Mitral Valve Replacement Flashcards
1
Q
A 45-year-old female patient is listed for mitral valve replacement due to
severe mitral valve stenosis.
What is the normal area of the mitral valve?
A
- The normal mitral valve area is more than 4 cm2.
- Mitral stenosis is a valve area of <2 cm2, with severe stenosis <1 cm2.
2
Q
What are the common causes of mitral stenosis?
A
- Rheumatic heart disease secondary to rheumatic fever (most common cause worldwide).
- Degenerative calcifcation.
- Infective endocarditis.
- Congenital (uncommon).
- Infiltrative diseases: sarcoidosis/amyloidosis (rare).
3
Q
What common symptoms might you expect in this patient?
A
- Fatigue.
- Dyspnoea.
- Reduced exercise tolerance.
- Cough.
- Palpitations (if presence of atrial fibrillation).
- Increased frequency of respiratory tract infections.
4
Q
How is mitral stenosis classified?
A
- Mitral stenosis is classified based on the valve area and the mean pressures across the valve found on echo:
- Mild: 1.6–2.0 cm2, pressure <5 mmHg.
- Moderate: 1.5–1.0 cm2, pressure 6–10 mmHg.
- Severe: less than 1.0 cm2, pressure >10 mmHg.
5
Q
Why is atrial fibrillation more common in patients with mitral stenosis?
A
- Patients with severe mitral valve stenosis develop increased left atrial pressure, due to the impedance to left ventricular filling from a progressively narrowed mitral valve.
- A high left atrial pressure causes increased stretching and dilation of the left atrium, increasing the likelihood of atrial dysrhythmias such as atrial fibrillation.
- These patients should be anti-coagulated owing to the higher likelihood of thrombotic events.
6
Q
What are the concerns when assessing this patient preoperatively?
A
- Implications of severe mitral valve stenosis: focus on signs, symptoms, and investigations that evaluate the severity of the pathophysiological process and degree of impairment of physiological reserve, including evidence of dysrhythmias, pulmonary venous congestion and pulmonary oedema, pulmonary hypertension, and right heart failure.
- She is a high-risk patient requiring preoperative assessment and anaesthesia managed by a cardiac anaesthetist, following preoperative optimisation with medical therapy.
- If the patient is on warfarin for atrial fibrillation, consider bridging therapy with an intravenous heparin infusion.
- Evaluate any comorbidities, including the cause of her cardiac disease and evidence of other end-organ dysfunction.
- Take a routine anaesthetic history and conduct an airway assessment, including her past medical and social history, and any allergies.
7
Q
What are the anaesthetic goals for this patient?
A
1) Preserve left ventricular preload:
- Low-normal heart rate – to preserve diastolic left ventricular filling and left ventricular end-diastolic volume, which serves to optimise left ventricular preload.
- Sinus rhythm – atrial fibrillation, with absence of atrial contraction, will detrimentally reduce left ventricular end-diastolic volume.
- Judicious use of fluids, in order to maintain preload while avoiding worsening pulmonary oedema.
2) Maintain contractility:
- Avoid myocardial depressants. In the presence of right ventricular failure, inotropic support with right ventricular afterload reduction strategies may be required.
3) Optimise afterload:
- Preservation of normal left ventricular afterload. As left ventricular cardiac output is relatively fixed, both a high or low afterload will be poorly tolerated.
4) Avoid worsening pulmonary hypertension or right ventricular aferload
* Avoid hypoxia, hypercarbia or acidosis, which would detrimentally increase pulmonary arterial resistance and right ventricular afterload. This includes adequate pain control in the peri-operative period.
8
Q
After surgical mitral valve implantation, the patient is to be weaned from cardiopulmonary bypass. How would you prepare for this?
A
- Re-warm the patient as guided by core and peripheral temperature monitoring. Avoid hypo and hyperthermia.
- De-airing: The heart needs to be de-aired, as directed by the surgical team. TOE is useful to search for any residual air.
- Adequate lung ventilation: If possible, visually check the surgical field for optimal lung re-expansion. Ventilate with 100% oxygen. Consider suctioning the endotracheal tube for secretions.
- Re-establish an appropriate heart rhythm and rate and ensure pacing equipment provides electro-mechanical capture. Aim for a heart rate of 80–100 and sinus rhythm. Epicardial pacing may be necessary to achieve this and to optimise sequential atrio-ventricular contraction.
- ST segment monitoring: Evidence of ischaemia should raise concern. Consider coronary air, graft or coronary occlusion, or an insufficient coronary perfusion pressure.
9
Q
After surgical mitral valve implantation, the patient is to be weaned from cardiopulmonary bypass. How would you prepare for this…..continued?
