Chapter 106 Cardiac Surgery

Question 1

VSDs classified according to anatomic location. What are classifications and which type is most common?

Answer 1

Muscular or membranous.

Membranous most common.

N.B. VSD = 12% canine congeital heart defect, one of most common in cats!

Question 2

Closure of PDA may resut in a reflex - what is it called and what is the effect?

Answer 2

Branham reflex (suspected to be to do with cardiac baroreflexes)

Hypertension and bradycardia

Tx with glyco or atropine

Question 3

List 8 reported cardicac neoplasia in dogs

Answer 3

• Haemangiosarc
• Chemodectoma
• Ectopic thyroid
• Finrosarcoma
• Fibroma
• Chondrosarcoma
• Rhabdomyosarcoma
• Myxoma

N.B. Not mesothelioma

In cats usually lymphoma or metastatic.

Question 4

What is the recommended time limit for aortic cross clamp?

Answer 4

90 mins

Question 5

What are surgical indications for ASD?

What surgical options?

Answer 5

• Septal shunt flow velocity > 0.45 m/s (N.B musch lower value than eg pulmonic stenosis or VSD)

Sx:

• Open repair (R atriotomy) with autogenous pericardium (N.B. sinus venosus defect (with abnormal pulmonary vein anatomy) needs careful planning to ensure ‘aberrant’ pulmonary vein drains into L atrium.
• ACDO reported for ostium secundum defects.

AV block is a post-op risk (same with VSD repair)

Question 6

What is the formula for Pulse pressure? And therefore what factors might influence pulse pressure

Answer 6

P_p = SV/C_A (where C_A = compliance of large elastic arteries)

Low SV of poor compliance –> low Pp

High PP can be due to diastolic run off e.g. with PDA or aortic insufficiency

Question 7

In what breed is tricuspid dysplasia hereditary?

Surgical indication?

Sx options?

Anti-coagulation aims?

Answer 7

• Labs
• Severe tricuspid regurg = indication for sx
• Tricuspid valve replacement
• INR 2.0-3.0 (N.B. lower than mitral valve replacement which is 2.5-3.5)

Question 8

What are surgical indications for mitral regurg?

And contraindication?

Answer 8

• Diuretic dependedn CHF
• Significant LV remodelling w activity intolerance
• Progressive LA dilation
• Chnages in systolic funtion over time

Contraindication: severe chronic inflammatory airway disease +- tracheal collapse.

Question 9

Whats is MST for excision of cardiac haemangiosarc without chemo

Answer 9

4 months

N.B.Pericariectomy without tumour excision does not prolong survival!

Question 10

What is the reported rate of major complications in epicardial and transvenous pacemaker placement?

Answer 10

25% major with epicardial (8% intraop mortality), 13% with transvenous

Question 11

What is the difference between passive and active epicardial pacemaker fixation?

Answer 11

Passive = button liek ending applied to epicardium (what we have in QMH)

Active = screw-type end that penetrates myocardium.

Question 12

List 3 ‘unusual’ findings in rverse (R –> L) PDA

Answer 12

• Differential cyanosis
• No murmur
• Polycythemia

Question 13

Where do the left and right recurrent laryngeal nerves originate (ie at what level, anatomically)?

Answer 13

Left recurrent laryngeal originates at level of ductuse arteriosum.

Right recurrent laryngeal originates at level of right subclavian (i.e. shorter)

Question 14

List 4 surgical indications for DCRV

List 2 surgical techniques (and approaches). N.B. Sx palliative

Answer 14

1. Pressure gradient >50 mmHg (n.b. less well tolerated that pulmonic stenosis. Sx indication for pulmonic stenosis is gradient >60 mmHg)
2. Worsening tricuspid regurg
3. Severe execise intolerance
4. Syncope

N.B Refractory CHF and AF = poor surgical canidates.

