Valvular Disease

The incidence and types of valvular disease have changed over the past 50 years.¹ Valvular disorders, such as mitral stenosis and aortic regurgitation, often arise from infectious diseases like rheumatic fever and syphilis, which are much less common today. Conversely, there has been a rise in the rate of aortic stenosis, which is due to degenerative disease common in ageing. In contrast to these trends, the prevalence of rheumatic fever and rheumatic heart disease among Indigenous Australians is one of the highest in the world.² Also, Pacific Islanders living in New Zealand have much higher rates of rheumatic fever than the general population.³ As a result, valvular disorders are much more common in these groups. Rheumatic fever is discussed under infective endocarditis in Chapter 10.

Stenotic valves have a tightened, restricted orifice, so that blood must be forced through at higher pressure (Figure 12.1). In regurgitation, also called valvular incompetence or insufficiency, incomplete closure of the valve leaflets results in backflow of blood. Valvular conditions can result from congenital deformities, but also from the degenerative changes associated with ageing, from infection and rheumatic diseases. When a valve is stenosed, higher pressure is required to push blood through the narrow opening and the heart compensates by hypertrophy and dilation. When a valve is incompetent the heart does not empty sufficiently, so again the heart compensates by hypertrophy and dilation. In both these conditions heart failure may result; however, in regurgitation, pressure in the ventricles and atrium grows and this pressure is reflected back into the pulmonary or venous system. Although the heart contains four valves, the majority of disorders affect the mitral and aortic valves in the left side of the heart.

FIGURE 12.1 Valvular stenosis and regurgitation: (A) normal position of valve leaflets (cusps) when the valve is open and closed; (B) open position of a stenosed valve (left) and closed position of a regurgitant valve (right); (C) haemodynamic effect of mitral stenosis shows the mitral valve is unable to open completely during left atrial systole, limiting left ventricular filling; (D) haemodynamic effect of mitral regurgitation shows the mitral valve does not close completely during left ventricular systole, allowing blood to re-enter the left atrium.⁴³

Ischaemic Heart Disease

The pathophysiology and implications of ischaemic heart disease are explained in detail in Chapter 10. Single lesions can be treated by angioplasty and stent; however, multiple, longer lesions may need coronary artery bypass surgery.⁵

Coronary Artery Bypass Graft Surgery

CABG uses a section of vein or artery to bypass a blockage in the patient’s coronary artery. The vessels used for grafting arise from the internal mammary artery, or are taken from the saphenous vein or radial artery. Saphenous veins are removed from the legs, and the radial artery from the forearm and used as a free graft with anastomoses at the ascending aorta and distally to one or more coronary arteries. When saphenous veins are used as grafts (SVG), they often develop diffuse intimal hyperplasia, which ultimately contributes to restenosis. Patency rates are lowest in saphenous vein grafts attached to small coronary arteries or coronary arteries supplying myocardial scars. Consequently, arterial grafts are used more often, as they are more resistant to intimal hyperplasia. Internal mammary arteries (IMAs) and radial artery grafts may be used.⁶ The IMA remains attached to the subclavian artery and is mobilised from the chest wall and anastomosed to the coronary artery distal to the occlusion (Figure 12.2). If the radial artery is being harvested for grafting, the collateral circulation in the forearm is assessed. Echo colour Doppler provides best accuracy of forearm circulation, although the clinical Allen test is quite commonly used. The disadvantage of the Allen test is that it has around 5% false patency result.⁷ A selection of IMA, SVG and radial artery grafts may be necessary over time as repeat procedures are needed or in patients with extensive disease requiring multiple grafts.

FIGURE 12.2 Internal mammary artery graft⁵.

Over recent years a new approach to CABG – minimally invasive direct coronary artery bypass grafting (MIDCABG) – has been used. This procedure uses intercostal incisions and a thorascope instead of a sternotomy to access the heart and coronary arteries. MIDCABG is also often performed without cardiopulmonary bypass (off pump coronary artery bypass, OPCAB); instead, the heart is slowed with beta-blockers to allow the surgery to be performed on a beating heart.⁸ OPCAB procedures may also be performed using full or partial sternotomy to provide access for multiple vessels grafting. Both procedures have been successful responses to the drive to reduce recovery times, patient stays in hospital and costs.⁸ MIDCABG is currently only used in single-vessel disease, particularly the left anterior descending (LAD) artery. More recently, robotically-assisted cardiac surgery has been performed in America and Europe and has been introduced at a small number of Australian hospitals for CABG and mitral valve surgery. This technique has further reduced the invasiveness of cardiac surgery, as little more than stab wounds are required in the right chest for thoroscopy and the robotic instruments. Avoiding true thoracotomy or sternotomy improves postoperative pain experiences and shortens length of stay.⁹

