SUPRAVENTRICULAR TACHYCARDIA (SVT)
The supraventricular tachycardia is a type of arrhythmia characterized by rapid, sustained palpitations that start and stop abruptly.
The heart is made of 4 cardiac cavities called chambers.
The superior part is composed of the left and right atriums (LA-RA) while the left and right ventricles (LV-RV) form the inferior part of the heart.
This organ is the motor of life and these 4 cavities act as reservoirs for the blood. When the heart contracts, it pumps and propels the blood all over the organism.
To properly function, this pump needs an electric thrust in order to determine the number of beats per minute.
The cardiac electrical system
The heart’s electrical system produces this thrust and its different components are responsible for effectively synchronizing its contraction, that is, from the bottom towards the top.
Like the electrical system of a house
The heart has an electrical network like that of a house. It is built this way:
The electricity enters through the second story where the electric generator is found;
Afterwards, the electricity travels to the first story through one single path; this is where we find the control box;
From this box, the electricity is sent to the rooms at the bottom through specialized, high conduction wires.
Let’s see it again from the heart’s standpoint
The conductor of this electric system is situated at the top of the heart, near the right atrium.
It is an island of cells called sinoatrial node which is, in fact, the natural pacemaker of the heart. It initiates all the heart beats and determines their frequency.
This cardiac frequency or cardiac rhythm is known as the sinus rhythm because of its origin, the “sinoatrial” node.
An organised electrical transmission
The electricity generated by this node is transmitted to the atriums et ventricles by the only possible path, that is, the electrical conductor, or the atrioventricular node. This customs officer controls the speed of the electric transmission.
The electricity then makes it to the ventricles via a rapid conduction network, the Purkinje bundle.
Normal cardiac frequency
It is said that the normal heart rate is between 60 and 100 beats per minute.
It varies during the day
It is normal that the heart rate varies throughout the day.
The heart beats slower when we are at rest or because of certain medication and accelerates during physical activity or stress, for example.
The supraventricular tachycardia
A supraventricular tachycardia (SVT) is any given cardiac arrhythmia that gives a heartrate above 100 beats per minute that does not originate from the conductor of the orchestra, the sinoatrial node.
It originates from above the ventricles
It comes from the area above the ventricles, hence its name; supraventricular.
At high speed!
The usual heartrate of this type of arrhythmia is between 140 and 220 beats per minute.
A short circuit in the electric network
In some sort, it is a short circuit in the electric network with the consequence that the heart beats rapidly even if the person is at rest, without any exterior stimulation.
This anomaly is not hereditary. It has nothing to do with the presence or not of blocked heart arteries.
Who is concerned?
The SVT’s may be present in children as much as in adults of all ages, even those who have a good health.
What are the symptoms?
An SVT usually manifests itself suddenly with palpitations and end as rapidly as they began with the return of a normal heartbeat.
It can give the impression of practicing an intense sport with the feeling that the heart wants to come out of the body, even at rest.
A classic combination
A way to see the beginning and the ending of the palpitations is to think of turning on and turning off a light. The heart suddenly goes from, for example, an 80 to a 180 heartbeats per minute. Then, it abruptly returns to 80 beats per minute. This type of description quickly orients the health professional to an SVT diagnostic.
This description of the rapid start and end of a palpitation episode quickly orient the health professional towards an SVT diagnostic.
Of varied lengths
An SVT can last a few minutes.
Or, inversely, it can last a few hours or even many hours, where a visit to the emergency at the hospital is necessary in order to be given an intravenous medication to put an end to the crisis.
Other possible sicknesses
Certain people will not perceive the palpitations as rapid heartbeats, but will suddenly feel out of breath, thoracic pains or dizziness. These symptoms are caused by the high and steady heart rate.
We don’t die from it, but it is bothersome
SVT’s are not life threatening or dangerous. Rather, they affect quality of life, as they are triggered at any moment, at any time of the day or night and without any foreseeable signs.
Very variable frequencies
The frequency of the episodes varies a great deal from one individual to another and may vary in time for each person. In fact, there can be one incident in a year or two or three incidents per week. It is not a regular frequency, unfortunately.
There can be repetitive cases of SVT’s during teenage years, followed by a pause for a few years with a return at menopause or andropause.
Why and how?
There are three main mechanisms responsible for an SVT.
A short circuit in the electric conductor called nodal entrance (50 to 70% of the cases);
An extra electrical wire in the heart since birth called the electric accessory bundle (20 to 30% of the cases);
Short circuit in the atrium call paroxysmal atrial tachycardia (PAT) (10 to 20% of the cases).