Surgical techniques:

1. Excision of fibromuscular tissue (via ventriculotomy (median sternotomy) or atriotomy (R 5th ICT))
2. Patch graft across RVOT (median sternotomy or L ICT)

Question 15

List parameters that are continuously and periodically monitored during bypass:

Answer 15

Continuously:

• Arterial BP
• Central venous pressure
• Oesophageal and rectal temp
• ECG
• ET CO₂

Periodically:

• Blood gases (arterial and venous)
• Na⁺, K⁺, ionized Ca²⁺
• Lactate
• HCT
• TP
• Activated clotting time (=tests intrinsic + common pathways. Contains beads that activate factor 10)

Question 16

What species breeds get congenital mitral valve dysplasia?

What abnormalities can be seen?

Answer 16

Cats and large/giant breed dogs

• Short thick leaflets
• Cleft leaflets
• Chordae malformations
• Malpositioned papillary muscles

Mitral regug usually results from restrictive leaflet motion + secondary annular dilation.

Question 17

How is inflow occlusion achieved?

Answer 17

Touriques around caudal vena cava, cranial vena cava and azygous vein (if approached from R ICT can ensnare Cr VC and azygous caudal to division).

Watch out for phrenic n.

Question 18

When is differential cyanosis seen?

Answer 18

Reverse (R –> L) PDA.

i.e. de-oxygenated blood flowing out via pulmonary artery –> bypasses lungs via PDA –> descending aorta.

Question 19

Label the diagram

Answer 19

Question 20

What is anticoagulation aim after mitral valve replacement?

Answer 20

Duration based on valve type (life long if mechanical, 3 months if bioprosthetic).

Aim for INRof 2.5-3.5 (international normalised ratio, based on prothrombin time)

Question 21

What are the major and minor criteria for diagnosis of infective endocarditis?

Answer 21

Major:

• Positive blood culture of known causative agent at different time points
• Characterisitc echo findings (i.e. vegetative lesion on valve

Minor:

• Known predisposing heart conditions
• Persistent fever
• Arterial embolic events
• Immune complex conditions
• Positive serology for known causative agents e.g. Bartonella

Question 22

What is surgical mortality rate?

Factor associated with increased risk post-op mortality?

Factors associated with increased risk of rupture (most common cause of operative mortality)?

Answer 22

Surgical mortality: 0-7%

Assoc w post-op mortality: CHF

Assoc w rupture: less surgeon experience, older animal

Question 23

List 5 breeds at risk for aortic stenosis

Answer 23

Large breed: Golden retriever, Boxer, Rottweiler, Newfoundland, Bull Terrier, Bouvier

Question 24

List following post-bypass recovery targets:

• CVP
• HCT

Answer 24

• CVP: 4-10 mm Hg
• HCT >30%

Question 25

What is a normal volume of pericardial fuid in the dog?

Answer 25

0.5-1.0ml total

Question 26

Before cannulation and initiation of bypass, patient must undergo anti-coagulation. What dose is recommended. What test is used to measure efficacy + what is target value?

Answer 26

300-400 U/kg heparin iv ACT to monitor, aim for ACT \>480s

Question 27

When is PDA closure contra-indicated?

Answer 27

R --\> L shunt or bidirectional shunt

Question 28

Which species get cor triatriatum dexter and which sinister? Breed predilection?

Answer 28

Dogs = dexter. Chow chows Cats = sinister

Question 29

Pulmonic stenosis is usually valvular (can be supra or sub-valvular also). More than 80% of dogs w valvular stenosis have some degree of valve dysplasia. Based on valve anatomy, valvular pulmonic stenosis is classified into two groups - what are they?

Answer 29

Type A valvular pulmonic stenosis: Normal annulus diameter (aortic:pulmonary ratio ≤1.2) Type B valvular pulmonic stenosis: Hypoplastic annulus diameter (aortic:pulmonary ratio ≥1.2)

Question 30

List the three classifications of ASD (which most common?)

