A number of patients on an acute cardiac care unit of a hospital have diagnoses of impaired cardiac conduction. Which of the following patients is most deserving of immediate medical attention?

a) A 69-year-old woman who has entered ventricular fibrillation.
b) A 60-year-old woman who has just been diagnosed with a first-degree AV block.
c) A 60-year-old man with premature ventricular contractions (PVC) and a history of atrial fibrillation.
d) A 46-year-old man whose cardiac telemetry shows him to be in ventricular tachycardia.