Anatomy of the Heart: Structural, Functional, and Clinical Details

Definition: The heart is defined as a hollow muscular, somewhat conical central pumping organ.
Viscera Description: When describing the viscera of the heart, it must be noted that it includes the heart with the pericardium and the great vessels.

Apex: The apex is directed downwards, forwards, and to the left.
Base: The base is directed upwards, backwards, and to the right.
Sternocostal Surface: This surface is directed forwards and upwards.
Diaphragmatic Surface: This surface is directed downwards and somewhat backwards.

Length (Apex to Base): $12\,\text{cm}$
Antero-posterior Diameter: $6\,\text{cm}$
Greatest Transverse Diameter (Radiograph): $8-9\,\text{cm}$
Cardiothoracic Ratio Rule: On a radiograph, the greatest transverse diameter (or widest transverse diameter) should not be more than $50\%$ of the diameter of the thorax.
- If the ratio is $50\%$ or less: It is considered normal.
- If the ratio is more than $50\%$ : It is considered abnormal and indicates Cardiomegaly.

Presenting Parts:
- Apex
- Base
- 3 Surfaces: Sternocostal surface, Diaphragmatic surface, and Left surface.
- 3 Borders: Right border, Inferior border, and Left border.
Chambers of the Heart:
- Right and Left Ventricles.
- Right and Left Atria.

Interventricular Septum: This septum separates the two ventricles.
Interatrial Septum: This septum separates the two atria.
Atrioventricular Groove (Coronary Sulcus): This groove separates the atria from the ventricles on the surface of the heart.
Anterior Interventricular Groove:
- Indicates the anterior attachment of the interventricular septum.
- Contents (OSPE focus):
  1. Anterior interventricular branch of the left coronary artery.
  2. Great cardiac vein.
  3. Some amount of fat.
Posterior Interventricular Groove:
- Contents:
  1. Posterior interventricular branch of the right coronary artery.
  2. Middle cardiac vein.
  3. Some amount of fat.

Shape and Continuity: It is a 'C' shaped curve. It is deficient anteriorly due to the presence of the root of the pulmonary trunk.
Parts: It consists of an anterior part and a posterior part.
- Anterior Part: This part is further divisible into right and left portions.
Contents of the Right Portion of Coronary Sulcus:
1. Trunk of the right coronary artery.
Contents of the Left Portion of Coronary Sulcus:
1. Trunk of the left coronary artery.
2. Circumflex branch of the left coronary artery.
3. Termination of the great cardiac vein.
4. Commencement of the coronary sinus.

Origin: Both the right and left coronary arteries are branches of the Ascending Aorta.
Aortic Sinuses: At the beginning of the ascending aorta, there are dilatations called aortic sinuses.
- Right Coronary Artery: Arises from the Anterior Aortic Sinus.
- Left Coronary Artery: Arises from the Left Posterior Aortic Sinus.
Arterial Type: Coronary arteries are classified as Functional End Arteries.
- End Artery Types:
  1. True End Artery: An artery that has no pre-capillary anastomosis (e.g., the Central Artery of the Retina).
  2. Functional End Artery: An artery that possesses anastomoses, but when one major branch is blocked, the anastomosis is not sufficient to provide the necessary nutrition to the tissue.

Contents of the Posterior Part of the Atrioventricular Groove:
1. Coronary sinus.
2. Anastomosis between the right and left coronary arteries.
Crux of the Heart: This is the meeting point of the following:
1. Interatrial groove.
2. Posterior interventricular groove.
3. Posterior part of the atrioventricular groove.

Right Border:
- Extends from the opening of the superior vena cava to the inferior vena cava.
- Formed only by the right atrium.
- Separates the sternocostal surface from the base of the heart.
- Accompanied by a vertical groove called the Sulcus Terminalis, which indicates the internal Crista Terminalis.
Inferior Border:
- Extends from the opening of the inferior vena cava to the apex of the heart.
- Near the apex, it presents a notch called the Incisura Apicis Cordis.
- At this notch, the anterior interventricular branch of the left coronary artery and the posterior interventricular branch of the right coronary artery anastomose.
- Accompanied by the Right Marginal Vessels (Right marginal artery and vein).
Left Border:
- Extends from the left auricle to the apex of the heart.
- Formed mainly by the left ventricle.
- Accompanied by the Left Marginal Vessels (Left marginal artery, a branch of the left coronary artery, and the left marginal vein).

Sternocostal Surface:
- Atrial Portion: Formed by the anterior surface of the right atrium, the right auricle, and a portion of the left auricle.
- Ventricular Portion: Formed $2/3$ by the right ventricle and $1/3$ by the left ventricle.
Diaphragmatic Surface:
- Formed only by the ventricles: $2/3$ by the left ventricle and $1/3$ by the right ventricle.

Formation and Location: Formed only by the left ventricle. It is normally situated in the 5th left intercostal space, just medial to the mid-clavicular line.
Congenital Anomalies:
- Dextrocardia: A condition where the heart is situated in the 5th right intercostal space.
- Situs Inversus: When dextrocardia occurs, the sides of all viscera may change (left-side organs move to the right and vice versa).

Shape and Formation: Quadrilateral in shape. Formed only by the Atria (specifically the Left Atrium and a small portion, $1/3$ , of the Right Atrium).
Boundaries of the Base:
- Above: Bifurcation of the pulmonary trunk.
- Below: Posterior part of the atrioventricular groove.
- Right Side: Right border of the heart (at the opening of the superior and inferior vena cava).
- Left Side: Left border of the left atrium, extending from the superior pulmonary vein to the inferior pulmonary vein.
Venous Openings at the Base: Superior Vena Cava (SVC), Inferior Vena Cava (IVC), 4 Pulmonary Veins, and the Coronary Sinus.
Oblique Pericardial Sinus: The posterior surface of the left atrium forms the anterior boundary of the oblique pericardial sinus.
Vertebral Levels of the Base:
- Recumbent/Supine Position: $T5 - T8$
- Erect/Standing Position: $T6 - T9$

Intervening Structures: Between the base of the heart and the vertebral column, several structures intervene:
1. Oblique sinus.
2. Fibrous pericardium.
3. Descending aorta.
4. Right pair of pulmonary veins.
5. Esophagus with the sympathetic plexus of nerves.
6. Thoracic duct.
7. Azygos and hemiazygos veins.
8. Greater and lesser splanchnic nerves.
9. Posterior mediastinal lymph nodes.
Clinical Implications (Mitral Stenosis):
- Usually, the presence of the oblique sinus allows space for the left atrium.
- However, in mitral stenosis, the left atrium becomes distended.
- This distension can compress the esophagus, leading to difficulty in swallowing (Dysphagia).
- This clinical condition is known as Ortner's Syndrome.