Answer 30

* **Ostium Secundum** - located in the center of the atrial septum (most common type) * **Coronary Sinus** - incomplete separation between coronary sinus and left atrium. * **Sinus Venosus** - located near top of atrial septum/juntion with cava. Frequently associated with abnormal connection of the right pulmonary vein(s) to the right atrium instead to the left atrium

Question 31

List two methods for venous cannulation during bypass:

Answer 31

* Bi-caval (if right thoracotomy!) * Cavoatrial (can be performed via right or left thoracotomy. Via R auricular appendage - one port directed into CVC other into atrium) * Jugular (if left thoracotom i..e cant do bicaval..)

Question 32

Between which intercostal spaces is heart located?

Answer 32

3-6

Question 33

What is the only predictor of survival in cases with aortic stenosis?

Answer 33

Severity of pressure gradient at diagnosis. i.e. surgery, balloon valvuloplasty, medical tx with beta-blockers do not affect survival. Life expectancy 4-6 years.

Question 34

What surgical treatment options exist for aortic regurg?

Answer 34

Heterotopic (=out of usual place) aortic valve implantation (porcine bioprosthetic). I.e. valve implantation by end to end anastomosis of descending aorta! Performed by vascular occlusion of descending aorta (keep to \<13 mins - risk of spinal cord injury) Only single canine case report re outcome - lived for 5+ years

Question 35

What treatment can be considered for aortic body tumours?

Answer 35

Pericardiectomy. Prolongs survival, regardless whether effusion present or not 700d vs 42d!

Question 36

How many papillary muscles does th eleft ventricle have?

Answer 36

Two (each receives chordae from each leaflet i..e one papillary muscle attaches to both valve leaflets)

Question 37

What four abnormalities constitute tetralogy of fallot?

Answer 37

* VSD * Pulmonic stenosis * Overriding aorta * R V hypertrophy Pathophys can vary from 'haemodynamically restirtive' --\> balanced (analagous to VSD after pulmonary banding) --\> severe stenosis and R --\> L shunting

Question 38

Mitral valve anatomy: Two valve leaflets septal (anterior) and mural (posterior/parietal). Each leaflet structurally divided into three distinct portions; A1, A2 and A3, and P1, P2 and P3. There are three orders of chordae tendinae. How are they defined?

Answer 38

Primary: Leaflet edge --\> Papillary muscle Secondary: Leaflet underside --\> Papillary muscle Tertiary: Leaflet underside --\> Ventricular wall

Question 39

How many vale leaflets does each heart valve have?

Answer 39

Tricuspid: Two Pulmonary: Thee (semi-lunar) Mitral: Two Aortic: Three (semi-lunar)

Question 40

What proportion of cardicac tumours are haemangiosarcomas? What % of splenic haemangiosarcs have cardiac neoplasia? What % of cardiac endothelial tumour have splenic haemangiosarc?

Answer 40

40-70% 9% (golden ret x10 more likely to have ecardiac involvement vs other breeds) 30%

Question 41

What is the most important cause of aortic regurg?

Answer 41

Infective endocarditis (less frequently due to degenerative valve changes, annulus dilation, or associated with congenital defects (VSD, subvalvular stenosis)

Question 42

At what body temperature is effective cardiac rhythm re-established?

Answer 42

37º

Question 43

List two options (vessels) for arterial cannulation.

Answer 43

Femoral artery or carotid artery | (size 8 - 14 Fr cannulae used)

Question 44

What approach provides best acces to cranial and caudal cava, azygous vein and R atrium?

Answer 44

R intercostal

Question 45

What is the significance of the interventricular grooves?

Answer 45

Represent the path of coronary arteries (Called *sinusoidal* and *paraconal*)

Question 46

List 2 advantages and 3 disadvantages of mitral valve replacement (bileaflet tilting disc or bioprosthetic)

Answer 46

_Advantages:_ * Easier to perform * Complete correction of regurg. _Disadvantages:_ * Patient BW has to be \>10kg re size of valve. * Thrombogenic (lifelong anticoag in mechanical valve (56% catastrophic thrombosis despite warfarin), 3 months in bioprosthetic) * Inflammatory pannus (bioproshtetic)

Question 47

What is Eisenmenger syndrome?

