As a medical professional with expertise in cardiology, I can tell you that the heart rhythm that typically has no P wave is known as Ventricular Fibrillation (VF). This is a life-threatening emergency where the heart quivers instead of pumping blood effectively, and it requires immediate medical attention. In the context you provided, the mention of "retrograde P waves" and "junctional rhythm" suggests that the atria are not initiating the electrical impulse for the heartbeat. Retrograde P waves are seen when the electrical impulse originates below the atria, such as in a junctional rhythm or ventricular rhythm, and these impulses travel backward towards the atria, causing the P waves to be inverted or absent. However, the specific rhythm that has no P wave at all is ventricular fibrillation. In this condition, there is no organized electrical activity in the ventricles, and thus no P waves are present on an ECG. read more >>

No atrial activity is apparent. Note the retrograde P waves that precede each QRS complex. Accelerated junctional rhythm is present in this patient. Note the inverted P waves that precede each QRS complex, with a rate of 115 bpm.read more >>