Cardiac surgery Flashcards
1
Q
In a study by McNamara 2023 in JAVMA, what was the rate of intraoperative hemorrhage during PDA ligation in dogs? What was the overall mortality rate?
A
Intraoperative hemorrhage: 11%
Mortality: 2%
Age, weight, and LA:Ao ratio had no impact on risk of hemorrhage.
2
Q
In a study by Moirano 2023 in VRU, what was the MST for 7-dogs undergoing hypofractionated intensity modulated radiotherapy and vinblastine treatment for management of a right atrial tumour?
A
326 days
3
Q
What is the name of the cardiac groove that demarcates the path of the coronary arteries?
A
Interventricular groove
4
Q
Which coronary artery is normally the dominant coronary artery in dogs and cats?
A
Dogs: Left.
Cats: Right.
5
Q
What are the names of the atrioventricular valves of the heart?
A
Right: tricuspid:
Left: mitral
6
Q
What is the position of the vagal and phrenic nerves in relation to the heart?
A
The phrenic nerves run over the pericardium at the level of the coronary groove, the vagus nerves run at the level of the heart base.
7
Q
At what anatomic landmarks do the right and left recurrent laryngeal nerves originate from the vagus?
A
Right: level of the right subclavian.
Left: level of the ductus or ligamentum arteriosum.
8
Q
What structures compose the AV valves of the heart?
A
Leaflets (septal and mural), chordae (primary, secondary and tertiary), and papillary muscles.
9
Q
What are the two layers of the pericardium?
A
Visceral (or epicardium), parietal (external fibrous and inner serous components).
10
Q
What is the composition of the pericardial fluid?
A
Ultrafiltrate of plasma (normal volume 0.5-1ml).
11
Q
Describe the events of the cardiac cycle.
A
12
Q
What is the stroke volume of the heart?
A
End-diastolic volume minus end-systolic volume.
13
Q
What factors determine stroke volume?
A
Preload, afterload and contractility.
14
Q
What is the Frank-Starling principle?
A
The greater the diastolic strain (preload) on the heart the more forceful the cardiac contraction.
15
Q
What is the LaPlace relationship?
A
Prediction of cardiac afterload as determined by: systolic pressure x ventricular radius/ventricular wall thickness.
Therefore increases in systolic pressure cause increases in cardiac afterload.
16
Q
What largely determines cardiac contractility?
A
The amount of sympathetic (Beta adrenergic) influence on the heart.
17
Q
What determines cardiac output?
A
Stroke volume x heart rate.
18
Q
What is pulse pressure?
A
The difference between systolic and diastolic blood pressures. Determined by stroke volume/arterial compliance.
Most likely cause of poor pulse pressure is poor stroke volume. Stiffening of the arteries can cause increased pulse pressure.
Pulse pressure is independent of MAP (e.g. can have a low MAP but normal pulse pressure).
19
Q
What is the effect of rapid diastolic run-off (i.e. PDA) on pulse pressure?
A
Elevated pulse pressure due to a drop in the diastolic blood pressure.
20
Q
What is the His-Purkinje conduction system?
A
The rapid conduction system transmitting electrical cardiac activity from the AV node to the ventricular myocardium.
21
Q
Which anesthetic agents should be avoided in patients undergoing cardiac surgery?
A
Acepromazine (prolonged hypotension), alpha-2 agonists (due to cardiac depression).
22
Q
What surgical instruments (aside from a general surgical pack) may be useful when performing cardiac surgery?
A
DeBakey tissue forceps, Metzenbaum scissors, Potts scissors, Castroviejo needle holders, angled thoracic forceps and vascular clamps (straight, angled, curved, and tangential).
23
Q
What are some common sutures used in cardiac surgery?
A
Polypropylene, PTFE, braided polyester, silk. Pledgets are useful for buttressing cardiac repairs
24
Q
What are two options for control of vascular inflow when performing open cardiac surgery?
A
- Inflow occlusion
- Cardiopulmonary bypass
25
How long can inflow occlusion of the heart be performed for?
2 minutes, or 4 minutes if mild whole body hypothermia (32 - 34 degrees).
26
How is inflow occlusion achieved?
Temporary occlusion of the azygous vein, cranial and caudal vena cavae (easiest access via a right intercostal thoracotomy).
27
Which arteries are preferred for cannulation during cardiopulmonary bypass in the dog?
Carotid or femoral
28
What does the following diagram depict?