Answer 47

VSD + R --\> L shunting due to pulmonary hypertension

Question 48

List 2 advantages of inflow occlusion vs bypass List 3 disadvantages:

Answer 48

_Advantages:_ 1. Less equipment/complexity 2. Fewer CVS metabolic, haematological derangements _Disadvantages:_ 1. Limited time 2. Motion 3. Lack of fall back if procedure taking longer

Question 49

List 3 broad options for management of PDA

Answer 49

* Surgical ligation * Amplatz Canine Ductal Occluder (ACDO) (=nitinol wire mesh. Generally need 5 Fr catheter in artery) * Coil embolization (trans-arterial or transvenous reported - venous allows bigger size)

Question 50

In which order do ion channels open in generation of cardical action potential? Which ion initiates contraction of cardiomyocyte?

Answer 50

1. Na²⁺ 2. K 3. Ca²⁺ Ca²⁺ entry into cell --\> contraction

Question 51

what % congenital heart defect does pulmonic stenosis account for? List 2 breedsthat commonly present with type B (hypoplastic annulus) pulmonic stenosis

Answer 51

20% of congenital heart defects i.e common English Bulldog and Boxer N.B. also breeds that at risk for anomalous left coronary (L coronary originates from single R coronary ostium meanign L coronary courses around R VOT... implications re ballooning

Question 52

List 3 techniques to manage intra-op PDA rupture

Answer 52

* Jackson Henderson technique (i.e. dissect DV path from ventral to dorsal aorta. do this cranially and caudally to PDA and pass suture between so that ultimate suture lies behind PDA, without having to dissect directly behind ductus. * Buttressed mattress sutures * Divide and over-sew

Question 53

How is severity classified for aortic stenosis? Why is it relevant?

Answer 53

Mild: pressure gradient 16-50 mmHg Moderate: pressure gradient 50-80 mmHg Severe: pressure gradient \>80 mmHg Relevant because this is the only factor associated with outcome (i.e. not affected by surgery or balloon valvuloplasty)

Question 54

Surgical options for cortriatriatum?

Answer 54

Membranectomy (open or via intravascular/hybrid)

Question 55

How is coronary dominance determined? What is the usual coronary dominance in dogs? And in cats?

Answer 55

Indicated which coronary artery supplies the subsinusoidal interventricular groove. Dogs usually left coronary dominance, cats usually right coronary dominance.

Question 56

What is the desired HCT during bypass?

Answer 56

25-28% (oxygen delivery and whole body oxygen uptake decrease when HCT \<18%)

Question 57

PDA is most common congenital heart defect - what % of congenital malformations does it account for?

Answer 57

25-30%

Question 58

What is administered to reverse heparin, what dose/target, what are the side effects?

Answer 58

Protamine sulfate 5 mg/min until ACT \<150s S/e: hypotension, pulmonary vasoconstriction.

Question 59

Label the diagram

Answer 59

Question 60

List 4 indications for surgical intervention for pulmonic stenosis. List 3 "treatment" techniques Aim of treatment?

Answer 60

_Indications for surgery:_ 1. Presence of tricuspid regurgitation 2. Severe stenosis 3. \>60 mmHg pressure gradient across defect 4. Clinical signs present _Treatment techniques:_ 1. Balloon dilation valvuloplasty (intravascular/hybrid - nb coronary artery anatomy/rupture risk. Tx of choice for Type A. \<10% mortality) 2. Surgical pulmonic dilation valvuloplasty (inflow or CPB, commissurotomy or excision. Doesnt address infundibular hypertrophy/annulus hypoplasia - useful for anaomalous L coronary cases.) 3. Open pulmonic patch graft valvuloplasty (Autogenous pericardium or PTFE path. Inflow (L 5th ICT - to tourniquet Cd Cava) vs CPB (median sternotomy). 30% mortality rate. CONTRAINDICATED if anomalous L coronary!) _Aim:_ Pressure gradient \<50 mmHg

