Cardiac Vessels,Muscles and Nerve Supply

  • RCA gives rise to acute marginal, right conus (infundibular), posterior interventricular /descending (in most 67-90% cases and these are k/a right dominant), and nodal artery (in 65% cases). 
  • Right coronary artery arise from anterior aortic sinus, has lesser diameter (than LCA), supplies major part of right ventricle & right atrium.
  • Left coronary artery (LCA) gives rise to Circumflex Coronary, Obtuse marginal, left diagonal, and anterior interventricular (descending) artery.
  • Right coronary artery supplies
  1. SA node (in 65%),
  2. whole conducting system (AV bundle, bundle of his, part of left bundle branch) except RBB and part of left branch of AV bundle,
  3. posterior part of ventricular septum,
  4. most of right ventricle except small part adjoining anterior interventricular groove and small part of left ventricle adjoining posterior interventricular groove.
  • Left coronary artery supplies
  1. most of the left atrium,
  2. most of the left ventricle including apex,
  3. small part of right ventricle odjoining anterior interventricular septum,
  4. anterior 2/3 of ventricular septum,
  5. RBB, LBB 
  6. SA node in 35% of cases.
  • The site of involvement of Arteries and the corresponding sites of myocardial lesions:
  • Left anterior descending artery (40-50%)
  1. Anterior wall of left ventricle near apex
  2. Ant. portion of ventricular septum
  3. Apex Circumferentially
  • Right coronary artery (30-40%)
  1. Inf post. wall of left ventricle
  2. Post. portion of ventricular septae
  3. Inf post. right ventricular free
  • Left circumflex artery (15-20%)
  • Lateral wall of left ventricle except at apex.
  • Atherosclerosis in the coronary circulation most commonly affects Left anterior descending artery.
  • Common sites of occlusion are Left anterior descending ,Right coronary artery , Circumflex coronary artery
  • Ischemia in the distribution of Left Circumflex Artery is difficult to detect on standard 12 lead ECG.
  • Coronary occlusion is caused by Atheromatous narrowing of vessel , Atheromatous narrowing of vessel , Rupture of atheromatous plaque in to the lumen.
  • Cardiac dominance is determined by coronary artery supplying circulation to the inferior portion of the interventricular septum.
  1. Cardiac dominance is based on Posterior Interventricular Artery.
  2. In 85% of patients the right coronary artery (RCA) is said to be "dominant" because it supplies circulation to the inferior portion of the interventricular septum via the right posterior descending coronary artery/posterior interventricular artery.
  3. In 'right dominance' the posterior interventricular (descending) artery is derived from right coronary artery ; in left dominance' it is a branch of circumflex, branch of left coronary artery. (15%)
  • The coronary sulcus is the groove which separates the atria from the ventricles. The right and left coronary arteries, circumflex artery, and coronary sinus all lie in this groove. 
  • The right marginal artery is a branch of the right coronary artery which lies on the right ventricle and supplies that chamber of the heart.
  • Coronary blood flow is directly related to the perfusion pressure (aortic diastolic pressure) and the duration of diastole.
  1. Coronary blood flow is inversely proportional to coronary vascular resistance..
  2. Coronary blood flow per minute is 250ml/min, which represents approximately 4% of the normal resting cardiac output.
  3. Blood supply during exercise is increased in Coronary Circulation.
  • The critical narrowing of coronary vessels to cause angina is more than 70 %.
  • Cardiac muscle consists of striated muscle fibers that branch and unite with each other. Cardiac muscle has a large central nucleus.
  • Its fibers tend to be arranged in whorls and spirals, and they have the property of spontaneous and rhythmic contraction. Specialized cardiac muscle fibers form the conducting system of the heart.
  • Cardiac muscle is supplied by autonomic nerve fibers .
  • Venous drainage of heart
  1. Coronary sinus : Opens into right atrium and has following tributries : (i) Great cardiac vein, (ii) Middle cardiac vein, (iii) Posterior vein of left ventricule, (iv) Small cardiac vein, (v) Oblique vein of left atrium and (vi) Sometimes right marginal vein.
  2. Anterior cardiac vein : Opens into right atrium.
  3. Venae cardis minimi (thebasian veins) : Open into right atrium.
  4. Right marginal vein : More often opens into right atrium but sometimes into coronary sinus.
  • Channel which drains major part of myocardium is Coronary Sinus.
  • Factors leading to vasodilatation include: 02 ,lack and increased local concentrations of CO2 ,H+, Lactate, Prostaglandins, Adenine nucleotides, and Adenosine.
  • Maximum coronary blood flow occurs during the phase of isovolumetric ventricular relaxation phase.
  • Nerve Supply of Heart:
  • Motor component
1. Superficial cardiac plexus :- Lies in front of right pulmonary artery below the arch of aorta. It is fored by:- o Superior cervical cardiac branch of the left sympathetic chain.
  • Inferior cervical cardiac branch of left vagus.
  • A small ganglion, the cardiac ganglion of Wrisberg, is occaisonally found connected with these nerves at their point of junction. This ganglion, when present, is situated immediately beneath the arch of aorta, on right side of ligamentum arteriosum.
2. Deep cardiac plexus :- Lies in fron of the bifurcation of trachea, behind the arch of aorta. It is formed by all sympathetic and parasympathetic cardiac branches except those forming the superficial plexus.
  • Sensory component
  • Pain sensation arising due to ischemia is conveyed by afferents which pass through sympathetic cardiac fibers and reach the T1 to T, cord segments on left side.
  • Grooves (sulci) of heart
A  Atrioventricular groove
  • Atria are separated by ventricles by atrioventricular Sulcus (atrioventricular groove, also called coronary sulcus).
  • It is divided into anterior and posterior parts. The right half of anterior part is large and lodges right coronary artery. Left half of anterior part is small and lodges circumflex branch of left coronary artery.
B  Interventricular grooves
  • Right and left ventricles are separated by interventricular grooves.
  • Anterior interventricular groove is nearer to left margin of heart and contains anterior interventricular artery (also called left anterior descending artery).
  • Posterior interventricular groove is situated on diaphragmatic (inferior) surface. It contains posterior interventricular artery (continuation of RCA).
  • Human Cardiac Muscle Contains both alpha and beta heavy chains of myosin.
  • Regulation of coronary flow occurs by two mechanisms : ?
1 Chemical regulation (Autoregulation)
  • Regulation of coronary blood flow occurs through local intrinsic regulation, i.e., autoregulation, most likely through the production of vasodilating metabolites in response to minimal degree of ischemia. The vasodilatory chemical stimuli are low PO2, High PCO2, H+, K+, lactic acid, ADP AMP and adenosine. Chemical regulation (autoregulation) of coronary blood flow is far more important than neural regulation.
2 Neural regulation
  • Coronary arteries are supplied by autonomic sympathetic and parasympathetic system.
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