Cardiopulmonary bypass circuit.
29
What are the two options for venous cannulation during cariopulmonary bypass?
1. Bicaval venous cannulation (required if complete diversion of blood away from the heart is required, e.g. right atrial cardiac repairs).
2. Single, two-stage cavoatrial cannula through the right auricle.
30
What are some parameters that are monitored during cardiopulmonary bypass?
1. Hematocrit: hemodilution to 25-28%.
2. Anticoagulation prior to initiation of bypass (ACT monitored every 30 minutes and kept above 480 seconds).
3. Venous oxygen saturation of 70%.
4. MAP: 50 - 70 mmHg
5. Cooling to 25-28 degrees.
6. PaO2 > 120 mmHg
7. Blood gases measured every 30 minutes and metabolic acidosis corrected through administration of NaHCO3.
31
What is the purpose of cardioplegia solution?
To protect the myocardium from ischemia during aortic cross clamping. Aortic cross clamping is performed to prevent formation of air emboli.
Contains high concentrations of K+ that arrests electrical activities and cools the myocardium (4 degrees).
32
What are some complications associated with cardiopulmonary bypass?
Post-operative hemorrhage, hypoxemia, circulatory collapse, arrhythmias, low urine output, electrolyte and acid base abnormalities.
Administration of high volumes of crystalloids should be avoided due to a generalized increase in vascular permeability (blood products are preferred).
33
What is pump lag?
Hypoxemia that is often present after cardiopulmonary bypass, secondary to pulmonary injury and increased pulmonary vascular permeability. Mechanical ventilation generally required for 4-12 hours post-operative.
34
What two structures does the ductus arteriosus connect?
The main pulmonary artery to the descending aorta. Should close a few days after birth.
35
Are males or females more likely to have a PDA?
Females, purebred dogs seem to be most commonly affected.
Heritable basis in poodles and Welsh corgis.
36
What are the two directions of flow that might occur through a PDA?
Left-to-right (most common): causes volume overload of the left heart and left ventricular and atrial dilatation, progressive myocardial deterioration, and left-sided CHF.
Right-to-left: secondary to pulmonary hypertension. Causes cyanosis and hypoxemia that are more severe in the caudal half of the body.
37
What is the prognosis for untreated PDA?
Majority of dogs die before 1 year of age.
38
What are the clinical signs associated with PDA?
1. Continuous heart murmur at the left heart base and bounding femoral pulses (typically not present with right-to-left shunting).
2. Thoracic radiographs: severe left atrial enlargement, ventricular enlargement, enlargement of pulmonary vessels, and dilatation of the descending aorta.
3. ECG: spiked R waves.
4. Echocardiography: confirmatory.
39
What are the options for treatment of a left-to-right PDA?
1. Surgical ligation (>8 weeks of age).
2. Percutaneous occlusion with embolization coils or Amplatz Canine Ductal Occluder (ACDO).
40
What are contraindications of PDA ligation?
Right-to-left or bidirectional PDA.
41
What are options for surgical ligation of a PDA?
1. Standard suture ligation.
2. Jackson-Henderson technique (may be associated with higher residual flow compared to standard ligation; 53% v 21%).
3. Hemostatic clips (not recommended due to risk for residual duct flow and recanalization).
42
What is the preferred approach for a PDA?
Left 4th intercostal thoracotomy.
43
If a persistent left cranial vena cava is identified during approach to a PDA should it be ligated and divided?
No, it should be gently retracted with the vagus nerve.
44
Describe the surgical approach to PDA.
45
What is the Branham reflex?
Decrease in heart rate and increase in blood pressure. Often observed after PDA ligation.
46
Are mitral valve regurgitation and secondary myocardial failure generally reversible following PDA ligation?
Yes, surgery is often curative in patients <6 months of age.
ACE-inhibitors and beta-blockers can be considered post-operative in cases of secondary myocardial failure.
47
What are some options for dealing with PDA rupture during surgical ligation?
1. Gentle tamponade (if small).
2. Immediate placement of vascular clamps (if large).
Following rupture standard suture ligation is often not possible. Alternative methods of closure include:
1. Jackson-Henderson suture.
2. Closure of the ductus with three or four wide biting buttressed mattress sutures (risk of residual flow, but helps to tamponade hemorrhage).
3. Division between the vascular clamps and oversew (no risk of residual flow but more technically demanding).
48
What are the two types of pulmonary stenosis?
