wolf Parkinson White pattern or wpw is a type of heart arhythmia caused by an accessory pathway or an extra electrical conduction pathway connecting the Atria and ventricles or the upper chambers and the lower chambers of the heart normally an electrical signal starts at the Sino atrial or SA node in the right atrium it then propagates out through both Atria including Bachman's bundle in the left atrium and contr racts both Atria it's then delayed just a little bit as it goes through the atrio ventricular or AV node before it passes through the bundle of hiss and the pereni fibers of the left and right ventricles causing them to contract as well on an electrocardiogram the P wave corresponds to the atrial contraction the PR interval corresponds to the slight delay through the AV node and the QRS complex is ventricular contraction now in a normal electrical conduction system the AV node is the only place place where the signal can get through from the Atria to the ventricles it's kind of like there's this gatekeeper that has to stop the signal to make sure everything's good before letting it pass so there's always a slight delay here people with wpw essentially have a secret backd door entrance this entrance being secret and all doesn't have a gatekeeper and therefore has no delay as a signal moves through it this secret back door entrance is a tiny bundle of cardiac tissue that conducts electrical signals really well and it's called the bundle of Kent using the bundle of Kent means that the ventricles start to contract a little bit early called pre-excitation if the bundle's on the left side of the heart it's called type A preexcitation if it's on the right side it's called type B preexcitation although type A on the left side is a lot more common all right even though that signal sneaks through early the signal waiting at the AV node eventually makes its way through and the two signals essentially combine to contract the ventricles so on an ECG people with wpw have a short PR interval with a Delta wave as well as QRS prolongation which makes sense because the signal is taking the shortcut and Contracting the ventricles early which means that the PR interval is shorter and the overall QRS complex is longer people at wpw usually have a PR interval less than 120 milliseconds and a QRS complex greater than 110 milliseconds also the ST segment and t-wave which represents re polarization will often be directed opposite the QRS complex this wpw pattern doesn't typically cause any symptoms and it's relatively benign in some cases though this pattern can facilitate certain arrhythmias or basically make certain arhythmia more severe and potentially even cause sudden cardiac death in which case it'd be called wolf Parkinson White syndrome for example people with atrial arrhythmias might have atrial rates in the 200 to 300 beats per minute range normally the AV node doesn't allow all of these signals through and so the ventricles will contract at a lower number like for every three atrial beats there's only one ventricular beat so for 300 beats per minute in the atrium The ventricle might be going at 100 beats per minute for people with a bundle of Kent though those signals aren't held up at the AV node and the ventricles contract at the same rate as the atrium in this case at 300 beats per minute which is way too fast for the ventricles and this can quickly lead to cardiogenic shock since the heart doesn't even have time to fill with blood before each contraction and so it's barely pumping any blood in other cases the extra pathway can set up a re-entry circuit in the case of a re-entry circuit the signal might move back up the accessory pathway since the majority of these bundles of Kent are actually bidirectional meaning the signal can go from The Atrium to The ventricle as well as from The ventricle to The Atrium so an example of this would be if an electrical signal goes down the AV node goes through the ventricles and then goes back up the bundle of Kent causing the Atria to contract and then it goes back down the AV node contracts the ventricles again and goes back up the bundle of Kent creating a re-entry circuit this type where it goes from The ventricle to The Atrium is called atrioventricular re-entrant tardia or avrt with orthodromic conduction and can lead to very high ventricular rates between 200 and 300 beats per minute less commonly the signal can move in the opposite direction called avrt with antidromic conduction these circuits can be initiated by several mechanisms like premature contractions in the Atria or the ventricles it's estimated that about 1 in 1,000 people have wolf Parkinson White pattern which is congenital and present at birth a small proportion of this already small proportion go on to have the symptoms that we just discussed if they do develop dangerous Tachi arhythmia though they might be treated pharmacologically but a definitive treatment is radio frequency catheter ablation of the accessory pathway or the bundle of Kent this treatment essentially uses cautery to cut and Destroy This pathway essentially boarding off the secret back door leaving only one connection between the Atria and the ventricles the AV node thanks for watching you can help support us by donating on patreon or subscribing to our Channel or telling your friends about us on social media that