Question 61

Label diagram of bypass circuit (i.e. heart-lung machine + bypass circuit)

Answer 61

_Heart-lung machine:_ Pumps, heater/cooler, oxygenator, gas flowmeter, anaesthetic vapourizer. _Bypass circuit:_ Resevoir, pump, membrane oxygenator, heat exchanger, heater/cooler water bath

Question 62

List three interventios for management of VSD

Answer 62

* **Pulmonary artery banding:** usually 2/3rds reduction in vessel diameter, measure pressure distal to band, ideally \<30 mmHg. Palliative. Complication = overtightening + flow reversal * **Open repair:** (CPB, access via R atrium or R ventricle) with PTFE or Dacron graft - care re caudal margin as major conduction bundles located there. * **Intravascular/hybrid:** ACDO reported for muscular VSD

Question 63

Physiologically speaking, how does AV node slow action potential?

Answer 63

AV node cells lack voltage dependednt Na²⁺ channels (i.e. *fast* channels)

Question 64

What are the three most common congenital heart defects in dogs?

Answer 64

PDA, pulmonic stenosis, aortic stenosis

Question 65

Double chambered R ventricle --\> inflow obstruction of R ventricle. What is proposed mechanism of formation? N.B. in humans usually associated with another abnormality and same suspected in dogs

Answer 65

Often associated with VSD. Mechanism suspected = dorsal displacement of moderator band + turbulent flow from VSD (VSD closes) --\> hypertrophic obstructive area mid ventricle

Question 66

Body temp should not be allowed to fall below 32º during inflow occlusion. Why?

Answer 66

Increased risk of ventricular fibrillation

Question 67

Particular clinical signs in cor triatriatum dexter and why?

Answer 67

Ascites, venous distensionin caudal half of body. Because membrane forms between *caudal* vena cava and tricuspid valve, i.e. flow from cranial cava unaffected.

Question 68

What are surgical indications for Tetralogy of Fallot? Surgical options?

Answer 68

_Indications:_ * Debilitating exercise intolerance * Polycythemia (HCT \>70%) * Resting hypoxaemia _Options:_ * Isolated **correction of pulmonic stenosis** * Creation of s**ytemic to pulmonary shunt** i.e. aorta/subclavian --\> pulmonary artery. e.g. Blalock-Taussig * **Open repair** (bypass inc VSD closure and pulmonic patch graft). Curative

Question 69

What is the most common location of pulmonic vs aotic stenosis (sub-, supra-, or valvular)?

Answer 69

Pulmonic stenosis usually valvular, aortic stenosis usually subvalvular

Question 70

Outflow portions run parallel to each other. At what anatomical level does separation occur?

Answer 70

At the level of the septal mitral valve leaflet (specifically called mitral curtain)

Question 71

What is the time limit for planned circulatory arrest (i.e. inflow occlusion) in normothermic patient? And in hypothermic patient:

Answer 71

Normothermic: \<2 min Hypothermic (32-34º): \<4 mins

Question 72

What is the ventricular conducting system called?

Answer 72

His-Purkinje conduction system

Question 73

What does Waterston's groove represent?

Answer 73

The embryologic separation between the right and left atria.

Question 74

List key steps in mitral valve replacement

Answer 74

* ICT * L atriotomy * Septal leflet excised (not mural to preseve myocardial function) * Pre-place buttressed sutures through annulus. * Place sutures through sewing ring of replacement.

Question 75

What three variables determine SV?

Answer 75

Preload, afterload and contractility _Preload:_ mean filling pressure (i.e. blood volume and venous vascular tone) and vascular resistance i.e. determinants of pre-load are outside the heart. _Afterload:_ Systolic wall stress. Predicted by LaPlace relationship (/formula) SWS = (P_sys x ventricular radius)/ventricular wall thickness i.e. beat-to-beat afterload determined by systolic pressure. On chronic basis, cardiac remodelling affects afterload. _Contractility:_ Largely a function of amoiunt of sympathetic (ß) influence on heart.

