How do arrhythmias affect people?
Arrhythmias can have a number of physiological effects which may lead to a range of symptoms.
In particular, there is a loss of the normal co-ordinated depolarisation and contraction of the atria and the ventricles, which occurs with sinus rhythm and which we have explored in previous steps. For example, in the case of atrial fibrillation, the chaotic electrical activity within the atria causes uncoordinated and ineffective contraction of the atria and therefore reduced filling of the ventricles. This is referred to as loss of the ‘atria kick’.
Diagram depicting Atrial fibrillation
© St George’s, University of London
The impaired ventricular filling reduces the amount of blood which can be ejected from the heart during each ventricular contraction (stroke volume).
Cardiac output and blood pressure may also therefore be reduced due to the following relationships:
Stroke volume ↓ x heart rate = cardiac output ↓
Cardiac output ↓ x peripheral vascular resistance = blood pressure
In addition, stroke volume may also be negatively affected by the abnormal changes in heart rate which commonly occur with arrhythmias. Atrial fibrillation, for example, is associated with tachycardia (a fast heart rate) and you might think, looking at the equations above, that this would improve cardiac output and blood pressure. The problem is that the ventricles fill when the heart is at rest, and at very fast rates the time available between beats for this filling to take place is reduced. At the other end of the spectrum, some arrhythmias are associated with bradycardia (a slow heart rate) which means there are less ventricular contractions per minute, leading to a direct reduction in output:
Stroke volume x heart rate↓ = cardiac output
Tachyarrhythmias also require the heart muscle to work harder to maintain the increased heart rate. This increased workload requires more oxygen and if this demand cannot be met by the supply of blood, the person may experience chest pain.
These negative effects on cardiac output, blood pressure and oxygen supply to the heart can lead to a range of symptoms which vary in their severity, depending on the type of arrhythmia, the underlying health of the person affected and how long they have had the arrhythmia. Possible signs and symptoms include:
- Reduced tolerance to exercise
- Shortness of breath
- Chest pain
- Loss of consciousness
- Cardiac arrest
© Kingston University and St George’s, University of London