<s>[INST] context: Digitalis glycosides are effective in increasing myocardial contractility and in the treatment of certain atrial tachyarrhythmias. However, digoxin actually increases myocardial automaticity (increase in premature beats) and facilitates reentry (atrial tachycardias). Digoxin also slows conduction through A V nodal tissue and has central effects that can mimic vagal influence on the heart and thus may produce sinus arrest. Paroxysmal atrial tachycardia with variable block represents the classic rhythm of digitalis intoxication. Digoxin is profibrillatory, but its administration should not lead to atrial flutter. Therapeutic levels of digitalis generate characteristic ST - segment and T-wave changes in most individuals taking the drug. These changes are known as the digitalis effect and consist of ST -segment depression with flattening or inversion of the T wave. The digitalis effect is most prominent in leads with tall R waves. The digitalis effect is normal and predictable and does not require discontinuation of the- drug. [/INST] question: Which ECG findings represents a characteristic manifestation of digitalis toxicity? | options: A: ST -segment depression B: T-wave inversion C: Atrial flutter D: Atrial tachycardia with variable block | answer: D </s>