. This delay in intraventricular conduction results in a progressive widening of the QRS complex.
4. Sine Wave and Ventricular Fibrillation: Ultimately, the widened QRS complex merges with the T wave, forming a classic sine wave pattern. If left untreated, this can rapidly degenerate into ventricular fibrillation or asystole.

Therefore, both widened QRS complexes and tall-tented T waves are classic ECG findings associated with Hyperkalemia.