Which of the following is the classic EKG finding in atrial flutter?

The classic EKG finding in atrial flutter is the sawtooth pattern of P waves, often referred to as "F-waves." These are best visualized in the inferior leads (II, III, and aVF) and appear as a series of rapid, regular, and jagged deflections resembling the teeth of a saw. This characteristic pattern results from a reentrant circuit within the atria, usually around the tricuspid valve in the right atrium. The atrial rate in atrial flutter is typically around 240 to 340 beats per minute, and the sawtooth appearance is distinct and helps differentiate atrial flutter from other arrhythmias.

The other options do not represent classic findings associated with atrial flutter. Flat T waves typically relate to ischemia or electrolyte abnormalities, wide QRS complexes signify ventricular conduction issues or pre-excitation syndromes, and inverted U waves can indicate conditions like repolarization changes. Therefore, the presence of sawtooth P waves is the definitive classic finding indicative of atrial flutter on an electrocardiogram.