A
- Vasoactive medication: Consider the need for inotropes, vasopressors and arteriolar or veno-dilators as appropriate. In this case:
- Consider inotropic support: Evaluate the patient’s baseline ventricular function, the potentially deleterious effects of CPB, and the anticipated physiological effects of replacing the valve in the context of the pathology. Thus, consider the need to support left ventricular dysfunction, particularly if there is evidence of chronic deconditioning. Also consider the need to support the right ventricle if there is evidence of congestive heart failure.
- Consider vasopressor support e.g. to maintain coronary perfusion pressure in the presence of vasodilation from a SIRS response to CPB.
- Acid–base balance: Correct metabolic acidosis if present.
- Electrolytes: Normalise electrolytes (Na+, K+ and Ca2+) aiming for
high-normal potassium. - Blood sugar: Avoid hypo or hyperglycaemia.
- Haemoglobin: Optimise the haematocrit with blood products where
necessary.
10
Q
Following her mitral valve replacement, this patient is transferred to cardiac intensive care postoperatively. She remains intubated and ventilated. 6 hours later her blood pressure drops to 74/42 and her heart rate is 120. Her CVP rises from 12 to 18.
What is the definition of cardiac tamponade?
A
- Cardiac tamponade occurs when there is an accumulation of fluid in the pericardial sac to an extent that it creates an increased pressure within the pericardial space, thereby inhibiting effective filling of the heart chambers. This leads to a reduction in cardiac output and causes haemodynamic compromise and obstructive shock.
- A blood clot in the pericardial space causing external compression of the heart can also produce tamponade physiology.
- It can lead to life-threatening end-organ dysfunction, cardiovascular collapse and cardiac arrest.
11
Q
A bedside echocardiogram demonstrates the presence of blood in the pericardium. What is your immediate management of this patient?
A
- The findings suggest that the patient has developed cardiac tamponade postoperatively.
- This is an unstable patient that requires immediate evacuation of blood from the pericardial space.
- Call for urgent senior anaesthetic help and carry out a rapid assessment of the patient.
- Activate the cardiac unit’s emergency team – this should include a cardiothoracic surgeon, the theatre team, and potentially a perfusionist.
12
Q
A bedside echocardiogram demonstrates the presence of blood in the pericardium. What is your immediate management of this patient?
Aims?
A
- Aim to optimise haemodynamics:
- Administer fluid boluses to increase ventricular filling pressure to
counteract the diastolic filling restriction and improve ventricular preload. - Avoid high PEEP or high airway pressures, which would further
compromise ventricular filling. - Consider vasoactive medication. While inotropes may increase
cardiac output, they also may increase myocardial oxygen demand. Vasopressors may help to improve coronary and systemic perfusion but high afterload is poorly tolerated. - While the above may form temporary haemodynamic stability, the definitive treatment is to relieve the tamponade. For a postoperative cardiac patient: re-sternotomy, relief of the tamponade, and exploration for a possible bleeding source and surgical haemostasis should be emergently considered.
- Note that this patient may have a degree of coagulopathy post cardiac surgery, which should be considered and corrected if present.
13
Q
As you approach the patient, she arrests. You note that the rhythm on the monitor is ventricular fibrillation. How do you proceed?
A
- Follow the Cardiac Advanced Life Support algorithm.
- This is a witnessed cardiac arrest with a recognisable rhythm in a patient who has just undergone cardiac surgery. Under these circumstances, external chest compressions may be delayed by 1 minute to facilitate the timely administration of three sequential shocks (for ventricular fibrillation or pulseless ventricular tachycardia). Therefore, administer three successive shocks (at 150J) and then commence external chest compressions.
14
Q
As you approach the patient, she arrests. You note that the rhythm on the monitor is ventricular fibrillation. How do you proceed……continued?
A
- Administer 300mg IV amiodarone and prepare for an emergency re-sternotomy.
- Continue CPR with a single defibrillation attempt every 2 minutes.
- Re-sternotomy should occur within 5 minutes of cardiac arrest. This will facilitate internal cardiac massage, defibrillation (20 J) and release
of tamponade. - Continue ventilation with 100% oxygen and switch of PEEP. Confirm the position of the endotracheal tube and auscultate to ensure bilateral air entry.
- Avoid adrenaline unless specifically directed by a senior clinician, given the potential for profound hypertension after ROSC and thus the potentially catastrophic effect of damage to, and bleeding from, surgical anastomoses or suture lines.
15
Q
MVR important bits
A
- arrhythmias
- LV and RV failure, pHTN
- causes, dimensions
- intra-op goals (maintain preload, afterload, contractility, NSR, avoid triggers of pHTN/RV afterload)
- CPBP weaning
- Cardiac tamponade mx
