Supraventricular Tachycardia
What is Supraventricular Tachycardia?
An SVT is an abnormally fast heart rate whereby the heart rate is in excess of 100 beats per minute. They often start abruptly and stop abruptly and occur because of abnormal electrical pathways within the heart.
What are the typical symptoms?
It is very common to experience palpitations (an abnormal awareness of heart rate). If the heart rate is extremely fast patients can experience chest pain, dizziness, breathlessness and can feel light headed.
What are the causes of an SVT?
SVT is generally the result of an abnormal heart electrical activity. A common form of SVT is called AVNRT with other common forms being associated with conditions such as Wolff-Parkinson-White syndrome (WPW syndrome). Having an SVT does not necessarily mean you have an abnormal heart and often the causes are simply “an electrical glitch” that is easy to treat with either medical treatment or catheter ablation. SVTs can occur at any age and patients can present with them for the very first time in late adult life. They are generally triggered by ectopic or extra heart beats which are often the catalyst that set off the fast sustained SVT. SVTs can last for minutes, hours or even days.
What are the types of SVT?
SVT is generally the result of some abnormal heart electrical activity. A common form of SVT is called AVNRT with other common forms being associated with conditions such as Wolff-Parkinson-White syndrome (WPW syndrome). Having an SVT does not necessarily mean you have an abnormal heart structure and often the causes are simply “an electrical glitch” that is easy to treat with either medical treatment or catheter ablation. SVTs can occur at any age and patients can present with them for the very first time in late adult life. They are generally triggered by ectopic or extra heart beats which are often the catalyst that set off the fast sustained SVT. SVTs can last for minutes, hours or even days.
Most episodes of SVT are self-limiting and short lived and don’t necessarily require treatment. If however symptoms become very frequent or are sustained treatment can become necessary. Patients can terminate SVT themselves by using manoeuvres such as Valsalva manoeuvre (a type of straining) which can slow down the electrical impulses that travel through the central electrical junction box (the AV node) and make the SVT stop. The Valsalva type manoeuvre usually involves pinching your nose, closing your mouth and trying to strain as though you were on the toilet. If this doesn’t get rid of the SVT then splashing your face with ice cold water or even swallowing crushed ice in a drink quickly can again terminate an SVT. If these measures are ineffective and you feel unwell you should attend your local A&E. When you are in A&E drugs such as adenosine or beta-blockers can be used to terminate the SVT. Unfortunately this doesn’t cure the SVT and if you have had several episodes before it is likely to reoccur. This is when it’s important to see an electrophysiologist who can perform curative ablation of SVT.
Patients will usually present with palpitations. It is vitally important that we capture the typical symptoms on paper ideally in the form of an ECG. That means if you are having typical symptoms it’s important that we get a record of what your heart rate and rhythm are doing at the time of them. By looking at this ECG or rhythm strip an electrophysiologist can make a firm diagnosis and advise on treatment. Sometimes patients can purchase their own heart monitor which can adapt to their smartphone, such as a ‘Kardia’ device. This allows them to capture a single lead ECG strip of what their heart rhythm is doing when they have an attack of their typical symptomatic SVT.
The treatment depends on the severity and frequency of the symptoms and also the type of SVT involved. If SVTs do not cause too much problem then simple Valsalva/vagalmanoeuvres that patients can perform themselves maybe enough to keep symptoms under control.
If symptoms do start to become a problem then treatment options can extend to drug therapy or an EP study and ablation. Catheter ablation for SVT is one of the most straight forward procedures anelectrophysiologist performs. This involves freezing the groin at the top of the right leg (see picture) with local anaesthetic and then introducing 3 or 4 fine catheters into the heart under X-ray control.
The electrophysiologist will then try and trigger the SVT whilst the recording electrodes are inside the heart. The patient does not feel the electrodes when they are in the heart. When the electrophysiologist is able to trigger the SVT they are then able to make an interpretation of the electric signals coming from the heart and determine what and where the problem is arising from. That will then allow them to treat the SVT. The most common forms of SVT can be ablated easily. They would generally carry a 90-95% chance of cure with one procedure.
These are generally safe procedures to perform and typically take between 60 and 120 minutes. They are usually done whilst the patient is sedated rather than fully asleep. The main risks for the procedure is that the patient’s natural pacemaker cells can become damaged and lead to a condition called “heart block”.
If this happens (typically 1/100-1/150 cases) a pacemaker may be required. Patients are usually treated on a day case basis and are in and out of hospital on the same day although occasionally an overnight stay maybe required. The advantages of this type of treatment are that it is usually curative and patients will no longer need to take medication long term.
After the procedure a patient is not allowed to drive for 48 hours.
Typically in the follow up period a heart recording (ambulatory heart monitor) will be performed as an out-patient and then a review consultation, in conjunction with an ECG will be performed.
Other options to treat SVT include tablets such as beta-blockers and calcium blockers (verapamil and diltiazem) but these do not cure the SVT and may only control it-furthermore the tablets to be taken long term to manage it.
Fine electrode Catheters are placed under local anaesthetic and sedation from the top of the right leg into the heart.