Supraventricular tachycardia (SVT)

Author: Dr Sean Gomes

Hello my name is Dr. Gomes. I'm a cardiologist who specializes in heart rhythm problems and I'll discuss a common condition that I see which is supraventricular tachycardia or SVT and a good place to start a discussion for this problem is a review of the heart and the electrical system. So if we start with the heart itself the heart is made up of four chambers. There are the two top chambers that you can see here which of the atria right and left and the bottom chambers which are the ventricles right and left the ventricles are the pumps that squeeze blood out to the rest of the body and the whole heart all four chambers are controlled by an electrical system so I'll show those on a diagram this is a very crude diagram of the heart's electrical system but if we look here we see that there are four chambers we divide the heart into four here and all four chambers here are controlled by an electrical system so there's the sinus node at the top of the heart which we can think of as the fuse as the spark plug like the spark plug in your car there's the AV node which we can think of as a fuse box and then there are two wires that feed the bottom of the heart usually messages will start at the top of the heart travel down through the middle and through the two wires at the bottom of the heart if we do an ECG or a cardiograph what we will see on the ECG is the top then the bottom of the heart beating see the top in the bottom of the heart and this will happen each and every heartbeat so we'll see top bottom top bottom top bottom top bottom that normal heart rhythm occurs with absolutely no symptoms in patients because the heart is doing its normal activity and we wouldn't expect people people to have any symptoms at all during normal our activity SVT is a sudden disturbance of the hearts normal rhythm and it would typically occur in patients without any structural problems with the heart often will occur in younger patients with no other medical problems however SVT can also occur in some cases as people become older.

The most common cause for SVT is a situation where a patient would be born with an extra wire close to the normal electrical system there are other forms of SVT which include an extra wire away from the electric normal electrical system and finally a much rarer cause of SVT will be in an area at the top of the heart where there will be an overactive focus which will fire off and disturb the normal heart rhythm which we've shown here this is called normal sinus rhythm. A typical way that SVT will be triggered or caused in most patients will be an ectopic beat and extra beat occurring it will travel down this extra wire. This would be the most common cause of SVT if the conditions are right that extra beat will travel back up the normal electrical system and then a short circuit will develop where the heart will race very very fast in some cases patients may have had a heart rate of over 200 beats a minute because of this short circuit occurring. Things that will stop this sort of short circuit occurring in some cases may be a deep breath or the valsalva maneuver where you try and pop your ears; for instance by bearing down. That may not be effective in some patients who may need to present to hospital and have intravenous medications which are usually effective. If patients have frequent episodes of SVT there is a role for medications which can help to reduce the frequency attack of attacks if medications are not effective or are causing side effects then there is a role for procedure to stop SVT. We'll discuss that now. The procedure is an electrophysiology study or EPS and ablation.

Ablation is the part of the procedure where we treat the SVT so if we go back to the model of the heart during an EPS or electrophysiology study we introduce wires in through the vein at the top of the leg we take them up to the heart we measure the different parts of the electrical system with the wires so we measure the spark plug area we put another wire in to measure the fuse box area we measure we put a wire in to look at the two wires in the bottom of the heart and we would usually put a fourth wire in which allows us to look at the whole of the heart to both top and bottom chambers. Once those wires are in place we actually try and trigger or cause the SVT we want the heart to race and for the short circuit if that's what's causing the problem to present a set itself. Once that happens we can use the wires and special testing to confirm the cause of the SVT we'll be able to find in most cases whether it's this problem with an extra wire close to the electrical system, this problem with the wire away from the electrical system or an overactive area at the top of the heart. This problem is called AVNRT the most common form of SVT. This is called AVRT and this is called atrial tachycardia. The names are unimportant for the patient because the symptoms will be the same but for a procedure less like me it is important because the next step if we confirm the cause we have an option to take a different wire which we can heat the tip of to this area and we can cauterize this extra connection away if we find this problem. If we find this problem an extra wire over here we can also cauterize this or if we find this we can cauterize this overactive area away.

This procedure this cauterizing which is called ablation. This is the most effective treatment for SVT. For the most common form of SVT if the extra wire is here this would be associated with a 95 percent chance of success or curing the problem. For this problem around 90 percent and for the least common form we see this in less than 10 percent of cases this would still be 85 percent successful of curing the problem without a need for ongoing medication. As you can imagine with this procedure where we put wires in through veins and take them into the heart that risks can occur and we'll discuss those risks now. The most common risks involve bleeding infection blood clots and damage the surrounding blood vessels or nerves at the top of the leg here where we put the wires in.

Supraventricular tachycardia (SVT)

We can really cause damage to the heart causing bleeding around the heart. There is the chance of a heart attack or stroke. The most serious risk in a patient particularly younger patient with no other medical problems is damaging a normal electrical system which we see here which in most cases would lie close to this extra wire that we are treating.

If we damage this area we may need to fit a permanent pacemaker Thankfully that's a very rare complication of the procedure and we'd usually quote a risk of needing a pacemaker for ablation of SVT in the order of 1 in 500. A usual quoted risk for most patients if we add up all of the risks including very rare risks we would quote a usual overall complication rate with this procedure of between 1 and 2 percent. Most of those risks would relate to problems in and around the groin. Then we have the more serious risks like bleeding around the heart a stroke a heart attack or needing a pacemaker or less than 1%.

Ablation is not a definite treatment needed for all patients with this problem with SVT it would be a procedure that would be in most cases used for patients who have ongoing attacks despite medication or side effects to medications however it is the most effective treatment with rare but important risks with that we've discussed. The procedure itself would usually take between 2 and 3 hours it may be performed with sedation where your patient is given medication to help them relaxed or in some cases with a general anaesthetic. It would involve an overnight stay and we expect most patients to go home the following day with no problems. It is important to be careful with heavy lifting for 2 weeks after the procedure but after that period most patients would be back to the normal activities. I'm happy to discuss this procedure again in detail should you wish in a formal consultation.

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Supraventricular tachycardia (SVT)

Hello my name is Dr. Gomes. I'm a cardiologist who specializes in heart rhythm problems and I'll discuss a common condition that I see which is supraventricular tachycardia…

By: Dr Sean Gomes