Cardiovascular System and Heart Failure

Cardiovascular System Functions

• The heart, blood vessels, and blood work together
• Distributing oxygen and nutrients
• Transporting waste to excretory organs
• Distributing water, electrolytes, and hormones
• Providing infrastructure for the immune system
• Regulating temperature
• An ideal system avoids excessive heat and CO2

Heart Problems

• Systolic dysfunction is pump failure due to impaired contraction or squeezing
• Diastolic dysfunction is filling failure due to impaired relaxation
• Ventricles normally draw blood from the atria
• Fibrosis prevents ventricles from drawing blood
• Hypertrophic cardiomyopathy causes stiffness
• This impairs relaxation and diastolic function
• Arrhythmias can be regular or irregular
• Arrhythmias can be slow or fast which impacts filling time

Heart Failure

• Forward failure results in reduced cardiac output
• Backward failure causes congestion and fluid buildup
  • Right-sided failure causes ascites due to capillary leakage
    • Jugular pulsation and distension are seen as the right atrium fills
  • Left-sided failure causes pulmonary edema shown by dyspnea, tachypnea, and crackles
• Starling's Law states the more the heart fills, the more it pumps out
• RAAS is important for cardiovascular needs and is problematic in heart failure
  • ACE inhibitors, potassium-sparing drugs, and aldosterone inhibitors counteract RAAS
  • Heart failure can occur even when the heart is not actively pumping
• Dilated cardiomyopathy (DCM) involves weakening ventricular myocytes

Blood Composition

• Plasma makes up 55% of blood consisting of water, proteins, nutrients and hormones
• The buffy coat is 4% of blood and contains white blood cells and platelets
• Red blood cells are 41% of blood volume
• Changes in RBC count affect cardiac function
• Serum contains blood clots and coagulation factors
• Plasma contains coagulation factors
• Hematocrit measures the volumetric percentage of RBCs in the packed cell volume
• Increased hematocrit reduces plasma volume, increases RBC size or number
• Protein content of plasma correlates with hematocrit levels

Cardiac Anatomy

• The left side of heart is larger compared to the aorta
• Blood flow: vena cava to the right side of the heart, then to the pulmonary artery, lungs, and pulmonary vein
• Valves exist between atria and ventricles
  • The mitral valve (bicuspid, left atrioventricular) is on the left side
    • It closes during systole and opens the aortic valve
    • Mitral valve disease where blood flows back to the atrium (regurgitation) results in systolic turbulence
    • Aortic valve leakage causes diastolic murmurs
    • Aortic stenosis (narrowing) causes systolic murmur
    • Murmurs occur when valves should be closed but are open, or vice versa
    • Diastole involves blood being drawn into the ventricle, turbulence and vibration indicate valve issues
  • The tricuspid valve exists on the right side
    • Systolic murmur is indicative of tricuspid regurgitation
    • The valve should be open during diastole
• The annulus fibrosus is the septum between the ventricles

Cardiovascular Plumbing

• The left heart circulates blood systemically
• The right heart circulates blood pulmonarily
• Cardiac output is roughly equal on both sides, but slightly less on the right
  • 1-2% is shunted from the left via bronchial circulation
  • A small fraction of coronary circulation uses thebesian veins
• Coronary arteries originate at the beginning of the aorta
  • Most blood will be collected to veins, some blood (1-2%) goes to the left heart via bronchial blood

Systemic Circulation

• Aorta
  • The aorta descends to the iliac arteries
  • Resistance vessels are controlled by the sympathetic nervous system
• Arterial anastomoses are present
• Microcirculation occurs in capillaries and smallest venules
• Veins act as a blood reserve, holding 60-65% of blood volume
  • Vasoconstriction stops bleeding and constricts veins to push more blood into circulation
• The arterial system operates in parallel, except for the splanchnic and renal systems

Pulmonary Circulation

• Truncus pulmonalis is the main pulmonary artery
• Consists of the left and right pulmonary arteries
• Includes pulmonary capillaries
• Includes pulmonary veins to the left atria

Events in the Cardiac Cycle

• LV contraction
• Pressure generation
• Blood flows to the aorta
• Aortic elasticity
• Ventricular relaxation
• Blood distribution
• Diffusion in capillaries
• Collection to venous system
• Vena cava to right atrium
• Right atrium to right ventricle
• Right ventricle contraction
• Blood flows to pulmonary circulation
• Oxygenated blood to the left atrium
• Systole and diastole exists to avoid confusion with contraction

Blood Vessel Function

• All vessels are conduits
• Branching arteries reduce blood pressure pulsation
• Smallest arteries and arterioles are resistance arteries that regulate blood volume locally and centrally
• Capillaries and small venules are exchange vessels
• Venules can constrict to create resistance to capillary flow

Heart Failure Clinical Signs

• Veins are highly distensible, and are capacitance vessels
• 70% of blood volume is in the veins and 17% is in the arteries
  • Reduced cardiac output or blood volume loss can be due to venous contraction
• Forward failure is reduced cardiac output
  • Signs consists of weakness, fainting, low blood pressure, and pale mucous membranes
• Backward failure is congestion
  • Left side shows pulmonary edema
  • Right side shows ascites and pleural effusion

Gross Heart Anatomy

• Major structures include chambers, valves, and large vessels
• Valves are open
• Chordae tendineae prevent prolapse and can also rupture, being involved in pathogenesis of valvular diseases
  • Small chordae are fine but large pose a potential problem
• The anulus fibrosus provides electrical insulation between atria and ventricles
• The pericardium protects, it builds the myocardium as an immune and mechanical barrier using a slippery viscous fluid
  • If the pericardium fills, the heart cannot beat

