Internal Anatomy: Chambers, Valves, and the Cardiac Skeleton

Overview: Why Internal Anatomy Matters for EKG Technicians

An EKG records the electrical events that make the heart pump. To interpret those recordings safely and accurately, you must first understand the physical structures the electricity controls. This lesson takes you inside the heart to trace the path blood follows through all four chambers and across each of the four valves.

The Four Chambers

The heart is divided into a right side and a left side by a muscular wall called the interventricular septum (between the ventricles) and the interatrial septum (between the atria). Each side has two chambers: an upper atrium that receives blood and a lower ventricle that pumps blood out.

• Right atrium (RA): Receives oxygen-poor blood from the body through the superior and inferior venae cavae and from the heart muscle itself through the coronary sinus.
• Right ventricle (RV): Receives blood from the RA and pumps it to the lungs through the pulmonary trunk.
• Left atrium (LA): Receives oxygen-rich blood returning from the lungs through four pulmonary veins.
• Left ventricle (LV): Receives blood from the LA and pumps it to the entire body through the aorta. The LV wall is significantly thicker than the RV wall because it must generate much higher pressure.

Tracing Blood Flow Step by Step

1. Oxygen-poor blood enters the right atrium from the venae cavae.

2. The RA contracts, pushing blood through the tricuspid valve into the right ventricle.

3. The RV contracts, pushing blood through the pulmonary valve into the pulmonary arteries toward the lungs.

4. In the lungs, blood drops off carbon dioxide and picks up oxygen.

5. Oxygen-rich blood returns through the pulmonary veins to the left atrium.

6. The LA contracts, pushing blood through the mitral valve (bicuspid valve) into the left ventricle.

7. The LV contracts forcefully, pushing blood through the aortic valve into the aorta and out to the body.

Remember this sequence: right atrium → tricuspid → right ventricle → pulmonary valve → lungs → left atrium → mitral → left ventricle → aortic valve → body.

The Four Cardiac Valves

Valves keep blood moving in one direction. There are two types: atrioventricular (AV) valves between atria and ventricles, and semilunar valves at the exits of the ventricles.

Atrioventricular valves:

• Tricuspid valve — located between the right atrium and right ventricle; has three leaflets (cusps). Opens when the RA contracts; closes when the RV contracts to prevent backflow into the RA.
• Mitral valve (bicuspid valve) — located between the left atrium and left ventricle; has two leaflets. Opens when the LA contracts; closes when the LV contracts to prevent backflow into the LA.

Semilunar valves:

• Pulmonary valve — located at the base of the pulmonary trunk, between the RV and pulmonary arteries; has three half-moon-shaped cusps. Opens when the RV contracts; closes when the RV relaxes to prevent backflow.
• Aortic valve — located at the base of the aorta, between the LV and the aorta; has three half-moon-shaped cusps. Opens when the LV contracts; closes when the LV relaxes to prevent backflow.

Supporting Structures: Chordae Tendineae, Papillary Muscles, and the Cardiac Skeleton

The AV valves require additional support to prevent them from flipping backward (prolapsing) under the high pressure of ventricular contraction.

• Chordae tendineae are fibrous cords sometimes called "heart strings." They attach the free edges of the AV valve leaflets to the papillary muscles below.
• Papillary muscles are finger-like projections of myocardium inside the ventricles. When the ventricle contracts, the papillary muscles also contract, pulling the chordae tendineae taut and holding the valve leaflets closed against backflow.
• Cardiac skeleton refers to the dense fibrous connective tissue rings (annuli) that surround all four valve openings, separate the atria from the ventricles electrically, and serve as attachment points for valve leaflets and myocardial fibers. This electrical separation means the only normal pathway for an impulse to travel from atria to ventricles is through the AV node and bundle of His — a fact you will rely on when reading EKGs.

Clinical Connection: Mitral Valve Stenosis and the EKG

Mitral valve stenosis occurs when the mitral valve opening becomes narrowed, typically from scarring (often a long-term consequence of rheumatic fever). Blood cannot flow freely from the left atrium into the left ventricle. As a result:

• The LA must work harder and over time enlarges (left atrial enlargement).
• Left atrial enlargement can produce a characteristic change in the P wave on an EKG — a notched or widened P wave sometimes called "P mitrale."
• To compensate for reduced filling, the heart may increase its rate, which you may see as a faster baseline rate or rhythm changes.

Understanding these structural consequences helps you recognize why an EKG looks the way it does — and why your accurate tracings matter to the clinical team.

Safety and Scope-of-Practice Notes

• As an EKG technician, your role is to obtain a high-quality tracing and report it to the supervising clinician. You do not diagnose valve disorders. If a tracing looks abnormal, notify the appropriate clinical staff promptly and follow facility protocol.
• Handle heart models and patient diagrams with care; report any damaged model parts to the instructor so they are not mistaken for actual anatomical features during study.
• In the clinical setting, if a patient reports chest pain, shortness of breath, or dizziness while you are preparing for or performing an EKG, stop the procedure, stay with the patient, and call for clinical assistance immediately.