Final answer:
An ectopic focus or ectopic pacemaker is an area of the heart other than the SA node that initiates an impulse followed by a premature contraction. It can be stimulated by localized ischemia, exposure to certain drugs, elevated stimulation by the autonomic nervous system, or other pathological conditions.
Step-by-step explanation:
An ectopic focus or ectopic pacemaker is an area of the heart other than the SA node that initiates an impulse followed by a premature contraction. It can be stimulated by localized ischemia, exposure to certain drugs, elevated stimulation by the autonomic nervous system, or other pathological conditions. If the condition becomes chronic, it may lead to arrhythmias or fibrillation. This shows that the answer to the question is (b) Ectopic.