[Applause] [Music] hi this is tom from zero2finals.com in this video i'm going to be going through supraventricular tachycardia and you can find written notes on this topic at serialdefinals.com learn or in the cardiology section of the zero to finals medicine book i want to start by saying this video is designed to help your understanding of svt in preparation for exams and not to guide your clinical practice always check the national and local guidelines and consult experienced seniors when you're treating patients so let's jump straight in supraventricular tachycardia refers to a fast heart rate which is called tachycardia that's caused by abnormal electrical signals that come from above which is what supra refers to the ventricles and this means it essentially comes from the atria let's start by talking about the pathophysiology in normal circumstances the electrical signals of the heart start in the cyanoatrial node and this is located at the junction between the superior vena cava and the right atrium the electrical signals then travel through the right and the left atrium causing an atrial contraction then it travels through the atrioventricular node and down to the ventricles where it causes a ventricular contraction normally the electrical signal in the heart can only go in one direction from the atria to the ventricles normally electricity cannot pass from the ventricles back into the atria in most cases of superventricular tachycardia it's caused by the electrical signal re-entering the atria from the ventricles once the signal is back in the atria it travels back through the av node to the ventricles again and causes another ventricular contraction this causes a self-perpetuating electrical loop without an end point and results in a fast narrow complex tachycardia paroxysmal supraventricular tachycardia or paroxysmal svt describes a situation where the svt reoccurs and remits in the same patient over time in between which there are periods of normal sinus rhythm let's talk about narrow complex tachycardia svt typically causes a narrow complex tachycardia meaning the duration of the qrs complex is less than 0.12 seconds on a normal 25 millimeter per second ecg 0.12 seconds equates to three small squares so the qrs complex in svt will fit within three small squares on an ecg svt looks like a qrs complex followed immediately by a t wave then another qrs complex and then a t wave and so on there are four main differentials of a narrow complex tachycardia and these are sinus tachycardia svt atrial fibrillation and atrial flutter there are key features that will help you differentiate between these different diagnoses you should be able to spot sinus tachycardia on an ecg as this will have the normal p wave qrs and t wave pattern sinus tachycardia is not an arrhythmia and is usually a response to an underlying cause such as sepsis or pain and the mainstay of management is to treat the underlying cause in supraventricular tachycardia the qrs complexes are regular which help you differentiate it from atrial fibrillation where the qrs complexes will be irregularly irregular in atrial flutter the atrial rate is usually around 300 beats per minute and it gives a sawtooth pattern on the ecg with a qrs complex occurring at regular intervals depending on how often there is conduction from the atria to the ventricles usually this is two atrial contractions to one ventricular contraction or two p waves to one qs complex sometimes it can be difficult to distinguish between the different causes so always seek help from an experienced person when you have any doubts svt can also cause a broad-based tachycardia if the patient also has a bundle branch block i won't go into too much detail about this but it's worth bearing in mind for now just remember that svt causes a narrow complex tachycardia so let's talk about the types of svt and there are three main types of svt depending on the source of the electrical signal atrioventricular nodal reentrant tachycardia is when the re-entry point is back through the av node so the electricity passes from the atria through the av node into the ventricles and then back through the av node into the atria again atrioventricular re-entrant tachycardia is when the re-entry point is an accessory pathway this refers to an additional electrical pathway somewhere between the atria and the ventricles that lets electricity back through this is the most common type of svt having an extra electrical pathway in the heart is called wolf parkinson white syndrome this electrical pathway might not cause any symptoms or it might cause episodes of svt the extra electrical pathway may be seen on a routine ecg as a slurred upstroke in the qrs complex and this is called a delta wave there will also be a short pr interval this change on the ecg is caused by the electricity prematurely entering the ventricles through the accessory pathway finally there's atrial tachycardia and this is where the electrical signal originates in the atria somewhere other than their sino-atrial node this is not caused by a signal re-entering from the ventricles but instead from abnormally generated electrical activity in the atria this ectopic electrical activity causes an atrial rate above 100 beats per minute let's talk about the acute management of stable patients with supraventricular tachycardia when managing svt in a stable patient we take a stepwise approach trying each step to see whether it works before moving on to the next one the patient should be