Although CABG is the most common cardiac surgical procedure undertaken in Australia, the incidence has declined since 2005/06 to be 61 procedures/100,000 population in 2007–08.¹⁰ The decline in surgery rates is due to changes in the treatment of CHD, including the advent of percutaneous coronary intervention (PCI). More procedures are now being performed in older patients, with 73% of current patients aged over 60 years.¹ CABG is used to relieve the symptoms of angina by increasing coronary blood flow distal to occlusive coronary lesions. It is a palliative, not curative, treatment as the underlying disease process continues.¹¹ CABG is more effective than PTCA in patients with extensive, multi-vessel disease.^9,11 CABG is also used in left main vessel lesions due to the high risk of extensive infarction associated with PTCA in this area. Women do not appear to have the same access to CABG surgery, as men are three times more likely to have surgery, although only twice as likely as women to have CHD.¹² CABG surgery is commonplace, and many cardiothoracic centres have highly efficient, effective systems in place with mortality rates as low as 2%.

Valve Repair and Replacement

Valve surgery is usually undertaken to repair the patient’s valve or, more often, to replace the valve with either a mechanical or tissue prosthesis. The clinical decision for valve surgery is primarily based on the clinical state of the patient using the New York Heart Association (NYHA) classification system and echocardiographic findings.⁵ The type of surgery used will depend on the valves involved, the valvular pathology, the severity of the condition and the patient’s clinical condition. Often valve surgery is not a single procedure, and it may involve multiple valves, CABG and implantable cardioverter defribillator (ICD). Valve surgery is palliative, not curative, and patients will require lifelong health care.

Valve repair may involve resecting and/or suturing prolapsed or torn leaflets (valvuloplasty) and repairing the ring of collagen the valve sits in (annuloplasty), and is commonly used for mitral and tricuspid regurgitation. Commissurotomy (incising valve leaflets and debriding calcification) is the treatment of choice for mitral stenosis. Both repair processes have demonstrated lower operative mortality than replacement, although complete valve competence may not be able to be achieved. Open procedures are preferred because thrombi and calcification can thereby be removed.

Valve replacement may be necessary, but could be associated with higher risks due to long-term disease process and poor underlying left ventricular function. The most common indication for valve replacement is aortic stenosis, and accounts for 60–70% of valve surgery.¹³ Prosthetic valves may be mechanical or biological. Mechanical valves are made of metal alloys, pyrolite carbon and Dacron (Figure 12.3). Biological valves are constructed from porcine, bovine or human cardiac tissue. Mechanical valves are more durable but have an increased risk of thromboembolism, so lifelong anticoagulation is required. Biological valves suffer from the same problems as the patient’s valve (i.e. calcification and degeneration). The choice of valve depends on the age of the patient and potential difficulties with taking anticoagulants.

FIGURE 12.3 Prosthetic valves: (A) the Bjork-Shiley valve, with a pyrolyte-carbon disc that opens to 60 degrees; (B) the Starr-Edwards caged-ball valve model 6320, with satellite ball; (C) the St Jude Medical mechanical heart valve, with a mechano-central flow disc; (D) the Hancock II porcine aortic valve, with stent and sewing ring covered in Dacron cloth.⁵

Mortality for valvular surgery is higher than for CABG, reflecting the underlying loss of ventricular function and additional procedures that are common. Risk stratification models have been developed to help determine the patients that are most likely to have poor recovery and outcomes.¹⁴ The major factors that contribute to poor outcomes are worse left ventricular function and age over 70 years old.

Cardiopulmonary Bypass

CPB was developed to enable surgery to be performed on a still, relatively-bloodless heart, while preserving the patient’s circulation. CPB temporarily performs the functions of the heart in circulating blood and of the lungs by enabling gas exchange with the blood. Silicone cannulae are inserted into the venae cavae and venous blood circulated through a circuit outside the body. In this circuit the blood is oxygenated, carbon dioxide removed and blood temperature controlled. Drugs and anaesthetics may be added. A roller pump is generally used to provide the pressure to create blood flow in the circuit and back to the patient’s aorta.

Adverse effects of CPB are diverse, and include the following:¹⁵

These effects are well documented, and routine CPB management and postoperative care are designed to minimise and treat the complications. Heparin is added at the commencement of CPB and is reversed with protamine (1 mg of protamine for every 100 units of heparin) when CPB ceases; activated clotting times are monitored throughout and after CPB. Blood returning to circulation is filtered, and surgical procedures proceed carefully to reduce microemboli. Monitoring and maintenance of adequate arterial flow rates are used to prevent low perfusion. Temperature gradients and a rewarming process are instituted slowly so that cardiac output can meet metabolic demands.