Type A: normal annulus diameter.
Type B: hypoplastic annulus diameter (common amongst Boxer's and English Bulldogs).
49
An anomolous left coronary artery is commonly found in which breeds?
Boxers and English bulldogs.
50
Is valve dysplasia or valve fusion more common in dogs with pulmonary stenosis?
Valve dysplasia (80%).
51
What is the location of murmur with pulmonic stenosis?
Left heart base (systolic ejection).
52
When should surgery be considered for cases of pulmonic stenosis?
Presence of tricuspid regurgitation, pressure gradient across the defect of 60 mmHg or greater, clinical signs.
53
What are the treatment options for pulmonic stenosis?
1. Balloon valvuloplasty (treatment of choice for type A stenosis. Not recommended in Boxers or English bulldogs due to the risk of rupture of an anomalous left coronary vein).
2. Dilatation valvuloplasty (via arteriotomy or interventricular approach).
3. Open pulmonic patch graft valvuloplasty (either via inflow occlusion or cardiopulmonary bypass).
4. Pulmonary valvulotomy or valvulectomy.
54
What is an absolute contraindication for patch graft valvuloplasty for pulmonic stenosis?
Anomalous left coronary artery.
55
Is the outcome poorer for dogs with type A or type B pulmonary stenosis undergoing balloon dilatation?
Type B
56
Are treatments for pulmonary stenosis considered palliative or curative?
Palliative (aim to decrease systolic pressure gradient across the stenosis to less than 50 mmHg).
57
What is a double chambered right ventricle?
The presence of a fibromuscular diaphragm at the junction of the inflow and outflow portions of the right ventricle.
Often associated with a septal defect.
58
Where is the heart murmur identified for cases with double chambered right ventricle?
Left heart base (systolic ejection murmur).
59
What are the clinical signs associated with double chambered right venticle?
Signs of right sided CHF, similar to pulmonic stenosis.
60
When should surgery be considered for cases of double chambered right ventricle?
Same parameters as for pulmonic stenosis, except lower pressure gradient as a threshold (50 mmHg).
Parameters for pulmonic stenosis: Presence of tricuspid regurgitation, pressure gradient across the defect of 60 mmHg or greater, clinical signs.
61
What are treatment options for a double chambered right ventricle?
1. Excision of the fibromuscular tissue via ventriculotomy or right atriotomy.
2. Patch graft
62
What is the outcome for dogs with double chambered right ventricle?
Treatment generally considered palliative rather than curative.
63
In what breeds of dog is aortic stenosis most frequently seen?
Large breed dogs.
64
Where is the location of the heart murmur for cases of aortic stenosis?
Left heart base (systolic ejection murmur).
65
What is the sequelae of aortic stenosis?
Left CHF.
66
How is the severity of aortic stenosis classified?
Mild for pressure gradients between 16 and 50 mm Hg, moderate for those between 50 and 80 mm Hg, and severe for gradients greater than 80 mm Hg.
67
Does surgery improve the prognosis for dogs with aortic stenosis?
No. Surgery, transcatheter balloon valvuloplasty, or medical treatment with beta-blockers does not appear to affect survival.
68
What is the most common cause of aortic regurgitation?
Endocarditis.
69
What are the most prominent clinical findings associated with aortic regurgitation?
Diastolic murmur at the left heart base, and hyperkinetic or bounding arterial pulses.
70
What are the major criteria for diagnosis of infectious endocarditis?
Positive blood cultures and characteristic findings on echocardiography.
71
What are the treatment options for aortic regurgitation secondary to infectious endocarditis?
1. Antimicrobial therapy.
2. Stabilization of the cardiac disease.
3. Few surgical options, heterotopic aortic valve implantation with a porcine bioprosthetic valve has been described with good success.
72
What is ventricular septal defect?
Defect that results from incomplete development of the membranous or muscular ventricular septum.
73
What is the pathophysiologic consequences of a ventricular septal defect?
Depends on the size of the defect. Typically results in a left-to-right shunt, with overload of the left (+/- the right ventricle). Pulmonary hypertension can occur secondary to sustained volume overload with eventual reversal of the shunt (Eisenmerger syndrome) in some instances.
Concurrent collapse of the aortic cusp into the ventricular defect can worsen left ventricular overload (aortic insufficiency).
74
What is the location of the murmur with a ventricular septal defect?
Right sternum and left heart base (systolic) +/- diastolic murmur at the left heart base in cases of concurrent aortic insufficiency (to-and-fro murmur).
