106. Cardiac Flashcards
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)
how is severity of pulmonic stenosis assessed
modified Bernoulli equationpressure change across valve = 4 V squared(measure velocity on echo across the valve)Severity determined by pressure gradientMild up to 49 mmHgModerate 50 – 100 mmHg (intervene with >80 mm Hg)Severe >100 mmHg
treatment options for pulmonic stenosis
—balloon dilatation valvuloplasty***MIleft 4-5th lateral thoracotomy—pulmonary valvulotomy–thru pulmonary arteriotomy and brief inflow occlusion–pulmonary valvulectomy–thru pulmonary arteriotomy and brief inflow occlusion–patch graft valvuloplasty (pericardium, PTFE)–thru pulmonary arteriotomy and brief inflow occlusion–transventricular pulmonic dilatation valvuloplasty
outcome with surgical repair of pulmonic stenosis
palliative not curativeballoon valvuloplasty decreases risk of sudden death by 50%better prognosis for mild cases PS
ventricular septal defects
most common congenital heart disease in cats; only 10% in dogsincomplete development of inter ventricular septum (most often perimembranous portion)causes left to right shunting (UNLESS high pulmonary pressures—pulmonary hypertension or Eisenmengers syndrome and leads to R–>L)right sternal systolic murmurvarying degrees of left or biventricular enlargement
4 pathological consequences of a hemodynamically significant VSD
–low velocity shunting left to right 2 m/sec)–left sided pulmonary overcirculation on rads–left sided eccentric hypertrophy (dilation)high shunt velocity but low or normal pulmonic ejection is hemodynamically restrictive and does not require surgery
treatment for VSD
- pulmonary artery banding –left 4th lateral thoracotomyPALLIATIVEincreases right sided pressure to decrease pressure change or gradient across the defectgoal is to reduce diameter by 2/32. right 5th lateral thoracotomy close defect with PTFE or Dacron cardiovascular graft (requires bypass)
atrial septal defects
uncomplicated: shunt left to rightshunt flow >0.45 m/sec is significanttreatment 1. OPEN: pericardial graft (requires cardiac bypass) RIGHT 5th lateral thoracotomy, right arteriotomy2. MI: amplatzer septal occluder
list treatment options for systemic/pulmonary shunts to treat tetralogy of fallot
Encourage L–>R shunting (BT-P-W-G): REQUIRES BYPASS1. Blalock-Taussig anastomosis - L subclavian artery to pulmonary artery or ***modify to take portion of L subclavian and connect aorta to pulmonary artery 2. Potts anastomosis - Side-to-side anastomosis of the aorta to pulmonary artery3. Waterson–aorta to R pulmonary artery4. Glenn–venocaval to pulmonary arteryother options: fix VSD (occluder or graft)fix PS (balloon, patch graft, open valvuloplasty, -ectomy, -otomy)
Cor triatriatum
CHOW CHOW—dexter (right)persistent membrane that divides either right or left atrium into two chambersright: obstructs Cd vena cava (ascites)left: obstruct pulmonary veins (pulmonary edema)most common clinical presentation: ASCITES AT YOUNG AGE and caudal systemic venous congestionsurgery RIGHT 5th thoracotomy, membranectomy through right arteriotomy, brief inflow occlusion
two surgical options for mitral regurgitation
- valve repair (preserves myocardial function better and no prosthetic BUT variable results and less certain durability, difficult to perform); ring annuloplasty or resect prolapse leaflet2. valve replacement (easier to perform, complete correction for valve BUT prosthetic foreign body and render valve nonfunctional)—bioprosthetic (less thrombogenic) vs mechanical valve
most common cardiac neoplasms in dogs vs cats
dogs—HSA (right atrial appendage common, pericardial effusion/tamponade)cats—LSA and metastatic dz
treatment options for right atrial appendage masses (HSA)
palliative options:–open resection (RIGHT 5th or median sternotomy)–open pericardiectomy–thorascopic resection +/- pericardiectomycase report used free patch pericardium for friable atrial tissue and reinforce closureMST HSA with palliative surgery 4 months (WITHOUT chemopericardiectomy alone does NOT prolong survival
most common diagnosis for aortic body tumor
80% chemodectomasBoxers, Bulldogs, Boston Terriershighly vascular, slow growing, locally invasivepericardiectomy can be palliatively
