The Heart

• The heart, located in the mediastinum between the second rib and the fifth intercostal space, is two-thirds to the left of the midsternal line and anterior to the vertebral column, posterior to the sternum.
• The heart is enclosed in a double-walled sac known as the pericardium, which is covered by an epithelial membrane called serosa.
• The pericardium has two layers: the visceral layer and the parietal layer.
• The pericardial cavity is filled with fluid for lubrication to reduce friction.
• The heart consists of three layers: the epicardium, the myocardium, and the endocardium.
• The epicardium is the visceral layer of the serous pericardium.
• Left heart failure can lead to pulmonary edema.
• Right heart failure can lead to ankle and leg edema.
• Heart Attack, also known as MI, is a condition where heart cells start dying due to ischemia of the myocardium.
• STEMI, or Severe Ischemia, is usually caused by major blockage and causes extensive heart damage.
• Heart Attack shows elevation of the S-T segment on ECG.
• Non-STEMI, or Non-Severe Ischemia, is caused by partial obstruction and causes less extensive damage.
• Congestive Heart Failure is a condition where the heart is unable to pump blood as fast as it is returning.

  -left heart failure = pulmonary edema

  -right heat failure = ankle and leg edema
• The myocardium contains spiral bundles of cardiac muscle and a fibrous skeleton of the heart, made of a criss-crossing, interlacing layer of connective tissue.
• The endocardium covers the inside of the heart walls and is continuous with the endothelial lining of blood vessels.
• The atria are receiving chambers, with the right atrium receiving blood from the superior vena cava, inferior vena cava, and coronary sinus, and the left atrium receiving blood from the pulmonary vein.
• The ventricles are pumping/discharging chambers, with two types of muscles: trabeculae carneae and papillary muscles.
• The atrioventricular valves are tricuspid and bicuspid, preventing backflow of blood into the atria from ventricles, and each valve contains cusps.

  
  

  Semilunar Valves

  -Aortic and Pulmonic

  -Prevent backflow into ventricles when the ventricles relax
• 4 Chambers

  • 2 Atria
  • 2 Ventricles
• The atrioventricular groove, also known as the coronary sulcus, is located on the anterior and posterior sides of the heart.
• The right side of the heart is part of the pulmonary circuit, with a short, lower pressure circulation, while the left side is part of the systemic circuit, with a longer circulation and higher pressure.
• The coronary circulation is a smaller system that supplies the heart itself, with major arteries including the coronary, marginal, circumflex, and interventricular, and major veins including small cardiac, anterior cardiac, great cardiac, and coronary sinus.
• The heart muscle is a functional syncytium, with all muscle fibers working as one big cell due to gap junctions between the muscles, allowing the action potentials to conduct from one muscle fiber to the others.

  -regular striations- skeletal muscle

  -short, with gap junctions- smooth muscle
• The heart muscle has unique characteristics, including being branched to create a 3D network and anchored to each other by desmosomes, with intercalated discs formed, which prevent separation during contraction.
• The heart muscle has many more mitochondria than skeletal muscle, with one connective layer, three ion channels for Ca++, Na+, and K+.
• The S-T Segment in an electrocardiogram is the time ventricle fibers are depolarized.
• The Intrinsic Conduction System in cardiac muscle includes autorhythmic cells (noncontractile cells) with an unstable resting potential due to Na+ channels never closing.
• Repolarization in cardiac muscle action potential is due to inactivation of the Ca++ channels and opening of K+ channels, and is not dependent on Na+ channels.
• An electrocardiogram (ECG or EKG) is created by electrical currents produced with ion flow during depolarization and repolarization of both atria and ventricles.
• The Cardiac Conduction System includes the Sinoatrial Node (pacemaker) which creates sinus rhythm on its own 90-95 AP/min, the AV Node which slows down transmissions to 0.1 sec, and the AV Bundle/Bundle of His which splits into right and left bundle branches. Purkinje Fibers goes into myocardium (of ventricles)
• Prolonged depolarization in cardiac muscle action potential leads to a longer absolute refractory period.
• Cardiac Centers include the Cardioacceleratory Center (Sympathetic) and the Cardioinhibitory Center (Parasympathetic), both of which inhibit the SA and AV node by the vagus nerve.
• Systole in the Cardiac Cycle is when the myocardium contracts to increase pressure, closing the AV valves.
• The Ca++ in the cell binds to troponin, causing the myosin binding site to open.
• The Q-T Segment in an electrocardiogram is the time from ventricular depolarization to ventricular repolarization, which may be lengthened with damage.
• Cardiac muscle contractions can be both rhythmic and spontaneous.
• The P-Q Interval in an electrocardiogram is the time for action potential to get from atria to ventricle.
• Ventricular Filling in the Cardiac Cycle occurs mid to late diastole when AV valves are open and SL valves are closed, with 80% filling passively and the remaining 20% coming from atrial contraction.

  -End Diastolic Volume- volume in ventricle at the end of the filing cycle
• Isovolumetric Contraction in the Cardiac Cycle occurs after AV valves have closed and while semilunar valves remain closed as pressure starts to build.
• Heart sounds include two sounds (lub-dub) associated with turbulent flow after valves close, and heart murmurs which are abnormal heart sounds most often indicative of valve problems.