75
When is surgery indicated for ventricular septal defects?
High flow shunts (normally indicated by low shunt velocities <3.5 m/s across the defect, and increased pulmonic ejection velocity >2.5 m/s).
76
What are the treatment options for ventricular septal defects?
1. Pulmonary artery banding.
2. Open repair of the defect under cardiopulmonary bypass with PTFE or Dacron cardiovascular graft.
77
What is the main complication associated with pulmonary artery banding for treatment of ventricular septal defect?
Overtightening of the band resulting in reversal of shunt flow and hypoxemia. Can be prevented by monitoring pulmonary and systolic blood pressures during tightening.
78
Is open surgical repair of ventricular defects considered curative?
Yes
79
Which breed of dog is most commonly affected by atrial septal defects?
Boxer
80
In which direction does blood typically shunt in atrial septal defects?
Left-to-right, resulting in right sided CHF.
Shunt direction can reverse secondary if right atrial pressures increased secondary to CHF, pulmonary hypertension, or concurrent right sided structural heart defects.
81
Where is the heart murmur located for an atrial septal defect?
Left cardiac base (systolic ejection) due to high velocity flow through the pulmonic valve.
82
What is the treatment for atrial septal defects?
Open repair under cardiopulmonary bypass with closure of the defect using an autogenous pericardial graft.
If an atrioventricular defect (affecting the mitral valve) is present, suturing of the mitral valve or annuloplasty may be required.
83
What are the components of tetralogy of Fallot?
Pulmonic stenosis; ventricular septal defect; a dextropositioned overriding aorta; and secondary right ventricular hypertrophy.
84
What breed of dog is predisposed to Tetralogy of Fallot?
Keeshonds.
85
What are the pathophysiologic consequences of tetralogy of Fallot?
1. Large septal defect, minimal pulmonic stenosis = similar left-to-right shunting to regular septal defect.
2. Severe pulmonic stenosis = right-to-left shunt and cyanosis.
3. The septal defect and pulmonic stenosis are hemodynamically balanced.
86
What are the most prominent physical exam findings in patients with tetralogy of Fallot?
Cyanosis that is unresponsive to supplemental oxygen. Systolic heart murmur at the left heart base and right sternum.
87
When is surgery indicated for tetralogy of Fallot?
Cyanotic animals, debilitating exercise intolerance, polycythemia (hematocrit >70%), and resting hypoxemia (arterial oxygen saturation <60%).
Patients that are not cyanotic ('pink' tetralogy) may function reasonably well without intervention.
88
What are surgical treatment options for tetralogy of Fallot?
1. Surgical correction of the pulmonary artery stenosis: this risks overwhelming left-to-right shunt.
2. Modified Blalock-Taussig shunt using either the left subclavian or jugular vein as a graft between the pulmonary artery and aorta (or sublclavian artery). This creates a left-to-right shunt to counter the pre-existing right-to-left shunt.
3. Definitive repair using cardiopulmonary bypass and pulmonic stenosis patch grafting and septal defect patching.
89
What is the outcome for tetralogy of fallot following surgical intervention?
Complete resolution and normal life-expectancy.
90
What is cor triatriatum?
Uncommon congenital defect which results in persistence of an embryonic membrane in either the left or right atrium.
91
What are the two types of cor triatriatum?
Dexter: obstructs the inflow tract of the caudal (but not cranial) vena cava, causing ascites.
Sinister: obstructs the inflow tract of the pulmonary veins leading to pulmonary edema.
92
How is cor triatriatum treated?
Membranectomy via atriotomy under brief inflow occlusion or cardiopulmonary bypass. Intravascular approaches have also been described.
Surgery is considered curative.
93
What is the most frequent cause of mitral regurgitation in dogs?
Myxomatous degeneration.
May also occur secondary to dilated cardiomyopathy (functional mitral valve regurgitation) that results in dilation of the valve annulus and restrictive leaflet motion.
94
What are the predominant clinical findings associated with mitral valve regurgitation?
Systolic murmur at the left cardiac apex. Weak femoral pulses may be present. Crackles may be heard on auscultation of the lungs.
ECG changes can include atrial tachycardia or fibrillation.
95
What are the surgical options for mitral valve regurgitation?
1. Valve repair.
2. Valve replacement.
96
What are the advantages/disadvantages of mitral valve repair over replacement?