on continuous ecg monitoring so that you can monitor in real time the electrical activity of the heart the first thing to try is the valsalva maneuver and this can be done by asking the patients to blow hard against resistance for example blowing into a plastic syringe the next thing to try is carotid sinus massage and this involves massaging the carotid on one side gently with two fingers often these simple measures without using any medication will be enough to convert the patient back to sinus rhythm if these measures don't work then the next step is adenosine and we're going to talk in more detail about that shortly an alternative to adenosine is varapamil which is a calcium channel blocker and this is used where adenosine is contraindicated usually these measures will be successful in rare cases where they failed the patient may need electrical cardioversion so let's talk in more detail about adenosine adenosine works by slowing cardiac conduction primarily through the atrial ventricular node it interrupts the av node or accessory pathway during svt and resets it back to sinus rhythm the half-life of adenosine is less than 10 seconds meaning it's very quickly metabolized and stops having an effect it needs to be given as a rapid bolus so that it reaches the heart quickly and with enough impact to interrupt the pathway for a short period it will often cause a brief period of asystole or bradycardia that can be scary for both the patient and the doctor however it's very quickly metabolized and their normal sinus rhythm should return there's a few key points on administering adenosine it needs to be avoided if the patient has asthma copd heart failure heart block or severe hypotension it's important to warn the patient about the scary feeling of dying or impending doom that will happen when the adenosine is injected although this is only short-lived and the patient will feel back to normal as soon as the effects wear off it needs to be given as a fast intravenous bolus into a large proximal cannula for example a gray cannula in the anti-cubital fossa and as soon as it's been injected the canyon needs to be flushed fast in order to push the medication as quickly as possible to the heart where it needs to take action the doses are initially six milligrams then 12 milligrams and then a further 12 milligrams if no improvement occurs between the doses next let's talk about management in unstable patients when we talk about unstable patients we mean patients that have been compromised by superventricular tachycardia and these are patients who've got a raised respiratory rate chest pain hypotension signs of heart failure or poor perfusion treating unstable patients with svt involves using synchronized cardioversion with a defibrillator usually done under sedation or general anaesthetic synchronized cardioversion means the defibrillator monitors the electrical signals of the heart particularly trying to identify the r waves an electric shock is synchronized with the ventricular contraction so that the shock occurs at the correct time the shock will occur at the r wave on the ecg and if successful it'll be followed by sinus rhythm the reason synchronized cardioversion is used in patients that still have a pulse is that we need to avoid shocking the patient during a t wave if you deliver a shock during a t wave it can cause ventricular fibrillation and send the patient into cardiac arrest unstable patients may also require amiodarone to help with restoring the normal electrical activity let's talk about long-term management of patients with paroxysmal svt when patients develop recurrent episodes of svt then measures can be taken to prevent these episodes from occurring and the options for this are medications such as beta blockers calcium channel blockers or amiodarone and radio frequency ablation let's talk in more detail about radio frequency ablation catheter ablation is performed in an electrophysiology laboratory often called a cath lab it involves a local or general anaesthetic inserting a catheter into the femoral vein and feeding a wire through the venous system under x-ray guidance up to the heart once the wire is in the heart it's placed against different areas to test the electrical signals in that area this way the operator can hopefully find the location of any abnormal electrical pathways the operator may try and induce the arrhythmia in order to make the abnormal pathways easier to find once the abnormal pathway is identified radio frequency ablation which is essentially heat is applied to burn the abnormal area of electrical activity this leaves scar tissue that does not conduct electrical activity and the aim is to remove the accessory pathway that's causing the arrhythmia radiofrequency ablation can be curative for certain types of arrhythmia caused by abnormal electrical pathways and these can include supraventricular tachycardias wolf parkinson white syndrome atrial flutter and atrial fibrillation thank you for watching this video if you liked the video left a comment or subscribe to the channel thank you so much it really helps zero to finals is not just a youtube channel there's also a website with detailed notes illustrations and questions an instagram account where new questions are posted every day to help you test your knowledge books flash cards and much more i also have a personal channel where i share my thoughts and tips on learning medicine and you can find links to everything in the description of this video see you next time