Final answer:
Hydrochlorothiazide, a diuretic, can cause hypokalemia, leading to heart palpitations and irregular heartbeats in the elderly male client reported in the case.
Step-by-step explanation:
The most likely cause of a 75-year-old male client experiencing "palpitations" and "skipped heart beats" after taking hydrochlorothiazide (HCTZ) is an electrolyte imbalance, specifically hypokalemia, which means low potassium levels. HCTZ is a diuretic that can increase the frequency of urination and, as a result, can lead to the depletion of potassium. The heart relies on a complex balance of electrolytes, particularly potassium, to function properly. Therefore, an imbalance such as hypokalemia can cause arrhythmias, including palpitations and irregular heartbeats. Regular monitoring of electrolytes is crucial in patients on diuretics like HCTZ to prevent these cardiac side effects.