To understand cardiac dysrhythmias and the electrocardiograph, it is important to have a firm understanding of basic structure and function of the cardiovascular system.
The Cardiovascular System includes the blood vessels of the heart, the heart itself and the rest of the body.
The cardiovascular system transports nourishments, maintains regulatory functions, and the exchange of gases.
The system utilizes arteries and veins.
Arteries transport blood away from the heart while veins transport venous blood to the heart. Veins are similarly structured to arteries except they have valves and they transport blood to the heart, both veins and arteries have three layers but, arteries have a thicker muscular layer in comparison to veins.
Review the circulation of blood flow through the heart
Remember to study the heart from the standpoint of the right heart and the left heart. The heart is one organ but, it serves as a double pump utilizing a right pump and left pump. The right heart/pump pushes blood out of the heart into the lungs/pulmonary circulation and the left heart/pump pushes blood out of the heart into the body/systemic circulation.
The right side of the heart receives blood coming from the body systems. This blood has been used up by body processes and so this blood has less oxygen. This blood from body is carried within the inferior vena cava which drains the lower body and the superior vena cava which carries used blood from the head and upper body.
Incoming blood enters the right atrium (upper chamber) of the heart travels through the tricuspid valve into the right ventricle (lower chamber). The blood from this right ventricle travels through the pulmonary artery to the lungs.
In the lungs, the used blood releases carbon dioxide and hemoglobin binds to oxygen.
This new oxygen rich blood travels via the pulmonary veins into the left atrium (upper chamber) of the heart. This oxygenated blood moves through the bicuspid valve into the left ventricle. The left ventricle is thicker in its structure as it pumps blood out of the heart into the aorta (largest artery); the aorta will pump blood to all body systems.
Differentiate pulmonary versus systemic versus coronary circulation
Blood from the right heart flows from the right ventricle to the pulmonary circulation.
Blood returning to the heart from the lungs flows into the left heart and is pushed out of the left heart in to the systemic circulation. This systemic blood enters even the tiniest capillary beds.
As blood is pushed/ejected out of the left side of the heart from the left ventricle through the aorta, some of this blood flows into the coronary blood vessels which provide the coronary circulation giving blood, oxygen and nutrients to the heart itself.
Cardiac Electrical Conduction System
The cardiac electrical conduction system includes several pacemakers of the heart. The sinoatrial (SA) node innervates the atrium of the heart.
This pacemaker keeps the heart at a normal rhythm 60-100 beats per minute. The SA node then passes the impulse to the second pacemaker the atrioventricular (AV) node.
The AV node paces the heart at 40-60 beats per minute. The electrical impulse then passes from the AV node to the bundle of his where it bifurcates into the left and right bundle branches, down to the Purkinje Fibers which distribute the impulse throughout the bottom of the heart’s ventricles and paces the heart at 30-40 beats per minute.
1st Pacemaker Sino-Atrial Node 60-100 BPM
(sends impulse across the atria)
2nd Pacemaker Atrio-Ventricular Node 40-60 BPM
(sends impulse to the Bundle of HIS to the Bundle Branches)
3rd Pacemaker Purkinje Fibers 30-40 BPM
(sends impulse across bottom of the heart’s ventricles)