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may develop into more serious arrhythmias such as ventricular tachycardia.

      Atrial fibrillation (AF)

      This common arrhythmia is characterised by the rapid and uncoordinated contraction of the atria (fibrillation) which can reduce ventricular filling. Since the atria are only responsible for the last 33 per cent of ventricular filling, symptoms of AF such as weakness, dizziness or breathlessness may only be experienced during exercise or periods of excitement when cardiac output increases. Some individuals may never experience symptoms even with long-standing AF and are only diagnosed following a routine check-up. During periods of sustained AF the uncoordinated irregular contractions cause turbulent blood flow, allowing blood to collect in the atrial recesses, particularly in the left atrial appendage. This static blood can remain for long periods and begin to coagulate, resulting in a progressively enlarging clot (thrombus).

      At any time, these thrombi can embolise and travel up into the cerebral circulation, resulting in stroke. If only small clots are dislodged then transient ischaemic attacks (TIAs) may occur, but if clots forming in the left atrial appendage are large and embolise, major cerebral vessels may be occluded, leading to severe CVAs that may be fatal. It has been estimated that the risk of thromboembolic stroke increases around fivefold in patients with persistent AF (Wolf et al., 1991), and so to minimise risk these patients are usually placed on long-term anticoagulation therapies such as warfarin or apixaban.

      AF is commonly seen in patients with coronary artery disease or in those that have previously suffered MI; however, age is recognised as the major risk factor for developing AF (Steenman and Lande, 2017). AF is readily diagnosed by reference to a patient’s ECG where the presence of multiple P waves and an irregular heart rate are commonly observed. Since AF is so frequently encountered by nurses, to further your understanding of this important arrhythmia read through Gerald’s case study before attempting Activity 3.2.

      Case study: Gerald – atrial fibrillation

      Gerald is a 62-year-old man who recently visited his GP complaining of feeling constantly tired and washed out and experiencing breathlessness when climbing his stairs and doing his gardening. His GP noted that his pulse rate was high at 107 bpm and was also very irregular, and he was referred to a local cardiac clinic where he was diagnosed with persistent atrial fibrillation. Following unsuccessful cardioversion (where a controlled electrical shock is given to restore sinus rhythm), Gerald was prescribed apixaban and a beta blocker (sotalol) to manage his condition. Gerald has been taking his medication sporadically. Two days ago Gerald was admitted to hospital after suffering a minor stroke and on questioning it was discovered that he had stopped taking his apixaban, which almost certainly increased the coagulability of his blood, leading to his stroke.

      From the case study above it is apparent that Gerald is still unclear about the risks associated with his condition. A key role of nurses is to help educate patients and explain the purpose of their medications. Activity 3.2 highlights this role.

      Activity 3.2 Communication

      Describe how you would explain the nature of his condition to Gerald and highlight why it is important that he should take all of his prescribed medications.

      This activity highlights the importance of communication between nurse and patient in encouraging compliance with treatment regimes. While AF is a common chronic but manageable arrhythmia, other rhythm disturbances are emergencies requiring immediate medical intervention.

      Ventricular fibrillation (VF)

      Ventricular fibrillation is a serious life-threatening arrhythmia that commonly occurs following major MIs, chronic heart disease and occasionally following an electrical shock. During VF the ventricles are not contracting in an organised manner and the heart can no longer function as an effective pump. Unless the heart can be restored to its original sinus rhythm via the use of a defibrillator, the patient will die. VF is usually very clear on an ECG since no QRS complexes or sinus rhythm are visible.

      In the first part of this chapter we examined how the heart functions as an efficient pump to ensure continuous circulation of blood. We now need to explore in greater detail the role played by blood vessels in distributing blood and maintaining blood pressure.

      Blood vessels: the vasculature

      Amazingly, the human body has between 60,000 and 100,000 miles of blood vessels which function as conduits through which our 5 litres of blood is continuously circulated. There are three major types of blood vessel: arteries, veins and capillaries.

      Arteries and veins are the largest blood vessels and both consist of three distinct layers (tunics) of tissue, outlined in Figure 3.7.

       The tunica externa: This is the protective outer layer of the vessel composed predominantly of collagen-rich connective tissue. It is usually continuous with the surrounding tissues, serving to anchor the blood vessel in position within the body and prevent vessel movement following ejection of blood from the heart or during the physical movement of the body.

       The tunica media: Composed of involuntary smooth muscle, this middle layer can contract (vasoconstriction) or dilate (vasodilation) to change the diameter of the blood vessel and alter the rate of blood flow. The tunica media is much thicker in arteries than in veins since arteries are usually carrying blood under high pressure and their walls require extra reinforcement. The smooth muscle layers are innervated by sympathetic nerve fibres which are under the influence of the vasomotor centre within the medulla oblongata of the brain. This is the region of the brain that regulates vascular tone and therefore blood pressure by controlling the processes of vasoconstriction and vasodilation.

       The tunica intima: This is the thinnest and innermost layer of the blood vessel. It is composed of a single layer of incredibly smooth squamous epithelial cells (the endothelium) and is separated from the smooth muscle cells of the tunica media by a thin layer of collagen-rich tissue termed the lamina. In arteries the smooth, silky nature of this innermost layer affords minimal resistance, ensuring that blood flows rapidly in concentric layers (laminar blood flow).

      Figure 3.7 The internal structure of an artery and vein

      Arteries

      Arteries are muscular, pulsatile, elastic blood vessels that circulate blood under high pressure with most carrying oxygenated blood away from the heart. The aorta is the major systemic artery and has a greater stretch than other arteries because its walls have a higher elastin content. It carries blood directly away from the left ventricle of the heart into the systemic circuit. On exiting the left ventricle, the aorta curves over the superior portion of the heart (aortic arch), delivering blood into its descending portion which branches and supplies blood to the major abdominal and pelvic organs. The major arteries of the body are typically named according to the organ or region that they supply, e.g. the hepatic artery supplies blood to the liver, the splenic artery to the spleen and the renal arteries to the kidneys. The large arteries continually subdivide into smaller and smaller vessels before eventually terminating in arterioles which are the smallest arteries of the body.

      Capillaries

      Arterioles supply high-pressure blood directly into complex vascular structures termed capillary beds (Figure 3.8). These function as distribution vessels ensuring that all cells within a tissue or organ are adequately perfused with oxygenated blood. It is useful to visualise capillaries as completing the circuit of blood flow by forming bridges between the arteries and veins of the body. Pre-capillary sphincters are tiny rings of smooth muscle which act as valves to regulate the flow of blood into each capillary bed; these are under the control of the autonomic nervous system and a variety of locally acting chemical signals and hormones.

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