106. Cardiac Flashcards
(37 cards)
blood supply to heart to support its function
right and left coronary artiersleft coronary is dominant—-circumflex branch around atrioventricular groover and paraconal interventricular branch supplies and divides the ventricles
eqn for SV
SV = EDV-ESVSV is the major determinant of cardiac output and is dependent on preload (end diastolic volume and end diastolic pressure), after load (systolic wall stress), contractility (inotropic state/SNS stimulation–beta influence)
eqn for CO
CO= SV x HRSV is the major determinant of cardiac output and is dependent on preload, after load, contractility
phases of a cardiac cycle pressure-volume curve
2 filling phasesan isovolumetric contraction phasean ejection phasean isovolumetric relaxation phase
what are the determinants of preload
determinants in preload reside within the circulation NOT the heartdepends on end diastolic volume and pressurewhich dependent on mean filling pressure (blood volume or circulating volume)—-direct relationship with preload–vascular resistance–inverse relationship with preload
after load and LaPlace relationship
afterload depends on systolic wall stressSWS = Psys x (ventricular radius/ventricular wall thickness)thus after load is affected by changes within the heart (cardiac remodeling radius and thickening) AND outside even (Psys)after load has an INVERSE relationship to SV
what is vascular resistance a function of
–degree of vasoconstriction (vascular radius)–viscosity of the blood (HCT)
suture pattern preferred for closure of large arteries (aorta, pulmonary vein and atrial wall)
–continuous horizontal mattress–oversewn with simple continuous3-0 to 6-0 PTFE or braided polyestertaper point needle
recommendations for inflow occlusion times
<4 minutes —preferably 2 minutes or less in a normothermic patient to minimize the risk of cerebral injury and ventricular fibrillationup to 4 minutes in hypothermic patient (32-34 C) but risk cardiac arrest increases
components of a heart-lung machine for cardiopulmonary bypass
- 3-5 pumps2. temp controlled water bath3. oxygen blender4. gas flowmeter5. anesthetic vaporizervenous blood to machine (gravity dependent) or shed blood in surgical field is aspirated and connected to machine–> blood is pumped through membrane type oxygenator and heater/cooler water bath is used to control body temp–>returns to patient with a centrifugal pump
prior to bypass, animal must undergo what procedure
complete anticoagulation by administration of heparinmonitored with ACT (normal is < 150 seconds)
end goals of cardiopulmonary bypass
MAP 50-70 mm Hgvenous oxygen saturation >70%normal lactateperfusion should be kept at the lowest flow possible to meet goals
major complications with cardiopulmonary bypass
–hemorrhage–hypoxia–circulatory collapse–cardiac arrythmias–low urine output–electrolyte and acid/base abN
most common congenital heart defect seen
patent ductus arteriosus 25-30%left 6th aortic arch remains patentnormal function is to direct venous blood away from collapsed fetal lungs, should close within a few days of birth bc once first breath is taken blood should go to lungscauses left to right shunting and volume overload and dilation of the LEFT side of the heart (accompanied by MR)
when do reverse PDAs occur
RIGHT to left shunting occurs if pressures within the RIGHT side of the heart (pulmonary arteries going to the lung) INCREASE as with pulmonary hypertensionreverses flow R to leftdifferential cyanosis, polycythemia (renal hypoxia stimulates EPO release)Eisenmengers syndromerCHFDO NOT LIGATE!tx phlebotomy or hydroxyurea to depress bone marrow (treating polycythemia)
sex predilection for PDA
females 3:1
physical exam findings for PDA
continuous heart murmur at left hear base+/- thrillBOUNDING hyperkinetic peripheral pulse (from decreased or low diastolic pressures)+/- murmur associated with mitral regurgitation
options for surgical treatment for PDA
TREAT HEART FAILURE FIRST!TREAT EARLY—70% die within the first year of life without treatmentMI percutaneous embolization with Canine ductal occluder (Amplatzer) or Thrombogenic CoilsOPEN Surgery (> 8 weeks of age)Circumferential silk ligaturesPlacement of hemoclips across PDADivision and oversewing—not often done
what is the most likely reason for diminished or weak peripheral pulse pressure
poor SV (stroke volume) which is the difference in Psys - P diastolic
anatomy for open PDA ligation
left 4*-5 lateral thoracotomyvagus nerve (lies onto of PDA) and phrenic nerve+/- left persistent vena cava (retract with vagus n)–do not ligatesilk ligation preferred over hemoclips due to residual flow and recanalization
outcome with surgical treatment of PDA
open ligation success 94% (mortality < 7%)complications < 10% (proportional to experience)hemorrhage is the most life threatening complicationsresidual flow/recanalization < 2%PDA is curative but secondary heart changes (dilation and MR may persist)MI approaches similar outcome: slight lower success with thrombogenic coils (86%) and coil migration complication is still low
Branham reflex
upon ligation of PDA, diastolic P increasedecrease in HR (may need to treat with anticholinergics)increase in BP
Breed associated with tetralogy of fallot and components of the disease
KEESHOUNDS–pulmonic stenosis—VSD (perimembranous)–destropositioned (overriding) aorta–right ventricular hypertrophyRIGHT to left shuntingmost predominant clinical finding is cyanosis that is UNresponsive to oxygen supplementationalso hypoxemic, polycythemic
types of pulmonic stenosis
–valvular (most common)–fusion or dysplasia (80%)–supravalvular–subvalvular–infundibular (muscular)Bulldogs, Boxers, Beaglebuldogs and boxers may have concurrent left aberrant coronary artery! risk rupture if balloon is too big!PRESSURE overload of RIGHT heart (concentric hypertrophy)
