Anatomy and Physiology of the Cardiovascular System
The heart is a four-chambered pump: right atrium → right ventricle → pulmonary artery → lungs → pulmonary veins → left atrium → left ventricle → aorta → body. The right side handles deoxygenated blood to the lungs; the left side pumps oxygenated blood systemically and is thicker-walled.
Conduction system
The SA node (sinoatrial) is the primary pacemaker in the upper right atrium, firing 60–100 times per minute. The AV node slows conduction, allowing atria to empty before ventricles contract, and serves as a backup pacemaker (40–60 bpm). The bundle of His carries impulses to the ventricles, splitting into right and left bundle branches, terminating in Purkinje fibers (20–40 bpm). This hierarchy explains why a blocked SA node may produce a slower escape rhythm.
The cardiac cycle and EKG correlation
Atrial depolarization = P wave. Ventricular depolarization = QRS complex. Ventricular repolarization = T wave. Atrial repolarization is hidden in the QRS. The PR interval reflects AV conduction; the QT interval reflects total ventricular activity.
Coronary circulation and valves
Coronary arteries supply the myocardium; the left anterior descending (LAD) feeds the anterior wall, the circumflex the lateral wall, and the right coronary artery the inferior wall and often the SA/AV nodes. Valves (tricuspid, pulmonic, mitral, aortic) prevent backflow.
Traps
Questions confuse the pacemaker hierarchy (SA fastest, Purkinje slowest) and which wave represents which event. Remember: P = atria, QRS = ventricles, T = ventricular recovery. Also know that the left ventricle is the thickest chamber and that the LAD supplies the anterior wall.
Rule of thumb: Depolarization = contraction; repolarization = recovery.