Heart
Heart
Anatomy of the Heart — Study Notes
General Introduction
The heart is a conical hollow muscular organ situated in the middle mediastinum.
Enclosure
It is enclosed within the pericardium.
Etymology & Terminology
- Greek name: Cardia → Adjective: cardiac.
- Latin name: Cor → Adjective: coronary.
Position & Location
- Placed obliquely behind the body of the sternum and adjoining parts of the costal cartilages.
- 1/3rd lies to the right of the median plane.
- 2/3rd lies to the left of the median plane.
Chambers
The human heart has four chambers:
Chamber Positions & Grooves
- Atria (Latin: chamber): Lie above and behind the ventricles.
- Atrioventricular groove: Separates atria from ventricles on the surface.
- Interatrial groove: Separates the atria from each other.
- Interventricular groove: Separates the ventricles from each other; subdivided into anterior and posterior parts.
The names given to the heart chambers as right and left do not fully correspond to their location in the heart.
Measurements
External Features
The heart has:
Apex
Directed downwards, forwards, and to the left.
Base (Posterior surface)
Directed backwards.
Surfaces
- Anterior / sternocostal
- Inferior
- Right pulmonary
- Left pulmonary
Borders
The surfaces are demarcated by upper, inferior, right, and left borders.
Heart has three surfaces: Anterior, inferior, and left.
Grooves or Sulci
1. Atrioventricular or Coronary Sulcus
Circular sulcus separating the atria from the ventricles.
Divided into anterior and posterior parts.
a. Anterior part
- Consists of right and left halves.
- Overlapped anteriorly by the ascending aorta and the pulmonary trunk.
- Right half: Oblique between right auricle and right ventricle; lodges right coronary artery.
- Left part: Small between left auricle and left ventricle; lodges circumflex branch of left coronary artery.
b. Posterior part
- Intervenes between the base and the diaphragmatic surface of the heart.
- Lodges coronary sinus.
2. Interatrial Groove
Faintly visible posteriorly; hidden anteriorly by the aorta and pulmonary trunk.
3. Anterior Interventricular Groove
- Nearer to the left margin of the heart.
- Runs downwards and to the left.
- Lower end separates the apex from the rest of the inferior border of the heart.
4. Posterior Interventricular Groove
- Situated on the diaphragmatic or inferior surface of the heart.
- Nearer to the right margin of this surface.
- The two interventricular grooves meet at the inferior border near the apex.
Crux of the heart is the meeting point of interatrial, atrioventricular, and posterior interventricular grooves.
Apex of the Heart
Formed entirely by the left ventricle.
Directed downwards, forwards, and to the left.
Overlapped by the anterior border of the left lung.
Situated in the left 5th intercostal space, 9 cm lateral to the midsternal line, just medial to the midclavicular line.
Clinical Anatomy of the Apex
Apex Impulse
An outer thrust of the apex of the heart during ventricular systole.
Observed in: 5th intercostal space, just medial to the midclavicular line.
Apex Beat
Can be felt at the site of the apex impulse.
Children below 2 years
Apex is situated in the left 4th intercostal space in the midclavicular line.
Dextrocardia
- Normal cardiac apex / apex beat is on the left side.
- In dextrocardia, the apex is on the right side.
- May be part of situs inversus (a condition where all thoracic and abdominal viscera are a mirror image of normal).
Base (Posterior Surface) of the Heart
Also called the posterior surface of the heart.
Formation
Formed mainly by the left atrium and by a small part of the right atrium.
Features
Openings
- Four pulmonary veins (open into the left atrium).
- Superior and inferior venae cavae (open into the right atrium).
Vertebral Level
Related to T5 to T8 vertebrae in the lying posture; descends by one vertebra in the erect posture.
Separation
Separated from the vertebral column by:
- Pericardium
- Right pulmonary veins
- Oesophagus
- Aorta
Borders of the Heart
1. Right Border
- More or less vertical.
- Formed by the right atrium.
- Extends from superior vena cava to inferior vena cava (IVC).
2. Left Border
- Oblique and curved.
- Formed mainly by the left ventricle, and partly by the left auricle.
- Separates the anterior and left surfaces of the heart.
- Extends from apex to left auricle.
3. Inferior Border
- Nearly horizontal.
- Formed mainly by the right ventricle; a small part near the apex is formed by the left ventricle.
- Extends from IVC to apex.
- Incisura apicis cordis: A small notch on the inferior border near the apex of the heart; gives passage to the anterior interventricular branch of the left coronary artery.
4. Upper Border
- Slightly oblique.
- Formed by the two atria, chiefly the left atrium.
- Anteriorly overlapped by pulmonary trunk and aorta.
Surfaces of the Heart
1. Anterior or Sternocostal Surface
Formation
Formed mainly by the right atrium and right ventricle, and partly by the left ventricle and left auricle.
Left atrium is not seen on the anterior surface as it is covered by the aorta and pulmonary trunk.
Lung Coverage
Most of the sternocostal surface is covered by the lungs; the part lying behind the cardiac notch of the left lung is uncovered.
Clinical Significance
The uncovered area is dull on percussion, referred to clinically as the area of superficial cardiac dullness.
2. Inferior or Diaphragmatic Surface
- Rests on the central tendon of the diaphragm.
- Formation: Formed in its left 2/3rd by the left ventricle, and in its right 1/3rd by the right ventricle.
- Traversed by the posterior interventricular groove.
- Directed downwards and slightly backwards.
3. Left Surface
- Formation: Formed mostly by the left ventricle, and at the upper end by the left auricle.
- Crossed in its upper part by the coronary sulcus.
4. Right Surface
- Rounded surface formed by the right atrial wall.
- Separated from the anterior surface by the sulcus terminalis.