Myocardial Preservation

One of the processes involved in CPB is that the aorta is clamped where a cannula is inserted to return blood to the circulation. This clamp prevents blood flow into the coronary arteries; therefore, the myocardium must be protected from ischaemia. This protection is achieved through several mechanisms directed towards reducing oxygen demand: first, oxygen demand is reduced by mild to moderate hypothermia (28–32°C); second, by reducing myocardial temperature (0–4°C), through infusing cold fluids directly into the coronary arteries; and third, by preventing normal conduction by arresting the heart during diastole, through infusing a concentrated potassium solution into the coronary arteries. Return to normal rhythm is usually achieved by circulation of warm blood, though defibrillation may be necessary.

The Immediate Postoperative Period

Patients should be transported to intensive care accompanied by at least an anaesthetist, an appropriately qualified nurse and transport personnel under continuous cardiac monitoring and assisted ventilation. It is prudent to include capnography during patient transport to detect ventilator disconnection, dysfunction, or endotracheal tube migration. Intensive care or theatre nursing staff may be a component of the transport team. The admission to intensive care requires a team approach, with the participation of intensive care nursing and medical staff and/or technician input. The immediate postoperative decision making on patient management is influenced by handover from anaesthetists, settling in procedures and collegial assistance.¹⁶ Admission activities are commonly divided between nurses, with one nurse taking responsibility for establishing monitoring and haemodynamic assessment and management, and a second nurse managing ventilation and endotracheal tube security, as well as managing chest drains, gastric tube and urinary catheter. If staffing permits, additional nurses may take responsibility for documentation, performing arterial blood gases, 12-lead ECG and providing assistance as required.

The objectives of immediate post operative management of cardiac surgical patients may include:

Haemodynamic Monitoring and Support

Typical haemodynamic monitoring includes an intra-arterial catheter for continuous blood pressure monitoring and arterial blood sampling. Cardiac output and preload measurement are achieved most commonly with either a pulmonary artery or central venous catheter configured for pulse contour cardiac output (PiCCO) monitoring (see Chapter 9).

Preload measures provided by the pulmonary artery catheter include right atrial pressure (RAP) to approximate right ventricular filling, and pulmonary artery pressure (PAP) to approximate right ventricular systole and provide insight into pulmonary vascular resistance and left heart function. The pulmonary capillary wedge pressure (PCWP) is available to approximate left ventricular filling and left heart function. Alternatively, the PiCCO monitoring system represents preload by intrathoracic blood volume index (ITBVI) and global end-diastolic volume index (GEDVI). In addition, the extravascular lung water index (EVLWI) can demonstrate the accumulation of interstitial lung water.¹⁷

Cardiac output is measured by either intermittent or continuous thermodilution via pulmonary artery catheters, or measured intermittently and then approxi-mated continuously on a beat-to-beat interpretation of pulse contour by the PiCCO monitoring system. Cardiac output measurement can be combined with other pressure variables to calculate systemic and pulmonary vascular resistance, stroke volume and measures of ventricular work.

Certain common haemodynamic patterns are seen in the early postoperative phase. These must be detected through thorough monitoring and interpretation of variables, and managed according to specific needs. During the initial two hours of recovery period, 95% of patients will experience haemodynamic instability.¹⁸

Ventilatory Support

Ventilation should be approached according to the general principles described in Chapter 15. As anaesthesia is not typically reversed at the end of the operation, patients are generally admitted apnoeic, and within 1–3 hours return to wakefulness and spontaneous breathing.

Ensuring a secure airway is an initial priority; the following should be undertaken:

There has been a general trend to more rapid ventilatory weaning in recent years, and in some centres ‘fast-track’ cardiac surgical recovery includes extubation at the end of the operation before transfer to a recovery unit for suitable patients. Indices of respiration show no improvement when intubation is maintained for longer compared with early extubation,³⁰ and pooled results from randomised early extubation trials show earlier ICU discharge and shorter lengths of stay (by 1 day) when early extubation is undertaken.³¹

Apart from these fast-track approaches, ventilation is commonly employed for 2–6 hours in the uncomplicated patient. Reasons for continuing ventilation beyond this time frame may include:

For many patients, ventilation is provided purely for initial airway and apnoea protection rather than for treatment of pulmonary deficits. In the absence of pulmonary disease, many centres provide fairly uniform approaches to parameter settings that aim at sustaining ventilation and oxygenation, while limiting traumatic risk to the lungs (see Table 12.1). However, approaches to ventilation will need to be tailored in the presence of operative complications or coexisting lung disease.

