Heart-arterial supply, nerve supply, veins of heart

ARTERIAL SUPPLY OF HEART

• The arterial supply of the heart is provided by the right & left coronary arteries, which arise from the ascending aorta above the aortic valve.

 CARDIAC DOMINANCE

• The artery from which the posterior interventricular artery (posterior descending artery (PDA) arises determines the coronary dominance.
• RIGHT DOMINANT HEART: In 90% cases, right coronary artery gives posterior interventricular artery.
• LEFT DOMINANT: in 10% cases, posterior interventricular artery is a branch of circumflex artery.
• In CODOMINANCE or BALANCED PATTERN, branches of both RCA & LCA run in the posterior interventricular groove.
• Dominance should not be confused with the amount of tissue supplied: left coronary artery supplies major part of heart, whether right dominance or left dominance.  

INVOLVEMENT OF CORONARY CIRCULATION IN THROMBOSIS

1. Left anterior descending artery (anterior interventricular) artery is most commonly involved in thromboticocclusion.

• This results in infarction of anterior wall of left ventricle, apex of heart & anterior 2/3 of ventricular septum.

2. Right coronary artery or its posterior interventricular branch is involved 2nd most commonly.

• This results in infarction of inferior/posterior wall of left & right ventricle, posterior 1/3 of ventricular septum.

3. 3rd most commonly involved vessel is circumflex coronary artery (branch of LCA).

• This results in infarction of lateral wall of left ventricle except apex.

4. Left main coronary artery, diagonal branches of LAD artery & marginal branches of circumflex artery are uncommon to be involved.

 BLOOD SUPPLY OF CONDUCTING SYSTEM OF THE HEART: 

• SA NODE: right coronary artery (nodal branch) (65%), left coronary artery (35%).
• AV NODE, AV BUNDLE & BUNDLE OF HIS: right coronary artery.
• RIGHT BUNDLE BRANCH: left coronary artery
• LEFT BUNDLE BRANCH: mostly by left coronary artery, few parts by right coronary artery.

VEINS OF THE HEART

1. Coronary Sinus:

• Largest vein of the heart situated in the left Posterior coronary sulcus.
• Ends by opening into the posterior wall of the right atrium b/w IVC opening & AV orifice.
• Orifice of coronary sinus is guarded by thebesian valve while IVC orifice is guarded by rudimentary Eustachian valve (SVC orifice has no valve).
• Coronary sinus develops from body & left horn of sinus venosus.

The tributaries are:

1. Great cardiac.V (anterior interventricular vein)→ Enters the left end of coronary sinus at its origin,
2. Middle cardiac V (posterior interventricular vein)  → Joins the middle part of coronary sinus
3. Small cardiac vein  → Joins the right end of coronary sinus
4. Posterior vein of left Ventricle → Ends in middle of coronary sinus
5. Oblique Vein of left atrium of Marshalls → Terminates in left end of coronary sinus (Develops from left common cardinal Vein (duct of curier)

2.  Anterior Cardiac Veins:

• These veins are 3 or 4 small veins which run parallel to each other on the anterior wall of right ventricle.
• Opens directly into the right atrium through its anterior wall.

3. Thebesian Veins (Venae Cordis minimi)

• They are the numerous small veins present in all the four chambers.
• These drains into right atrium.
• The venae Cordis minimi are more numerous on right side & least in left ventricle.

NERVE SUPPLY OF HEART

Has both   i) motor  &  ii) sensory components

MOTOR COMPONENT:

• Motor component includes parasympathetic & sympathetic systems.
• Parasympathetic fibers reach the heart through vagus & are cardioinhibitory.
• Sympathetic fibers are derived from T1 to T5 segment of spinal cord & are cardiostimulatory (excitatory).
• SA node is supplied by right vagus/parasympathetic (inhibitory) and right Sympathetic (excitatory) system.
• Both parasympathetic & sympathetic nerves form the superficial & deep cardiac plexus, the branches of which run along the coronary arteries to reach the myocardium.

 → A small ganglion, the cardiac ganglion of Wrisberg, is occasionally found connected with these nerves at their point of junction.

→ This ganglion , when present, is siyuated immediately beneath the arch of aorta, on right side of ligamentum arteriosum. 

SENSORY COMPONENT:

• Pain sensation arising due to ischemia is conveyed by afferents which pass through sympathetic cardiac fibers & reach the T1 to T5 cord segments on left side.
• Since these dorsal root ganglia also receives sensory impulses from the medial side of arm, forearm & upper part of front of vhest, the pain gets referred to these areas through these thoracic splanchnic nerves (T1-T4).