Final answer:
An irregular P rhythm with morphology of premature P waves that look different is often caused by an ectopic focus or ectopic pacemaker in the heart.
Step-by-step explanation:
An irregular P rhythm with morphology of premature P waves that look different is often caused by an ectopic focus or ectopic pacemaker in the heart. These ectopic foci can be stimulated by ischemia, certain drugs, or elevated stimulation by the autonomic nervous system. They can lead to arrhythmias or fibrillation if they become chronic.