2019a).
Peripheral oedema
Oedema occurs as a result of over-accumulation of fluid within the interstitial spaces, resulting in tissue swelling which can be uncomfortable and sometimes painful. Peripheral oedema is most frequently seen affecting the legs and particularly the ankles and feet, often making it very difficult for the patient to wear their usual footwear. When severe, peripheral oedema can lead to leakage of fluid through the skin (weeping oedema) or this fluid may collect in blisters which can burst, breaching skin integrity and increasing the risk of infection.
The coronary circulation
Since the heart is continually active, the cardiac muscle fibres of the myocardium require a continual supply of highly oxygenated blood, and this is supplied via the coronary arteries (Figure 3.9). These are relatively small blood vessels originating directly from the aorta and located on the outer surface of the heart. The term coronary refers to the collective appearance of these vessels as resembling a crown that encircles the heart (corona is Latin for crown). The smaller coronary arteries are interconnected by tiny bridging channels termed anastomoses. Should a blockage (e.g. a clot or detached piece of fatty plaque) occur, blood can be diverted into these anastomotic (collateral) channels which can expand and widen, ensuring that the myocardium in proximity to the blockage remains perfused. The anastomotic nature of the coronary circulation allows small blockages to be effectively bypassed, increasing the chances of survival following an MI.
Although the coronary arteries only receive around 4 per cent of the total blood flow, the continually active myocardium is responsible for approximately 11 per cent of the body’s total oxygen consumption. This heavy demand for oxygen renders the myocardium susceptible to many factors which can compromise blood flow, particularly narrowing of the coronary vessels due to atherosclerotic occlusion.
Figure 3.9 The coronary arteries
Coronary artery disease (CAD)
Coronary artery disease (CAD) is the leading cause of heart disease in the UK and worldwide (Bailey and Hall, 2006). The most common form of CAD is caused by atherosclerotic occlusion which is characterised by a slow build-up of fatty plaque which progressively hardens and occludes the vessels. The process of atherosclerotic occlusion usually follows damage to the delicate endothelial layer that is in contact with the blood. Today many factors are known to cause endothelial damage and therefore to precipitate and accelerate atherosclerosis, including smoking, high blood pressure and high blood glucose, e.g. in patients with diabetes mellitus.
During this process the diameter of the coronary arteries is significantly reduced by a gradual build-up of fatty plaque. Atherosclerotic plaque is dense and has a consistency similar to candle wax which causes a hardening to the vessel wall and reduction in the flexibility of the artery. CAD by itself is the greatest single cause of death in the UK; the figures from 2012 indicate 16 per cent of male deaths and 10 per cent of female deaths were from CAD (predominantly as a result of MI) and this equates to around 74,000 deaths (British Heart Foundation, 2014). CAD is usually diagnosed using a stress ECG (S-T depression) and subsequent angiography which allows the diameter of the coronary arteries to be visualised.
CAD and angina pectoris
As coronary vessel occlusion progresses in CAD patients, less oxygenated blood is delivered to the myocardium and the cardiac muscle cells are forced into anaerobic respiration with lactic acid accumulation. This build-up of lactic acid produces a heavy sensation that is often experienced as central chest pain behind the breastbone. This painful sensation that is associated with CAD is referred to as angina pectoris and commonly spreads from the chest, down the left arm and frequently up the left side of the neck into the left side of the jaw.
Angina can be subdivided into stable angina, where the pain is brought on following physical exertion such as walking up a hill, and unstable angina, where the pain is often unpredictable, frequently occurring without physical exertion at apparently random times during the day and night. Unstable angina is a serious clinical finding since it is often seen in patients prior to suffering an MI.
CAD and myocardial infarction (MI)
A major danger with progressive CAD is that narrowed coronary arteries can easily become completely blocked by a thrombus (clot) or a dislodged piece of fatty plaque. Frequently an area of plaque will rupture, activating the clotting cascade, leading to rapid thrombosis and total vessel occlusion that is indicative of an MI (heart attack).
During infarction the cardiac muscle cells of the myocardium are deprived of oxygen and begin to die. Most MIs result in a characteristic, concentric pattern of tissue damage made up of the area of necrosis (dead tissue), the area of injury (living but damaged tissue) and the ischaemic zone (healthy living tissue but with reduced oxygen supply).
All three concentric areas surrounding the occlusion will collectively reduce the heart’s ability to function as an effective pump.
Although MI can come on suddenly and without warning, often a variety of symptoms are initially present. These can include chest pain, shortness of breath (dyspnoea), increased sweating (hyperhidrosis), feeling of impending doom (severe anxiety), confusion or lethargy (NHS, 2018); you may remember all of these were present in George’s case study at the beginning of this chapter. However, not everyone will experience MI in the same way; older women often present atypically with research indicating that less than half of women over the age of 75 experienced chest pain during MI (Milner et al., 2004).
To develop your knowledge of heart disease, read through Gloria’s case study before attempting Activity 3.3.
Case study: Gloria – peripheral oedema
Gloria is a chatty 86-year-old woman living on her own in sheltered accommodation. For the last 20 years she has suffered chest pain on exertion and five years ago she suffered a major MI followed by two less serious infarctions. Gloria has had stents fitted but based on her health was judged as not fit enough for bypass surgery. During your visit Gloria has been complaining of swollen feet and ankles which, while not painful, are preventing her from wearing even her slippers.
Nurses are required to carefully assess the health status of their patients and draw accurate conclusions based on medical history and current observation.
Activity 3.3 Critical thinking
Based solely on the information that has been provided in the case study, what conclusions can you draw about Gloria’s clinical history and the possible cause of her ankle and foot swelling?
We have now examined the structure and function of the heart and blood vessels which work together to enable adequate circulation for healthy tissue perfusion. To ensure that blood is delivered to all regions of the body, an adequate blood pressure must be maintained and regulated.
Blood pressure
Nurses routinely measure blood pressure (BP) using a device termed a sphygmomanometer (sphyg). Because of the past history of using mercury column sphygs (rarely used today because of the toxicity of mercury), BP readings recorded using digital, mercury-free devices are still expressed in mmHg.
A typical reading
