Cardiothoracic Surgery Flashcards
Primary vessels affected by atherosclerosis
- Proximal LAD
- Circumflex
- Right coronary
Outline the pathological process of atherosclerosis
- Endothelial injury due to risk factors
- LDL accumulation leads to intimal thickening and atheroma formation
- Platelet adhesion causes microthrombi and release of platelet-derived growth factor
- Monocytes/macrophages engulf cholesterol to become foam cells
- Further LDL is taken up by macrophages causing release of IL-1 and TNF which stimulates smooth muscle and fibroblast proliferation
- Fibroblasts lay down collagen/elastin to mature the plaque
- Chronic inflammatory process leads to calcification
What is the role of platelet-derived growth factor in atherosclerosis
- Released from endothelial cells
- Attracts monocytes to area which engulf cholesterol to become foam cells
How are foam cells formed
From monocytes and macrophages engulfing cholesterol
What happens to the smooth muscle cells in atherosclerosis
Migrate from the media to the intima and transform into secretory cells producing collagen, elastin, chemokines
Symptoms associated with varying degrees of stenosis
- 50% = asymptomatic
- 75% = exertional angina
- 90% = angina at rest
Invasive management of stable angina
- PCI if symptoms difficult to control with medical therapy
2. CABG if anatomy unsuitable for PCI
Invasive management of unstable angina
- PCI if anticoagulation and nitrates unsuccessful
2. CABG if PCI unsafe
Invasive management of myocardial infarction
- PCI 1st line
2. CABG rarely used
Advantages of PCI
- Minimally invasive
- Low morbidity
- Low immediate complication rate
Disadvantages of PCI
- Unsuitable for left main stem lesions
- Early re-occlusion and stent thrombosis
- High rate of symptom recurrence
- Poorer ‘freedom’ from medication
- Requires cardiac surgical back up
Advantages of CABG
- Reliable revascularisation
- Suitable for a wide range of coronary lesions
- Ability to perform simultaneous procedures e.g. valve replacement
Disadvantages of CABG
- Major procedure
- Morbidity from sternotomy and conduit harvesting sites
- Late graft failure (especially if saphenous vein used)
What investigation must be performed prior to cardiac surgery
Coronary angiography (for those undergoing CABG and those with risk factors undergoing valve replacement who would benefit from revascularisation at the same time)
Characteristics of Fibrolipid plaques (structure and location within the vessel wall)
- Lipid-rich core
- Overlying fibrous cap on the luminal surface
- Tends to spare arteries of the upper limb
- Between intima and lamina
Outline the 3 microscopic components of atherosclerotic plaques (cells, connective tissues, lipids)
- Cells = mainly vascular smooth muscle cells, macrophages, lymphocytes
- Connective tissue fibres = collagen, elastin, proteoglycans
- Lipids = mainly cholesterol and oxidised cholesterol in the form of LDLs
List the risk factors for developing atherosclerosis
- Increasing age
- Male sex
- Race
- Smoking
- DM
- Obesity
- HTN
- Hyperlipidaemia
- Family history
How many units of blood should be cross-matched prior to cardiac surgery
4 units
Which medications should be stopped 7 days prior to cardiac surgery
- Platelet antagonists (clopi 5 days prior)
- ACE-i due to risk of severe perioperative vasodilatation
What is the role of TOE in cardiac surgery
- Evaluates cardiac wall and valve function
- Checks for air bubbles after closure
Patient position for median sternotomy
Supine
Skin prep prior to cardiac surgery
- Prep chest and both groins in case an intra-aortic balloon pump of femoral bypass is required
- Both arms and legs if harvesting planed
Median sternotomy provides good access to
- Epicardial coronary arteries
- Ascending aorta
- Aortic valve
- Mitral valve
What ligament lies at the top of the midline sternotomy incision
Interclavicular ligaments
Describe the median sternotomy incision
2cm below the sternal notch to the xiphoid, deepen through the fat with diathermy
What drains may be used at closure of the thorax
Under-water drains:
- Pericardium
- Left and right pleurae
Immediate complications of midline sternotomy
Vessel (e.g. brachiocephalic) or chamber (e.g. right ventricle) injury
Late complications of midline sternotomy
- Sternal dehiscence
