Final answer:
The common ECG finding in hypertrophic obstructive cardiomyopathy is Left ventricular hypertrophy, suggested by enlarged R waves and repolarization abnormalities in the ST segment and T waves.
Step-by-step explanation:
A common electrocardiographic finding in patients with hypertrophic obstructive cardiomyopathy is C. Left ventricular hypertrophy. This condition, which is a pathological enlargement of the heart, often for no known reason, can manifest on an ECG through altered Q waves and enlarged R waves that indicate an increased left ventricular mass. Additionally, the ST segment and T waves may be affected due to the strain pattern associated with hypertrophy, which often suggests a repolarization abnormality.