Cardiac arrhythmias

Aetiology and epidemiology
Cardiac arrhythmias are a disturbance of cardiac electrical impulses from normal sinus rhythm, and present as palpitations or with the symptoms of reduced cardiac output, such as chest pain, dyspnoea, light-headedness, dizziness or blackouts with a rapid recovery.

Palpitations often follow increased cardiac output due to exercise, emotion or stress, and are common particularly in the elderly.

The normal heart rate in adults is 60–100bpm. The term tachyarrythmia is used to describe three consecutive complexes occurring at more than 100bpm, while rhythms producing cardiac slowing are bradyarrhythmias.

AF is a tachyarrhythmia with uncoordinated atrial activation, and is diagnosed by fibrillating low-voltage atrial activity at more than 300bpm and an irregular ventricular response. AF affects 1 per cent of the population, and the prevalence increases with age.

Atrial mechanical function deteriorates and with it ventricular filling. When it is associated with a rapid heart rate the result is cardiac failure. The atrial dilation and loss of function may be associated with the development of thrombus and the risk of stroke. AF may be intermittent or permanent.

National service framework
The NSF for CHD recommends expert assessment of patients in whom an arrhythmia is suspected, and development of care pathways and arrhythmia specialist services.

The NSF includes guidance on who should be referred urgently, targeting those with syncope, complete heart block and ventricular tachycardia (VT).

Delivery of appropriate care with implantable defibrillators, pacemakers and catheter ablation may either lead to a cure, or even improve long-term survival. 

Diagnosis
Patients are usually asymptomatic at the consultation and the doctor has to rely on the history in making the diagnosis. Taking an accurate history is very important, and the history from an observer may be very helpful if the patient has collapsed.

Several questions can help with diagnosis. What is the character of the palpitations? It may be helpful to ask the patient to tap out the rhythm of the palpitations.

The frequency will determine the method of investigating the symptom, as a 24-hour tape will only be of value if symptoms occur almost daily.

Establish the pattern of onset. An abrupt onset suggests a cardiac arrhythmia. Find out if there were there any trigger factors. Palpitations during exercise suggest adrenergic involvement or a response to beta-blocker.

Abrupt termination of symptoms suggests an arrhythmia; a gradual termination does not rule one out.

Syncope has prognostic value because it may be associated with fast supraventricular tachycardia (SVT) or VT.

It is useful to know what drugs the patient is taking, for example, asthma medications or vasodilators such as nifedipine. Nicotine, alcohol or drugs could be triggering attacks.

Could other conditions exacerbate the problem? Coronary artery disease, thyrotoxicosis, mitral valve prolapse; pregnancy and gastro-oesophageal reflux might be associated with palpitations. AF is often detected during the investigation of cardiac failure symptoms.

Electrocardiogram
An accurate diagnosis requires a 12-lead ECG to record the abnormal rhythm. Even in the absence of an episode it may indicate the aetiology of the arrhythmia.

Look for evidence of atrial depolarisation, such as P waves or flutter waves.

It is important to observe the rate of the atrial and ventricular depolarisation. Look at the relationship between the atrial activity and ventricular depolarisation.

A short PR interval measured from the beginning of the P wave to the start of the QRS complex could indicate Wolff-Parkinson-White or Lown-Ganong-Levine syndromes.

Are the ventricular complexes of normal width? Are the impulses conducted through the normal cardiac pathways, such as SVT, or a broad complex rhythm such as SVT with aberrant conduction or VT?

Is the cardiac axis normal? If the ventricular complexes in leads aVL and aVF are positive, then this

is correct. It is important to check for these points alongside the computer-generated report, because software that is usually very accurate may be less helpful when assessing complex arrhythmias. 

Management
NICE guidance on the management of AF sets out pathways for management and makes recommendations on both treatment and stroke risk reduction.

Rhythm control
NICE recommends rhythm control with either electrical or pharmacological cardioversion for patients with persistent AF who are symptomatic, younger, presenting for the first time, suffering from congestive heart failure or are experiencing AF secondary to a treatment.

Rate control
Rate control should be used first-line in patients with persistent AF who are over 65, have coronary artery disease or contraindications to antiarrhythmic drugs, or are unsuitable for cardioversion.

Beta-blockers or calcium-channel blockers are the recommended initial therapy for rate-control; digoxin is used first-line only in patients who are predominantly sedentary.

Stroke risk
There is also advice about stroke risk stratification for patients with persistent AF.

The absolute risk of stroke in AF ranges from <1 to 36 per cent per year in patients over 80 with additional risk factors.

In trials, warfarin has reduced stroke risk by 60 per cent and aspirin by 40 per cent, although haemorrhage is more frequent in the elderly or in patients with an INR of 3.0.

Patients are at high risk if they have had a previous thromboembolic event, are 75 or over with hypertension, diabetes or vascular disease, or have valvular heart disease or heart failure. This group should be treated with warfarin.

Patients under 65 with no underlying cardiac or cardiovascular disease are at low risk and should be prescribed aspirin 75–300mg daily.

Patients between 65 and 75 are at intermediate risk if they have not had a thromboembolic event or have a structural or functional disorder of the heart. They can be offered either warfarin or aspirin. Each must be assessed individually.

Risk changes as patients become older or have cardiovascular events.

Referral
Referral to a specialist should be considered in younger patients, patients with lone AF, or ECG evidence of an underlying electrophysiological disorder such as Wolff- Parkinson-White syndrome, in patients in whom AF may be associated with life-threatening arrhythmias, syncope with AF, or where pharmacological therapy has failed.

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