- Sternal osteomyelitis
- Wire sinuses
How is cardioplegia achieved in CPB
Delivers cold blood with high potassium content to arrest the heart
Indications for CABG
- Left main stem stenosis or equivalent (proximal LAD, circumflex)
- Triple vessel disease
- Diffuse disease unsuitable fo PCI
What are the physiological conditions created by CPB
- Non-pulsatile flow with mean perfusion pressure of 60mmHg
- Systemic cooling at 30-32 degrees
Why is de-airing performed and where is it usually done
- To prevent air entering the circulation and causing CVA
- Aortic root or LV apex
List the complications of CPB
- Coagulopathy from platelet dysfunction
- Inflammatory activation and vasodilation
- CVA
- Bleeding
- Cardiogenic shock
- Cognitive performance impairment
What are the indications for an intra-aortic balloon pump
- Pre-op for poor cardiac output or critical coronary stenosis
- Post-op when more haemodynamic compromise is seen or anticipated
How is an intra-aortic balloon pump inserted
Via the femoral artery in the groin and placed in the descending aorta
Function of intra-aortic balloon pump
- Reduces afterload and therefore myocardial work
- Inflates during diastole to augment maximal diastolic pressure to improve coronary perfusion
What is involved in a standard triple bypass CABG
- Left internal mammary to the LAD
- Portion of long saphenous to the circumflex
- Portion of long saphenous to the distal right coronary
Surface anatomy of the long saphenous vein
- Ankle - vein immediately anterior to medial malleolus
- Knee - one hand breadth posterior to medial patellar border
- Groin - 1cm medial to midinguinal point
What nerve must you be wary of when harvesting the LIMA
Phrenic nerve as it crosses IMA at 1st rib
Why are radial artery grafts becoming more popular as opposed to saphenous grafts
Due to the risk of late occlusion with saphenous grafts
What test must be performed prior to radial artery harvesting
Allen’s test to ensure adequate ulnar blood flow
What group of people are excluded from radial grafting
Those with high functional requirements of the hands
List the immediate complications of CABG
- Bleeding
- Low cardiac output syndrome
- MI
- Neurological complications
List the early complications of CABG
- Pneumonia
- Sternal infections
- Leg infections
- Renal failure
- Atrial dysrhythmias
- UGIB and perforation
Late complications of CABG
Recurrent stenosis
How is low cardiac output syndrome managed
- Maintenance of sinus rhythm (medically or paced)
- Optimise preload/afterload (e.g. use Swan-Ganz)
- Maintain HCT >30%
- Inotropes
- Vasodilators to reduce afterload
- Intra-aortic balloon pump
What nerves must you be wary of when harvesting the radial artery
- Superficial radial nerve
- Lateral antebrachial cutaneous nerve
What nerve must you be wary of when harvesting the long saphenous vein
Saphenous nerve (will cause sensory loss over front and medial leg)
Signs and symptoms of sternal infection
- Sternal click on moving
- Pain
- Sternal instability
- Discharge/wound breakdown
- Movement of wires on CXR
Long term complications of cardiac angioplasty
Restenosis
Long term complications of cardiac stenting
Stent thrombosis
Criteria for severe aortic stenosis
- Aortic area <1cm^2
- Jet velocity >4ms
- Transvalvular pressure >40mmHg
Risk factors for calcific aortic stenosis
- Age
- Bicuspid valve
- Rheumatic fever
- Hypercalcaemia
- Congenital bicuspid valve
What type of bacteria causes rheumatic fever
Group A beta-heamolytic streptococcus
What occurs to the aortic valve in rheumatic fever
Fibrosis of the valve with fusion of the commisures
How is the risk of endocarditis reduced pre-operatively
- Dental examination
- Chest examination
- Urinalysis
- Temperature check
Mechanical Vs Bioprosthesis - who receives which
- Young active people without major comorbidity should receive a mechanical valve
- Elderly patients should receive bioprosthesis
What are the two approaches to TAVI
- Retrograde transfemoral or subclavian approach
2. Antegrade transapical approach (via left anterolateral mini-thoracotomy)
How does aortic regurgitation typically present
Pulmonary venous HTN
Causes of aortic regurgitation
- Rheumatic disease
- Annuloaortic ectasia (associated with Marfans)
- Endocarditis
- Large-vessel vasculitis
- Acute ‘Type A’ dissection