Cardiac Myocyte Ultrastructure

• Cardiac muscle differs from skeletal
• Each myocyte attaches to multiple cells which will ensure functionality if disruption occurs
• Desmosomes allow for mechanical connection
• Gap junctions allow ion flux for contraction
• Anulus fibrosus allows atria to contract separately from ventricles

Cardiac Myocyte and Sarcomere Structure

• Myocytes are packed with myofibrils which consist of sarcomeres
• The sarcomere acts as the basic contractile unit
• The sarcomere is the contractile unit during Contraction
  • Sarcomeres shorten
  • Calcium initiates shortening
  • Contraction proportional to number of cross bridges

Coronary Arteries

• Left and right branches exist
• Ostium sinus of Valsalva
• Blood flows in diastole
• Most blood returns to right atrium
• Drainage exists via thebesian veins

Changes in Heart Muscle

• Hypertrophy involves thickening:
  • Eccentric hypertrophy is volume overload with sarcomeres added, seen in dilated cardiomyopathy
    • Stress is increased in the wall
  • Concentric hypertrophy is pressure overload that adds sarcomeres side by side
• Volume overload involves dilation of chambers
  • Starling's law of the heart applies
• Hypertrophy can increase cell size or create numeric growth (hyperplasia)
• Decompensation leads to symptoms and eventual failure

Cardiac Conduction System

• The SA node, AV node controlling electrical impulses, His bundle, bundle branches, and Purkinje fibers make up the system
• Electrical conductance is measured by the ECG
• The sinus node causes the P wave of atrial contraction
• A delayed PR interval indicates AV block
• The QRS complex indicates ventricular myocyte activation
• Repolarization of the T ventricular

Cardiac Cycle

• Events are mechanical during each heartbeat
• All chambers are relaxed at the end of diastole

Atrial Systole

• The atria contributes 20% of ventricular filling
• The end diastolic volume (EDV) is ventricular volume at the end of diastole
• The end-diastolic pressure (EDP) is ventricular pressure at the end of diastole
• Atrial fibrillation might not always show symptoms and it can be treated with surgery or catheter

Ventricular Systole

• Pressure rises sharply
• Atrioventricular valves close which makes the S1 heart sounds
• Isovolumetric contraction occurs
• Aortic valve will open
  • Allows ventricular ejection which involves a rapid phase and a reduced phase
• Contraction ceases
• Repolarization begins
• Aortic valve closes which creates the dicrotic notch
• Semilunar valves make the S2 heart sound

Heart Sounds

• Sounds between systolic consist of murmurs, shown by lap-shh-dap
• Sounds between diastolic involves mitral stenosis and poor survival rates
• Lap-dap indicate S1 and S2
• S3 and S4 indicate gallop sounds
  • Gallop sounds indicate ventricular stiffness in cats

Diastole: Relaxation

• Ventricles rapidly relax
• Isovolumetric relaxation (Plv > Pla) occurs, AV valves open for rapid ventricular filling
• If EDP is high an S3 can be heard
• Diastasis is the period between rapid filling and atrial kick
• The second phase of ventrical filling is atrial systole
  • Stiff ventricles can results in an S4 sound
• As ventricles relax the atria chills which prolongs diastasis

Cardiac Chamber Pressure

• Blood pressure is measured in blood consisting of systolic and diastolic arterial pressure
  • Systolic should match with ventricular systolic pressure
  • Ventricular diastolic pressure is below arterial
• A mean arterial pressure (MAP) calculates average pressure
• Systolic and diastolic pressure equals the pulse pressure
• Tricuspid regurgitation can result as right atrial pressure increases

Managing Cardiac Output

• CO=HR*SV: Cardiac output equals heart rate times stroke volume
  • Cardiac output is the amount of blood pumped in one minute
  • Stroke volume is the volume of blood expelled from one chamber during one stroke Factors of the heart include
  • Heart rate
  • Myocardial contractility
  • Preload
  • Afterload

Preload

• Volume of blood filling the heart
  • Hypovolemia is preload affected
• If the patient has tachycardia analyze levels
  • Give fluids to hypovolemic patients not on tachycardia
  • Take an x-ray to visualize size

Afterload

• Resistance of blood flow coming out of the heart
  • CO is affected with aortic stenosis
• Improve with vasodilators

Heart Beat Regulation

• Cardiac output equals heart rate times stroke volume
• Heart rate control occurs via the autonomous nervous system
• Sympathetic controls the sinus rate and it increases energy levels
• Parasympathetic acts as brakes

Parasympathetic/Vagus Effects

• Usually dominates
• Parasympatholytic drugs increase HR substantially
• Short postganglionic fibers and cholinesterase regulate beats
• Adjust with adrenaline or atropine in the sympathetic system

Sympathetic Effects

• Increase heart rate, contractility, conduction velocity, and relaxation

Stroke Volume

• Stroke Volume = EdiastolicV – EsystolicV
  • Preload is increased and volume is decreased

Fran-Starling Law of Heart

• Venous return increased force of contraction
• Reducing ESV means increase contraction force

Afterload

• Resistance of blood that exists Contractility
• Physiological effects of noradrenaline and adrenaline

Preload

• Constant, not constant or variant

Heart Failure

• Differs from heart disease
• Inability to elevate pressures
• Circulatory failure: heart, blood volume and Oxygen levels
• HF: syndrome resulting from structural issues

Heart Failure Classification

• Congestive heart failure: backward: - Left-sided - Right-sided
• Forward: reduced cardiac output: - Syncope and hypotension

Compensation

• Has 4 mechanisms
• Reduced tone, high tone, remodeling

RAAS

• Renin, angiotensin and aldosterone
• Aldosterone is an adrenal hormone
• It involves mineralcorticoids, sex hormones and glucocorticoids