Final answer:
The most specific ECG change for digoxin toxicity is the downsloping of the ST-segment, which is sometimes referred to as a 'reverse tick' or 'digoxin effect.'
Step-by-step explanation:
The most specific electrocardiogram (ECG or EKG) change for digoxin toxicity is c) Downsloping ST-segment. Digoxin toxicity can cause a variety of ECG changes. One of the characteristic findings is a downsloping of the ST-segment, often referred to as a 'reverse tick' appearance or 'digoxin effect.' This finding can sometimes be seen even at therapeutic levels of digoxin and therefore may not always indicate toxicity.
Additionally, d) Bidirectional ventricular tachycardia is a rare but potentially life-threatening arrhythmia that can also be a sign of digoxin toxicity. However, it's not as commonly seen as ST-segment changes. b) PR interval prolongation and other arrhythmias can also occur but are less specific to digoxin toxicity. To clarify common ECG components: the P wave represents atrial depolarization, the QRS complex represents ventricular depolarization, and the T wave indicates ventricular repolarization. Atrial repolarization is not visible on the ECG because it occurs during the ventricular depolarization and is masked by the larger QRS complex.