Heart disease (8) Arrhythmias: Part 2
The first part of this article (PJ, 20 September, pp368–70) outlined the mechanisms controlling normal heart rate and rhythm, and the management of bradycardias and some atrial tachycardias. This second part focuses on the management of atrial fibrillation and ventricular tachycardia.
Atrial fibrillation (AF) is the most commonly occurring supraventricular tachycardia — present in one in 20 people over the age of 65 years in the United Kingdom. The condition is not acutely life threatening, but neither should it be considered benign — AF is a major cause of morbidity and almost doubles mortality. The main danger is a five-fold increase in stroke and many studies have commented that better treatment of AF could substantially reduce the burden of illness in society, particularly through stroke prevention.
The incidence of AF increases with age and it is commonly caused by hypertension, ischaemic heart disease or structural heart diseases (eg, cardiomyopathy and constrictive pericarditis). Non-cardiac risk factors include diabetes, thyrotoxicosis, high alcohol intake and chronic obstructive airways disease. Despite AF being responsible for most arrhythmia-related hospital admissions, only about one-third of cases ever present to hospital, suggesting that many cases can be successfully managed in primary care.
AF is characterised by an irregular, rapid atrial rate (usually between 300 and 600bpm), which occurs secondary to chaotic conduction of electrical impulses within the atria. Unco-ordinated, small, multiple re-entry circuits (localised circling of electrical impulses) lead to asynchronous electrical activity, loss of atrial systolic function and an irregular ventricular response. The ventricular rate in AF is limited by the atrioventricular (AV) node’s inability to conduct these disorganised atrial impulses and does not usually exceed 180bpm.
Diagnosis of AF should be made using an electrocardiogram (ECG), which shows an absence of consistent P waves (indicating the lack of organised atrial activity) before each QRS complex. P waves are replaced by “f” or “fibrillation” waves; rapid oscillations varying in size, shape and timing. The ECG will also demonstrate the irregular ventricular rate (see Figure 1).
AF is generally described as either acute (present for less than 48 hours) or chronic (persisting for more than 48 hours). Chronic AF can be further classified as paroxysmal, persistent or permanent (see Panel 1, p 548).
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Citation: The Pharmaceutical Journal URI: 10988996
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