40 – Heart Transplantation




40 Heart Transplantation


Stephen J Pettit and Anna Kydd



Introduction


Heart transplantation remains the definitive treatment for advanced heart failure that is refractory to conventional medical and surgical therapy. Over 110,000 heart transplants have been performed worldwide. Survival is excellent with a median survival of 11 years for all patients and 13 years for patients that survive the first year. The majority of patients return to a normal quality of life. Heart transplantation is limited by supply of suitable donor hearts. For this reason, the waiting time for heart transplantation is long and many patients deteriorate while waiting. Selected patients receive mechanical circulatory support with implantable or paracorporeal ventricular assist devices as a bridge to heart transplantation. These patients pose a particular challenge when they come to heart transplantation, but their outcomes need not be adversely affected.


The time of greatest risk for mortality after heart transplantation is during the immediate postoperative period when patients are on the critical care unit. It is important that cardiac surgeons, cardiologists and intensive care doctors share an awareness of the goals of treatment and common problems in order to deliver excellent outcomes. Greater institutional experience is associated with a lower incidence of complications and higher survival after heart transplantation. This is vital for the success of a transplant programme because outcomes are closely scrutinised by regulatory bodies.



Preoperative Assessment


Patients are assessed by a multidisciplinary team before acceptance onto a waiting list for heart transplantation. Assessment serves several purposes. The team must determine whether the patient is expected to derive symptomatic and prognostic benefit from heart transplantation. The team must identify any contraindications to heart transplantation; common problems that may preclude heart transplantation are listed in Table 40.1. Finally, the team must enable the patient to make an informed decision about whether they wish to be placed on the waiting list for heart transplantation. Intensive care doctors are important members of the multidisciplinary team. Problems with airway management, vascular access, ventilatory support, nutritional support and psychological difficulties may be predictable in certain patients. Postoperative critical care planning should begin at the time of preoperative assessment.




Table 40.1 Common absolute and relative contraindications to heart transplantation




























Absolute contraindications Relative contraindications
Transpulmonary pressure gradient >15 mmHg Advanced age
Pulmonary vascular resistance >5 Wood units Body mass index >32 or <17.5
Irreversible renal dysfunction Recent pulmonary embolism
Sepsis or active infection Smoking, alcohol or substance misuse
Microvascular complications of diabetes Severe mental health disorder
Malignancy within 5 years (except skin)


Transfer from the Operating Room


It is important to understand any problems that were encountered in the operating room at the point of admission to the critical care unit. An early indication of allograft function will be given by visual inspection of the donor heart as cardiopulmonary bypass is weaned, the amount of cardiovascular support required, invasive haemodynamic data (cardiac index, pulmonary capillary wedge pressure and right atrial pressure) and blood tests including mixed venous oxygen saturation and serum lactate. In the most severe forms of primary graft dysfunction, patients may leave the operating room with venoarterial extracorporeal membrane oxygenation (VA ECMO) support. The team in the critical care unit should receive the patient and ensure that they are in a satisfactory haemodynamic state. Any immediate surgical problems should be identified before the operating room team stand down.



Postoperative Care


Excellent long-term outcomes after heart transplantation are dependent on excellent postoperative care in the critical care unit. Patients change rapidly in the immediate postoperative period. Close observation by all members of the multidisciplinary team is vital. Treatment will need to be continually adjusted on an individual patient basis. The basic principles of care are outlined in Table 40.2.




Table 40.2 Principles of care after heart transplantation













Support allograft function
Allow recovery of end-organ function
Establish immunosuppression
Avoid infection

A series of investigations are routinely performed to assess allograft function and look for common problems. These include regular blood gas analysis, daily venous blood tests, an electrocardiogram, chest radiography and transthoracic echocardiography. Additional investigations such as cross-sectional imaging and therapeutic drug monitoring assays are arranged if needed. Surveillance endomyocardial biopsy is usually performed on a weekly basis during the first month after heart transplantation, but this is generally deferred until the patient is discharged from the intensive care unit unless there is specific concern about acute rejection. Common problems after heart transplantation are summarised in Table 40.3.