Advantages: doesn't require a prosthesis, minimally thrombogenic, doesn't require long term anticoagulation therapy, preserves myocardial function better.
Disadvantages: more variable results and less durability.
97
Are bioprosthetic or mechanical prostheses preferred for mitral valve replacement?
Bioprosthetic valves, due to the high risk of thrombosis associated with mechanical valves.
Disadvantage of bioprosthetic valves is the risk of inflammatory pannus formation, which renders the valve non-functional.
98
Describe the procedure for mitral valve replacement.
99
How is mitral valve repair performed?
Combination of annuloplasty and correction of leaflet prolapse (depending on the cause of regurgitation). Diagrams on page 2080 of Tobias.
100
What is the outcome following mitral valve replacement surgery?
Life expectancy of 5 years with the use of bioprosthetic valves or valve repair.
Catastrophic valve thrombosis and death occurred in 56% of patients when using mechanical prostheses.
101
What is tricuspid valve dysplasia?
A congenital condition characterized by a thickened, immobile septal leaflet that is tethered to the ventricular septum.
Appears hereditary in Labrador retrievers.
102
What type of murmur is present with tricuspid valve dysplasia?
Right sided systolic murmur.
103
What occurs secondary to tricuspid valve dysplasia?
Right sided CHF (although may not occur until later in life even if the regurgitation is severe).
104
What is the treatment for tricuspid valve dysplasia?
Valve replacement (repair has not been successful).
105
What are some cardiac tumours that have been reported in dogs?
Hemangiosarcoma, fibrosarcoma, chondrosarcoma, rhabdomyosarcoma, ectopic thyroid carcinoma, fibroma, myxoma, and chemodectoma.
106
What are the most common cardiac tumours in cats?
Lymphosarcoma and metastatic neoplasia.
107
What is the most common cardiac tumour in dogs? Where is it most frequently located?
Hemangiosarcoma.
Often arises from the right atrial wall.
108
Which breed of dog is more likely to have concurrent cardiac involvement in cases of primary splenic hemangiosarcoma?
Golden retrievers (11 times as likely to have cardiac involvement).
109
What percentage of dogs with primary cardiac hemangiosarcoma have concurrent splenic hemangiosarcoma?
29%
110
What is the most common clinical presentation of cardiac hemangiosarcoma?
Acute cardiac tamponade.
111
What is the MST following excision of right atrial hemangiosarcoma?
4-months
112
Does pericardiectomy prolong survival in cases of hemangiosarcoma, without removal of the primary neoplasm?
No.
113
What are the most common heart based tumours?
Chemodectoma, ectopic thyroid carcinoma, parathyroid masses.
114
Why are chemodectomas thought to occur more frequently in brachycephalic dogs?
Secondary to overstimulation of the chemoreceptors by hypoxia. Males appear overrepresented.
80% of chemodectomas are located at the aortic body (outer wall of the ascending aorta at the base of the heart).
115
Does pericardiectomy prolong survival in dogs with chemodectoma?
Yes, regardless of age or whether pericardial effusion is present. MST with pericardiectomy is 730 days, without 42 days.
116
What are some indications for pacemaker therapy?
High grade second or third degree AV block, sick sinus syndrome, sinus arrest, chronic bradyarrhythmias.
117
When might surgical rather than transvenous pacemaker placement be preferred?
Small dogs and cats, or with conditions that could cause thromboembolism or bacteremia.
118
What are the two types of pacemakers available?
1. Unipolar: lead tip serves as the cathode and the metal case of the pulse generator serves as the anode.
2. Bipolar: the leads have two electrodes (anode and cathode) at the end, completing a shorter circuit. This prevents skeletal muscle stimulation and there is less potential for electromagnetic interference.
There are also two methods of fixation:
1) Active fixation: screw-type end that penetrates the myocardium.
2) Passive fixation with a button that is sutured in place.
119
What are the available surgical approaches for pacemaker placement?
Fifth or sixth left lateral thoracotomy, or midline celiotomy that extends cranially over the xiphoid.
120
What are some complications associated with epicardial pacemaker placement?
Complications occur in 25% of dogs (compared to 8% for intravenous pacemaker placement).
Hemorrhage during lead placement, postoperative skeletal muscle twitching, lead dislodgment, refractory ventricular fibrillation, pacemaker generator failure from loose set screws, and infection around the generator.
121
What is the MST for dogs undergoing epicardial pacemaker placement?
32 months
