in conditions such as heart failure, cardiomyopathy or long-standing hypertension.
Cardiac arrhythmias
The term cardiac arrhythmia is used to describe any changes to the transmission of action potentials through the cardiac conductive system that leads to an abnormal heart rhythm or heart rate. Many arrhythmias such as simple ectopic beats are benign with no major physiological effects, while others may result in a heart that pumps blood less effectively, leading to a reduction in cardiac output. In the most severe arrhythmias cardiac output may cease completely, leading to sudden cardiac death.
Changes to the cardiac conductive system
By the age of 50 around 50–75 per cent of the pacemaker cells of the heart’s natural pacemaker SAN have been lost, while the cardiac muscle fibres of the atrioventricular bundle (bundle of His) undergo varying degrees of fibrosis. These changes may reduce the efficiency of cardiac conduction and contribute to the increased risk of ectopic beats (palpitations) seen in older people.
Ectopic beats
Two major types are recognised and are classified according to which chambers are affected. Premature atrial contractions (PACs) occur when there is an early contraction of the atria and can usually be recognised on an ECG as an extra P wave. PACs are minor events and often not even perceived by the patient. Premature ventricular contractions (PVCs) occur as a result of early contraction of the ventricles; these are usually more noticeable to the patient. Often the patient will complain that it feels as if their heart has paused (or lurched) in their chest followed by a more powerful subsequent recovery beat.
Frequently PVCs may be experienced in clusters or in predictable patterns before disappearing and returning hours, days or even months or years later. Since PVCs occur as a result of abnormal conduction in the ventricles, they are more easily recognisable as irregular spikes on an ECG that interrupt the normal sinus rhythm. Most PVCs, while quite scary for the patient, are benign and often related to stress, dehydration or use of stimulants such as caffeine or nicotine. They are also very common in women going through the menopause. When PVCs occur sequentially one after the other, they 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
