MICROANATOMY

Detailed explanation-1: -The SA node has the highest inherent rate of depolarization and therefore referred to as the pacemaker of the heart. It initiates the sinus rhythm or normal electrical pattern. This impulse spreads from the SA node to the atrial myocardial contractile cells and the AV node.

Detailed explanation-2: -The P wave indicates atrial depolarization. The P wave occurs when the sinus node, also known as the sinoatrial node, creates an action potential that depolarizes the atria. The P wave should be upright in lead II if the action potential is originating from the SA node.

Detailed explanation-3: -The conduction system of the heart. Left: Normal excitation originates in the sinoatrial (SA) node then propagates through both atria. The atrial depolarization spreads to the atrioventricular (AV) node, and passes through the bundle of His to the bundle branches/Purkinje fibers.

Detailed explanation-4: -The SA node starts the sequence by causing the atrial muscles to contract. That’s why doctors sometimes call it the anatomical pacemaker. Next, the signal travels to the AV node, through the bundle of HIS, down the bundle branches, and through the Purkinje fibers, causing the ventricles to contract.

Detailed explanation-5: -The heart’s intrinsic pacemaker, the sinoatrial node (SAN), generates spontaneous action potentials (AP) through a system of coupled oscillators whose common output initiates each normal heartbeat.