TABLE 12.1 Postoperative ventilation settings

Ventilation challenges specific to the postcardiac surgical setting include:

Assessment and Management of Postoperative Bleeding

The harvest sites for radial arteries or saphenous veins are uncommon sources of significant blood loss and are generally easily managed with dressings or compression. Intrathoracic bleeding, however, may be torrential and threaten life. Occasionally surgical bleeding from the aorta, arterial grafts or myomectomy sites may exceed replacement capabilities, and at times patients succumb to overwhelming haemorrhage. Maintenance of drain patency and strict recording of losses and total fluid balance are paramount, and fluid balance assessments over shorter intervals, even every 5–10 minutes, become necessary during active bleeding. Because of the potential rates of bleeding, the cardiac surgical unit must be equipped to institute rapid volume replacement, and have access to adequate blood and blood product stores, blood warmers, and all necessary procoagulant therapies. In addition, dedicated equipment should be available to facilitate emergency resternotomy to control haemorrhage.

One or more chest drains are inserted to remove and monitor blood loss, but the positioning of drains is variable, depending in part on the procedure performed, the surgical route taken, and surgeon preference. Regardless of these considerations there will always be a retrosternal/anterior mediastinal drain, as the sternum is generally the major source of bleeding in the absence of complications. Additional drains may be inserted in the pericardial or pleural spaces. Pericardial drains are more likely to be inserted following aortic valve surgery, while pleural drains become necessary following mammary artery harvesting or when the pleura is opened for any other reason. Pleural drains may be anterior, posterior, or ‘wrap-around’ configurations in which they project over the anterior lung, following the pleural space first from midline, to lateral and then finally the posterior pleural space.

Reportable postoperative blood losses vary, but greater than 100 mL/h, or greater than 400 mL in the first 4 hours, would generally be regarded as excessive and worthy of surgeon notification. Importantly, excessive bleeding does not always represent a surgical defect that reoperation might correct, as there are many contributors to impaired haemostatic capability in the cardiac surgical patient (see below).

Chest drainage should be monitored closely, and while bleeding is active, volumes should be assessed every 5 minutes and patency of drains ensured to avert tamponade. Sudden cessation of drainage should always raise the possibility of the loss of tube patency and risk of tamponade, but tamponade may also occur while drainage continues, as collections and compression may occur at sites isolated from drains, or losses may simply be occurring faster than that able to be removed by patent drains.

Chest drains should also be observed for bubbling, to assess for air leaks originating from either system faults or patient leaks. When bubbling can be attributed to the patient, the patency of tubes becomes additionally important to avert tension pneumothorax, which may accumulate rapidly, even over the course of a few breaths in the ventilated patient.

Blood transfusions are not aimed at restoring haemoglobin to normal levels, and, despite variations in acceptable levels, relative anaemia is almost universally tolerated. Haemoglobin levels are thus not routinely treated unless below 80 g/L, except in the elderly or when there are significant comorbidities.^19,32 From these levels patients return to normal haemoglobin status within 1 month postoperatively.³²

Assessment and Management of Pericardial Tamponade

Postoperative pericardial tamponade results from the accumulation of blood or effusion fluid within the pericardium. An increasing volume within the pericardial space eventually compresses cardiac chambers, impeding venous return and therefore causing low cardiac output and hypotension. Pericardial tamponade is an emergency, and varies in severity from shock to pulseless electrical activity.

Described as one of the extra-cardiac obstructive shocks, pericardial tamponade often resembles cardiogenic shock. The low cardiac output and hypotension result in oliguria, altered mentation, peripheral hypoperfusion and development of lactic acidosis. Compensation includes tachycardia and marked vasoconstriction, elevating the systemic vascular resistance. As in cardiogenic shock, there is usually elevation of the filling pressures (right atrial, pulmonary artery and pulmonary capillary wedge pressures), sometimes with a particularly suggestive merging of the pulmonary artery diastolic, right atrial and pulmonary artery wedge pressures.²³ Additional features that may be present include muffled heart sounds, decreased QRS voltage, electrical alternans, narrowing pulse pressure and pulsus paradoxus, along with features of increasing anxiety and/or dyspnoea in the awake patient.

Echocardiography is the definitive assessment tool to reveal the presence of pericardial collections as well as identifying the impact on relaxation, filling and contraction of each cardiac chamber. The chest X-ray is of limited use and may show little, even with significant pericardial collections.

