Atrial fibrillation occurs when action potentials fire very rapidly within the pulmonary veins or atrium in a chaotic manner. The result is a very fast atrial rate — about 400 to 600 beats per ...

ECG Examples: Premature Ventricular Contraction (PVC) ECG (Example 1) ... the extra action potential causes the SA node to become refractory to generating its next scheduled beat, ...