What condition is most likely responsible for palpitations in a 60-year-old man who drinks 8 cups of coffee daily?

Palpitations in a patient who consumes a significant amount of caffeine, such as eight cups of coffee daily, are often associated with increased stimulation of the heart. Caffeine is a known stimulant that can lead to heightened sympathetic activity and result in premature beats.

Supraventricular premature beats (often referred to as premature atrial contractions or PACs) are common occurrences in individuals, especially in those who use stimulants. These beats originate from the atria and can create a sensation of palpitations. In this particular scenario, the high intake of caffeine is a likely trigger for these premature beats, explaining the palpitations experienced by the patient.

In contrast, conditions like second-degree atrioventricular block and sinoatrial exit block typically present with bradycardia rather than palpitations due to impaired conduction within the heart's electrical system. Ventricular tachycardia involves rapid heart rhythms originating from the ventricles and is generally associated with more severe symptoms and underlying cardiac pathology. Therefore, considering the context of caffeine consumption and the typical presentation of common arrhythmias associated with such use, supraventricular premature beats are the most likely cause of palpitations in this scenario.