Importantly, the ‘classic’ or typical haemodynamic profile described above is not uniformly seen in tamponade, and tamponade should never be excluded because the haemodynamic status does not match this profile. This may be because classic tamponade implies uniform compression of the entire heart, which may not be the case with haemorrhagic tamponade. A clot may develop over just one chamber rather than occupying the entire pericardium, and so there may be compromise to only a single chamber rather than the whole heart.^21,23

Assessment and Management of Postoperative Pain

As much an art as a science, pain control in the cardiac surgical patient remains a major challenge and continues to provide uncertainty and opportunities for nursing clinicians and researchers. Principles are similar to those outlined in Chapter 7. Surgical pain, often complicated by pericardial inflammation, results in differing pain types, requiring different approaches.³⁴ These different approaches to pain management must be balanced against the promotion of spontaneous breathing, chest physiotherapy, mobilisation, and participation in education and lifestyle modification programs.

Analgesic options include intravenous, oral or rectal analgesics, antiinflammatories and, less commonly, epidural therapies and nerve blocks. Intravenous opiates and codeine/paracetamol preparations provide the mainstay of postoperative analgesia. When insufficient, or when clinical and electrocardiographic features suggest pericarditis, antiinflammatory agents such as rectal indomethacin are appropriate. The place of IV COX-2 inhibitors such as parecoxib appear uncertain, as analgesic efficacy now must be weighed against emerging data suggesting increased thrombotic complications.³⁵

Fluid and Electrolyte Management

Fluid therapy in the postoperative period is aimed at maintaining blood volume, replacing recorded and insensible losses, and providing adequate preload to sustain haemodynamic status. Isotonic dextrose solutions (5%) or dextrose 4% + saline 0.18% are commonly used at approximately 1.5 L/day as maintenance fluids.¹⁴

Potassium replenishment is generally necessary according to measured serum potassium. Polyuria is usually evident in the early postoperative period due to deliberate haemodilution while on cardiopulmonary bypass. With polyuria comes potassium losses, which must be treated to avert atrial or ventricular ectopy and tachyarrhythmias. Because of these predictable potassium losses, protocols for potassium replacement may be instituted, with standing orders for potassium replacement (e.g. 10 mmol over 1 hour if the serum potassium is <4.5 mmol/L, or 20 mmol over 2 hours if <4.0 mmol/L). Main line hydration infusions may also have added potassium to avoid hypokalaemia. Hypomagnesaemia may also develop due to polyuria, and is likewise proarrhythmic. Supplementation (magnesium chloride) is often used for arrhythmia management postoperatively, but its effectiveness has been questioned in many trials.³⁶

Hyperkalaemia occurs less often but is seen particularly when there is impaired renal function. Additional contributors to a rising potassium level include acidosis, administration of stored blood, haemolysis, inotrope use, and any postoperative use of depolarising muscle relaxants such as suxamethonium.

Emotional Responses and Family Support

The experience of being diagnosed with a cardiac disorder, waiting for surgery, the surgical experience and recovery is an emotional journey for patients and their families. Regardless of low mortality rates, the possibility of death and painful wounds can concern patients. Consequently, patients undergoing cardiac surgery often experience anxiety and depression, which can be distressing for patient and family.^37–39 Women appear to be more vulnerable to these emotions in relation to cardiac surgery than men.⁴⁰ Although it is normal and potentially protective to experience anxiety, higher levels of these emotions can be destructive. Anxiety and depression are predictive of worse postoperative outcomes, including poorer psychosocial adjustment and quality of life, more cardiac symptoms and readmissions.⁴¹ Therefore, it is essential to consider and address anxiety and depression when providing care for cardiac surgical patients.

Preoperative preparation provided by nurses usually incorporates information and support, so that patients and their families are familiar with procedures and can cooperate during recovery.⁴² However, seeing a patient who is successfully recovering from surgery may instil more confidence. Patients who have had their surgery postponed or who have been operated on in an emergency setting may need additional support. For many patients, fast-track procedures, including admission on day of surgery, early extubation and early discharge processes, decrease the discomfort associated with being away from home and surgical costs. For other patients there is too little time to be informed and understand postoperative and post-discharge care. Also, critical pathways for cardiac surgery do not include assessing the patient’s psychological state, so nurses must take care to consider this aspect. Consequently, family members assume an important role in supporting patients and helping them understand recovery requirements. It is vital that family members understand and anticipate a certain amount of anxiety and depression, particularly in the first week post-discharge. Family members may also be distressed by seeing their loved one ill and the unfamiliar ICU environment and equipment, so the additional requirement for them to assess and support the patient may be onerous. Printed information regarding the surgery, recovery and emotions will be useful for the patient and family.