Question 76

What anatomic reference point indicates level of phrenic nerves?

Answer 76

Coronary groove

Question 77

Where does the azygous vein drain into?

Answer 77

The cranial cava (close to junction w right atrium)

Question 78

How is the left atrium approached?

Answer 78

L or right intercostal

Question 79

List values for the following bypass targets: * Body temperature * Venous oxygen saturation * MAP * PaO2

Answer 79

* Body temperature: 25-28º (if \>10kg), 15-18º (if \<10kg) * Venous oxygen saturation: \>70% * MAP: 50-70 mm Hg * PaO2: \>120 mm Hg

Question 80

How is the RIGHT VOT (ventricular outflow tract) accessed?

Answer 80

L ICT or median sternotomy

Question 81

In what two breeds has heritable basis for PDA been established? Sex prediclection?

Answer 81

Poodles and Welsh Corgis Females Also commoon in Keeshond, Bichon, Maltese, Yorkie, Cocker, Pom, Sheltie,

Question 82

What are the pressures in each cardiac chamber?

Answer 82

Question 83

List 3 surgical techniques for management of mitral valve leaflet prolapse

Answer 83

* Quadratic resection --\> mattress plication (cannot be used on septal leaf) * Edge to edge repair --\> suture free edge of prolapsing leaflet to free edge of opposing leaflet --\> double orifice valve. * Artificial chordae

Question 84

Which portionof annulus is corrected durign mitral valve annuloplasty.

Answer 84

Mural only. Principle is that the ural, but not septal, portion of annulus stretches. Use annuloplasty ring or CV graft materials (Dacron or PTFE).

Question 85

Which congenital heart defect has been shown to pre-dispose dogs to bacterial endocarditis?

Answer 85

Aortic stenosis

Question 86

How is cardioplegia administered and what is it made of?

Answer 86

Cross clap aorta and cannulate aortic root + instill cardioplegia (i.e. runs into coronary arteries). Cardioplegia = KCl + NaHCO_3- + heparinized blood + crystalloid. High [K⁺] --\> arrest electrical and mechanical activity of myocardium.

Question 87

List two factors that affect vascular resistance (R)

Answer 87

Degree of vasoconstriction and blood viscosity

Question 88

What are the echo findings in DCRV?

Answer 88

Hypertrophy of R ventricle with abrubt transition to normal appearing RVOT distal to obstruction (only causes R ventricular *inflow* obstriution)

Question 89

What are the criteria for haemodynamically restrictive VSD (i.e. amount of blood flow via vsd is restricted so good prognosis without surgery). What are criteria for surgery?

Answer 89

_Heamodynamically restrictive:_ * High velocity shunt (\>4.5 m/s) * Normal pulmonic ejection velocity (\<2 m/s) Large defects usually have low shunt velocity (\<3.5 m/s) and higher pulmonic ejection velocity (\>2.5 m/s) _Surgery:_ * High flow shunts (aside from echo high flow shunts may also be indicated by radiographic pulmonary vascular enlargement, L ventricular (and ?atrial) enlargement)

Question 90

List 3 indications for epicardial (vs transvenous) pacemaker necessary.

Answer 90

* Small patient size * Infection * Thromboemblic conditions

Question 91

When is pacemaker traetment indicated?

Answer 91

* High grade 2nd degree, or 3rd degree AV block * Sick sinus syndrome * Sinus arrest * Other chronic bradyarrythmias * (Lack of response to medical treatment)

Question 92

How are epicardial pace markers affixed?

Answer 92

Passive (epicardial suture) or active (screw type) ## Footnote (secured to left ventricle - avoid coronaries, close pericardium (better pacemaker contact - secure pulse generator in intermuscular pocket (under external oblique if exited via thorax (i.e. ICT approach), or under transverse abdominis is exited via diaphragm (i..e coeliotomy approach))