In approximately 30% of the population, the electrical conductor or the atrioventricular node (AVN) area is composed of 2 electrical entrances. There is a slow conduction lane and a fast conduction lane of the AVN; it is different from the normal situation.
As long as the electricity goes through the 2 entrances at the same time, the electrical signal makes it to the ventricles simultaneously and does not cause a short circuit, or arrhythmia.
An SVT by re-entrance through the node may be triggered by the premature production of electricity called extra-systole.
An auricular extra-systole is produced either at the atrium level (auricular extra-systole or AES) or from the ventricle (ventricular extra-systole or VES).
It is most often asymptomatic, or it is felt under different forms by the individuals. Some describe it the heart pausing or a more vigorous heartbeat.
If the extra-systole enters the conductor (AV node) evenly or synchronized in the slow and fast lanes, there will not be any short circuit.
However, if the extra-systole comes up at a precise moment where one of the two electrical entries is not ready to let the electricity through, the electricity then returns solely through one lane and comes back through the other one, inversely, causing a micro electric cycle which in turn causes a paroxysmal supraventricular tachycardia (PSVT).
Accessory bundle (hidden or Wolff Parkinson White)
An accessory bundle is an extra electrical wire present at birth that links the atrium to the ventricle. This electrical wire bypasses, in a certain way, the AV node’s control. It can be situated on either the left or right side of the heart.
In certain cases, it is without consequences and won’t cause arrhythmia. In other cases, however, the extra-systoles trigger the SVT through the accessory bundle. When triggered, the electrical activity is sent down by the electrical conductor and comes back up through the accessory bundle in the opposite direction. The electrical activity is ready to descend again to the ventricle via the electrical conductor. The electrical circuit is created.
Paroxysmal auricular tachycardia (PAT)
Paroxysmal auricular tachycardia may originate in the right or left atrium. A micro-electrical circuit forms, taking over from the natural conductor of the heart and producing electricity very quickly, provoking a SVT.
Treating an SVT is variable from one person to another.
It is directly related to the frequency of the episodes, to the duration, to the felt symptoms and to the consequences on the quality of life.
Tricks to try
At times, the SVT may be stopped when using the Valsalva manoeuvres:
These consist of contracting at the stomach level, like when having bowel evacuation problems.
Another method is to rub the neck under the jaw, where the heartbeats are felt.
Or, plunging the face in ice water also helps to stop the SVT.
These actions may influence the nervous connections of the heart and put them back on their normal rate.
A prescription “in case”
The patients may also be given a prescription for a medication to be taken only if an episode happens and doesn’t stop after the Valsalva manoeuvres. This pill taken at this moment can put a stop to the arrhythmia.
A more specific medication
When the episodes are frequent and affect the quality of life of a person, doctors may begin a medication that consists of slowing down the electric conduction at the AV node.
In other cases, a different medication acting specifically on the atrium’s electricity or on the accessory bundle may be used.
The effect of the medication greatly varies. Sometimes, even if it is very efficient, it can cause secondary effects, which force the doctor to change or cease the medication.
A definitive therapy, the ablation
Another method used is to put a definite end to the SVT. The treatment that allows the healing of an SVT is the ablation through a catheter.
Ablation through a catheter consists of burning the area where the SVT is created. This type of intervention is done in specialized centres, by doctors specifically trained in this domain.
The first step of this treatment is to have an electrophysiological study (EPS) done. It allows to study the heart’s electrical activity in order to find the mechanism of the SVT.
This exam sees catheters introduced in the veins in the body and that are then directed to different parts of the heart.
These catheters record the electrical cardiac signals. This way, the specialists may precisely determine the location of the SVT and to destroy the short circuit. This intervention is done with a catheter that burns the area with heat or coldness.
The procedure has variable durations. Usually, a maximum of 2 hours is enough for the intervention to be done.
Excellent success rate
The success rates vary according to the SVT mechanisms, but on average, they are high, attaining 95% in most cases!
The risks associated with the procedure
Like any intervention, the risks are present. Major complications related to this procedure represent ≤ 1% (necessity to install a pacemaker, heart attack, heart perforation, etc.).
Minor complications may also occur, like bleeding or a hematoma formation (cluster of blood where the catheters were installed.
It is important to remember that the treatment chosen for an SVT varies from one individual to another.
The different benefits and risks of each option are presented by the health professional.
The final decision belongs to the patients and is taken after discussion.