Murmurs

• Structure of the Heart

  • 3 main layers
  • Pericardium
  • Pericardial cavity
  • Epicardium
  • Parietal pericardium
  • Myocardium
  • Endocardium
• Structure of the Heart

  • 3 conduction nodes
  • Sinoatrial (SA) node
  • Atrioventricular (AV) node
  • Bundle of His-Purkinje fiber system
• Pericardium

  • Inelastic collagen-rich fibrous connective tissue sac around the heart
  • Provides no more than a capillary width space around heart when relaxed
• Pericardium

  • Outer layer- parietal pericardium
  • Covered in parietal pleura of mediastinum i.e. touches lungs
• Pericardium

  • Middle layer- pericardial cavity
  • Space between outer and inner layer
  • Contains serous fluid to reduce friction
• Pericardium

  • Inner layer- epicardium or visceral pericardium
  • Firmly attached to outer surface of hear
• Myocardium

  • Middle layer of heart- has striated muscle that goes in 3 different directions
  • Made of myocardial cells that contain sarcoplasmic reticulum
  • Hold Ca2+ needed to propagate action potentials
• Myocardium

  • Thickest part of the heart
  • Contractions lead to functionality of the heart to pump blood
• Endocardium

  • Thin, smooth membrane which lines the inside of the chambers of the heart and forms the surface of the valves
• Endocardium

  • Provides protection to the valves and heart chambers
• Valves

  • Tricuspid
  • Between right atrium and ventricle
  • 3 leaflets
  • Pulmonary semilunar
  • Between right ventricle and pulmonary artery
  • 3 leaflets
• Valves

  • Mitral
  • Between left atrium and ventricle
  • 2 leaflets
  • Aortic semilunar
  • Between left ventricle and aorta
  • 3 leaflets
• Valves

  • Held to papillary muscles by chordae tendineae
  • Each cusp to 2 muscles and each muscle to 2 cusps
• Atria

  • Thin-walled sinuses at base of heart
  • Both side contains an auricle
  • a small conical or ear-shaped pouch that projects from each atrium of the heart
• Atria

  • Right
  • Caudal vena cava enters caudodorsal just above coronary sinus
  • Cranial vena cava enters craniodorsal at terminal crest
  • Fossa ovalis depression of where foramen of ovale was in fetal development
• Atria

  • Left
  • Receives pulmonary veins
  • craniosinistral, craniodextral, and in some species, caudal
  • Overall same structure as right
• Ventricles

  • Left and right divided by ventricular septum
• Ventricles

  • Right
  • Wrapped around right and cranial aspects of left ventricle
  • Conus arteriosus leads to pulmonary semilunar valve
  • Trabecula septomarginalis (moderator band) stretches from septum to outer wall
  • Trabeculae carneae- ridges thought to reduce blood turbulence
• Ventricles

  • Left
  • Forms most of apex of the heart
  • Much thicker wall than right at apex
• Cardiac Vessels

  • Pulmonary trunk
  • ONLY oxygen poor artery in body
  • Right pulmonary artery
  • Right cranial lobar, middle lobar, and caudal lobar branches
  • Left pulmonary artery
  • Left cranial lobar and caudal lobar branches
• Cardiac Vessels

  • Pulmonary veins- drain into left atrium
• Cardiac Vessels

  • Aorta
  • Ascending, arch, descending (thoracic and abdominal)
  • Brachiocephalic trunk and left subclavian
  • Right subclavian comes from B. trunk
• Conduction nodes

  • Sinoatrial node
  • 1st of the conduction nodes to start signal
  • Has automaticity (spontaneous signaling)
  • Lateral wall right atrium
• Conduction nodes

  • Atrioventricular node
  • 2nd of the conduction nodes
  • On atrial septum on right atrial side
• Conduction nodes

  • Bundle of His-Purkinje fiber system
  • Last of the conduction nodes
  • Node aspect in ventricular septum and fibers extend into apex of heart
• Mitral Valve Insufficiency

  • Myxomatous growths develop on the leaflets of the mitral valve
  • Causes thickening and retraction of leaflets, leaving a small space between atrium and ventricle
  • Sometimes chordae tendineae tear and leaflet loses structure
• Mitral Valve Insufficiency

  • Blood backflows from ventricle to atrium due to pressure gradient
  • Atrium expands to accommodate new volume
  • Eventually can no longer expand and additional fluid drains back into lungs
• Mitral Valve Insufficiency Risk factors

  • ~10% of small breed dogs will develop disease
  • Average age of presentation is 8yrs
  • More often in males than females
• Mitral Valve Insufficiency Clinical signs

  • A lot of times, no clinical signs present
  • It’s found incidentally during a wellness check
• Mitral Valve Insufficiency Clinical signs

  • Progression of disease can lead to clinical signs (we will discuss once we talk about congestive heart failure)
• Dilated Cardiomyopathy

  • Ventricular muscles, predominantly the left side, weakens
  • No longer can contract appropriate and ventricle becomes wider
• Dilated Cardiomyopathy

  • This sets off renin- angiotensin- aldosterone system
  • Poor blood pressure due to lack of ability to push blood into aorta
  • Kidneys work to correct blood pressure
  • Enlarges ventricles to compensate for insufficient ability to pump
• Dilated Cardiomyopathy

  • Eventually pressure gets too high and back flows into lungs (similar to mitral valve insufficiency)
  • Right-sided almost always happens with left and not by itself
• Arrhythmogenic Right Ventricular Cardiomyopathy

  • Condition found in Boxers specifically
  • 90% in U.S. have ventricular arrhythmias but normal functioning hearts
• Arrhythmogenic Right Ventricular Cardiomyopathy

  • Can cause fainting spells and sudden death
  • Fainting happens due to significant tachycardia- can be up to 400bpm
  • Sudden death happens because they end up in ventricular fibrillation
• Arrhythmogenic Right Ventricular Cardiomyopathy

  • 10% of these dogs will also develop DCM
• Arrhythmogenic Right Ventricular Cardiomyopathy- Risk Factors

  • Diet lacking taurine
  • Suspected that legumes in grain-free diets were taurine absorption inhibitors leading to DCM
• Arrhythmogenic Right Ventricular Cardiomyopathy- Risk Factors

  • Usually presents between 3 and 7 years of age
  • Males more likely than females
  • DCM IN CATS!
  • No age, breed, or sex predisposition, but on average is seen in cats around age 10 years
• Hypertrophic Cardiomyopathy

  • Similar disease process as DCM
  • However, involves abnormal thickening of the ventricles
  • Also usually left ventricle
• Hypertrophic Cardiomyopathy

  • Alters how contractility and relaxation of the heart as it pumps blood occurs
  • If muscle is too thick, loses lumen space for blood and therefore can’t pump as much
  • Also if it’s thicker, it’s ability to have proper force of pumping is diminished
  • Leads to similar blood pressure issues