Table 40.3 Common problems after heart transplantation

















Right ventricular dysfunction
Acute kidney injury
Bleeding into pericardial or pleural space
Sinus node dysfunction or high grade AV block
Atrial arrhythmias
Systemic inflammatory response syndrome


Airway and Ventilation


All patients will be sedated and mechanically ventilated via an endotracheal tube until they are ready for extubation. Many sedative drugs cause vasodilatation and drive use of potentially deleterious vasopressors. Mechanical ventilation must be used with care. Excessive tidal volume and positive end-expiratory pressure (PEEP) should be avoided. Both increase right atrial pressure, worsen tricuspid regurgitation and increase right ventricular work by increasing pulmonary vascular resistance. Hypoxia should not be permitted because it will cause pulmonary vasoconstriction, increase pulmonary vascular resistance and increase right ventricular work. Inhaled therapies such as nitric oxide and iloprost may be used to reduce pulmonary vascular resistance in selected patients.



Cardiovascular


Sinus node dysfunction and atrioventricular (AV) block are common after heart transplantation. All patients should leave the operating room with temporary epicardial pacing wires. It is important to ensure that these are attached to a temporary pulse generator and that the pacing system is working correctly. Sinus tachycardia should be expected in the denervated heart. However, this is not always present in the immediate post transplant period. Demand pacing in a dual chamber mode (DDD) with a lower rate limit of 90–100 beats per minute is routine. A relatively high heart rate may improve cardiac output in a transplanted heart when the ability to augment stroke volume is limited. Pacing threshold, sensing and underlying rhythm should be assessed on a daily basis. Sinus rhythm and AV conduction typically return within 1 to 3 weeks of transplantation but around 10% of patients will require a permanent pacemaker.


All patients require continuous invasive monitoring of cardiovascular performance in the immediate postoperative period. This is most commonly achieved with a pulmonary artery catheter. It is helpful to establish desirable haemodynamic ranges; an example is provided in Table 40.4. Measurements outside the desirable range should prompt review and exclusion of a surgical problem such as haemopericardium or haemothorax. In the absence of a surgical problem, abnormal haemodynamics may represent a target for treatment. Abnormalities such as hypovolaemia may be easy to identify and treat. It is important to recognise that right ventricular dysfunction is common after heart transplantation and a leading cause of primary graft failure. Risk factors for right ventricular dysfunction include older donor age, longer ischaemic time, low donor height/weight relative to recipient and high pulmonary vascular resistance in recipient. Right ventricular dysfunction is normally identified by a low cardiac index and rising right atrial pressure. Treatment of right ventricular dysfunction is complex and the principles are outlined in Figure 40.1. It is vital that high right atrial pressure is not permitted because this will lead to right ventricular distension and a downward spiral of right heart failure.




Table 40.4 Desirable haemodynamic parameters after heart transplantation

























Haemodynamic parameter Desirable range
Mean arterial pressure 70–90 mmHg
Mean right atrial pressure 5–12 mmHg
Mean pulmonary capillary wedge pressure 5–12 mmHg
Cardiac index >2
Mixed venous oxygen saturation >70%




Figure 40.1 Treatment of right ventricular dysfunction. CVVH continuous venovenous haemofiltration.


Use of inotropic or vasoactive medications in isolation or combination after heart transplantation is common but there is no good evidence base to support the superiority of any particular regime. Agents should be selected according to individual patient physiology and the desired effect. The expected effects in a typical patient are outlined in Table 40.5. In general, the dose of inotropic or vasoactive medications should be minimised and the medications should be progressively weaned as recovery of allograft and end-organ function is seen. Intra-aortic balloon pump (IABP) counterpulsation will increase coronary blood flow and reduce left atrial pressure, both of which may be helpful in right ventricular dysfunction.




Table 40.5 Expected effects of agents used for cardiovascular support after heart transplantation












































Agent Contractility SVR PVR
Adrenaline Increased Increased Neutral
Noradrenaline Increased Increased Increased
Dopamine Increased Increased Neutral
Arginine vasopressin Neutral Increased Increased
Type 2 PDEi Increased Decreased Decreased
Hydralazine Neutral Decreased Neutral

Mechanical circulatory support may be required when inotropic, vasopressor/vasodilator and intra-aortic balloon pump support is insufficient to achieve desired haemodynamic parameters. Percutaneous devices to mechanically support the right ventricle are now available but have not been widely used after heart transplantation. VA ECMO is thought to be the best treatment for severe primary graft failure. Central cannulation may be preferable to peripheral cannulation to allow longer support duration, permit left ventricular venting and reduce the risk of peripheral vascular complications. Primary graft dysfunction may improve sufficiently for VA ECMO to be weaned in up to 90% of patients within 1 week. In the most severe cases, central VA ECMO may be used as a bridge to acute re-transplantation.

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Jan 9, 2021 | Posted by in CARDIOLOGY | Comments Off on 40 – Heart Transplantation
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