Supraventricular tachycardia is a term that doctors use to describe fast beating of the heart from an area at the top of the heart - that is any area anatomically above the ventricles. Whilst technically atrial fibrillation is a supraventricular tachycardia, it is usually considered separately both because it has different mechanisms of occurring and because the treatment and possible complications are also different.
The usual character of a supraventricular tachycardia is a fast regular beating of the heart most often in the range of 150 beats per minute to 250 beats per minute and when seen on the ECG these beats look identical to the normal beats albeit occurring at a much faster rate.
Some patients will not be aware of their heart rhythm disturbance but most will have symptoms and the commonest symptom is the sensation of the fast pounding of their heart. Others may feel sweaty or clammy, dizzy or faint or have an uncomfortable fluttery feeling in the throat. Characteristically, the rhythm disturbance comes on spontaneously and it may last for seconds or even hours before terminating spontaneously. Most patients cannot identify any obvious precipitating stimuli that cause their palpitations to occur, although in some they may recognise that excitement or emotion, physical exercise, alcohol or caffeine appear to cause the attacks.
A few patients may feel soon after the onset of the attack that they have a full bladder and want to pass water and this may be a recurrent symptom whilst the attack is occurring. This is because the muscle wall of the heart contains chemicals called natriuretic peptides which can be released into the blood stream with the excessive activity of the heart muscle and stimulate the kidneys to produce more urine.
Many people who suffer with supraventricular tachycardias (SVTs) find that the symptoms are short lived and only occur infrequently and are happy to sit out the attacks without any intervention or taking any long term treatment. Others, however, find the attacks prolonged and uncomfortable or disabling and need interventions to abort the attacks when they occur. Simple manoeuvres that the patient can try themselves are the Valsalva manoeuvre (see below), pressing on the neck over the big arteries that run up into the head (carotid arteries), splashing the face with cold water or sucking ice cubes or gently pressing on the eyeballs (with the eyelids closed!). If none of these manoeuvres work and the attack persists then it usually worth attending your local Accident and Emergency Department or Cardiology Department where the heart rhythm disturbance can be confirmed by ECG and a drug injected into a vein in the arm to stop the attack (the drug usually used is called Adenosine and has been introduced in the last few years and is usually remarkably effective in stopping the attacks). Very occasionally it may be necessary to give somebody a short acting general anaesthetic and apply an electric shock across the front of the chest (DC cardioversion) to restore a normal heart rhythm but this is really very unusual with a supraventricular tachycardia.
If a person is prone to recurrent attacks then taking medications to try to prevent attacks occurring in the first place may be necessary and probably the most effective medications in preventing attacks are Beta-blockers. In patients who cannot tolerate Beta-blockers because of contraindications or side effects such as asthma, then Verapamil can be a useful alternative. Other drugs that might be used are Disopyramide, Propafenone and Quinidine.
Very occasionally in patients who have severe, prolonged and recurrent attacks which do not respond adequately to treatment further specialised investigations called electrophysiological studies (EPS) are required to try and identify the tissue in the heart through which the electricity is travelling such that this can be burnt out using heat or electricity so that the rhythm disturbance will not recur. This is particularly likely to be the case where somebody has been born with extra conducting tissue in the area around or within the AV node which provides a shortcut around the AV node which in certain circumstances can allow the electricity to split up into two wave fronts, one going forward around the node and down into the ventricle and the other looping back on itself up into the AV node which can then set up a circuit rhythm travelling quickly around within the node both starting and perpetuating the fast rhythm disturbance. Patients with such an anatomical problem can sometime be identified by their resting ECG (although the changes on the ECG may be intermittent and therefore not always seen) and the abnormality is named after the doctors that first described it: one such abnormality being the Wolff-Parkinson-White Syndrome and another being the Lown-Ganong-Levine Syndrome.
In certain patients the Valsalva manoeuvre can be extremely effective in aborting supraventricular tachycardias.
It is a mechanism of stimulating the vagus nerve - a nerve that is responsible for slowing the heart by releasing a chemical called acetylcholine which influences the rate at which the heart pacemaker discharges and also the speed with which electricity can be conducted through the AV node. To perform the Valsalva manoeuvre you should close off your throat and then build up the pressure in your chest trying your hardest to push air out through your closed throat and try and maintain that pressure in the chest for 15 seconds or more. In some people the effect is enhanced while squatting whilst performing the manoeuvre.
As with all heart rhythm disturbances the effective diagnosis of the condition is achieved by getting a recording of the heart tracing during an attack and the various monitors that might be used can be found by following the link to tests and investigations.
Here is an ECG showing an SVT at a rate of 200 beats per minute. You can see that the beats are narrow and are regularly spaced.
Below is a diagram of the heart with the various structures labelled.
The second diagram shows an animation of the electrical activity in the heart during an SVT. It demonstrates three normal (sinus) beats followed by a burst of ten beats of SVT. It can be seen that during the SVT the electrical activity shows a wavefront that doubles back on itself stimulating the AV node before the next sinus beat can occur setting up a rapid 'circuit' rhythm around and through the node causing the heart to beat faster.
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In the absence of any abnormal physical finding when examined by an experienced doctor and in the presence of a normal resting ECG, it is very unlikely that there is any other underlying cause for the SVT, but in certain circumstances your doctor might advise that you have an exercise test or echocardiogram to exclude other possible causes such as coronary disease, cardiomyopathies or valvular heart disease.
Unlike atrial fibrillation supraventricular tachycardia does not carry with it the risk of developing stroke and therefore medications such as Aspirin or Warfarin are not required for those people who suffer from supraventricular tachycardia.