U01.07.006 Anatomy of the heart

The Left Atrium (LA) is the most posterior part of the heart. Enlargement of the LA, such as in mitral stenosis, can cause compression of the esophagus (leading to dysphagia) and/or the left recurrent laryngeal nerve, which may result in hoarseness (known as Ortner syndrome).
The Right Ventricle (RV) is the most anterior part of the heart and is the most commonly injured area in trauma.

The pericardium consists of three layers from outer to inner:

Fibrous Pericardium – the tough outer layer.
Parietal Layer of Serous Pericardium – the inner lining of the fibrous pericardium.
Visceral Layer of the Serous Pericardium – also called the epicardium, it directly covers the heart.

Pericardial Cavity: The space between the parietal and visceral layers.
Innervation: The pericardium is innervated by the phrenic nerve.
Clinical Relevance: Pericarditis can cause referred pain to the neck, arms, or shoulders (often the left).

Left Anterior Descending (LAD) Artery:
- Supplies anterior 2/3 of the interventricular septum, anterolateral papillary muscle, and anterior surface of the left ventricle (LV).
- Most commonly occluded in myocardial infarctions.
Posterior Descending Artery (PDA):
- Supplies the AV node (dependent on dominance), posterior 1/3 of the interventricular septum, posterior 2/3 of the ventricular walls, and posteromedial papillary muscle.
Right Coronary Artery (RCA):
- Supplies the SA node (independent of dominance). Infarction here may cause nodal dysfunction (bradycardia or heart block).
- The right (acute) marginal artery supplies the right ventricle (RV).

Right-Dominant Circulation (85%): The PDA arises from the RCA.
Left-Dominant Circulation (8%): The PDA arises from the left circumflex artery (LCX).
Codominant Circulation (7%): The PDA arises from both the RCA and LCX.
Coronary Blood Flow: Peaks in early diastole.

Left Atrium (LA): The most posterior part of the heart. Enlargement can lead to dysphagia and hoarseness due to compression of the esophagus and left recurrent laryngeal nerve.
Right Ventricle (RV): The most anterior part of the heart and prone to injury in trauma.
Pericardium: Composed of three layers, fibrous, parietal, and visceral, and is innervated by the phrenic nerve.
Coronary Supply:
- LAD: Supplies the anterior 2/3 of the interventricular septum.
- PDA: Dependent on dominance, supplies the posterior 1/3 of the interventricular septum and AV node.
- RCA: Supplies the SA node, and RCA infarction can lead to bradycardia or heart block.
Dominance in Coronary Circulation: Right-dominant (85%), left-dominant (8%), and codominant (7%) circulations.
Coronary blood flow peaks during early diastole.

USMLE Step 1 Review Series