Pre-excitation syndrome Microchapters
Pre-excitation syndrome is a condition in which the ventricles of heart depolarize earlier than expected via some accessory pathway conduction, leading to a premature contraction. Normally, atria and ventricles are interconnected with each other via the AV node (atrioventricular node). However, in all the pre-excitation syndromes, an accessory pathway is present that conducts impulses to ventricles besides the AV node. The accessory pathway passes the electrical impulses to the ventricles before the normal impulse of depolarization passes through the AV node. The phenomenon of depolarizing ventricles through the accessory pathway earlier than the usual depolarization is supposed to happen through the AV node is referred to as "Pre- Excitation". WPW syndrome was described in 1930 and named after John Parkinson, Paul Dudley White, and Louis Wolff. The accessory pathways are named depending upon the regions of atria and ventricles they are connecting such as Bundle of His, Mahaim fibers, and James fibers. The typical ECG findings associated with WPW syndrome are shortened PR interval, widened QRS complex and Delta wave which is a slurring in the upstroke of QRS complex due to preexcitation of ventricles via the accessory pathway. ECG findings along with symptomatic tachyarrhythmias are referred to as Wolff-Parkinson-White syndrome. Although it is more common in adults, males have an incidence rate of 0.1-0.3 %, WPW can be considered as a congenital anomaly in some cases where it is usually present since the birth and in others, it is considered as a developmental anomaly. Studies have proven its lower prevalence in children aged between 6-13 than those in the age group of 14-15 years of age. Hemodynamically unstable patients should be managed with a direct cardioversion. For the stable patients, medical management should be used first before using acceptable options of catheter ablation or surgical intervention. Although catheter ablation has widely replaced the surgical option, as it is a less invasive technique with better outcomes, in cases where catheter ablation cannot be done or doesn't prove to be effective, the surgical option is worth considering with a curative rate of nearly 100%.
- In 1915, Frank Norman Wilson became the first to describe the condition which was later referred to as Wolff–Parkinson–White syndrome.
- In 1930, WPW syndrome was first described and named after John Parkinson, Paul Dudley White, and Louis Wolff. They successfully interpreted a series of 11 healthy young patients who had repeated attacks of tachycardia in the presence of short PR interval and bundle branch block pattern on the ECG findings. They also found the association of WPW with increasing the risk of sudden cardiac death.
- British physiologist "Albert Frank Stanley Kent" (1863 - 1958), first described the lateral branches of AV grove of the monkey heart, which were later named as the accessory bundle of Kent.
- Based on the conduction pathway or fiber subtype, pre-excitation syndrome may be classified into the following sub-types:
|Type||Conduction pathway||QRS interval||PR interval||Delta wave|
|Wolff-Parkinson-White syndrome||Bundle of Kent||Wide/long||Usually short||Yes|
|Lown-Ganong-Levine syndrome||"James bundle" (atria to bundle of His)||Normal/Unaffected||Short||No|
|Mahaim-type Pre-excitation||Mahaim fibers||Long||Normal||No|
- Based on their conduction properties, following three types of accessory pathways are there:
- Manifest Accessory Pathways:
- Concealed Accessory Pathways:
- Latent Accessory Pathways:
Normal electrical conduction pathway of heart
- Normally, the electrical activity of the heart starts from SA node.
- The impulse generation usually happens in the right atrium near the entrance of superior vena cava and it travels from SA node to the AV node.
- The AV node modulates the rate and number of impulses to be conducted to the ventricles. It also modulates the speed of transmission from atria to ventricles which represents the PR interval on ECG.
- From the AV node, an electrical impulse is transmitted to the bundle of His, to left and right branches extending to the ventricular myocardium.
- WPW is another word for pre-excitation of the ventricle through the accessory pathway instead of going through the usual pathway of AV node which usually slows down the speed of conduction of impulses transmitted to the ventricles.
- The accessory pathway creates a channel directly to conduct the impulses to ventricles resulting in a premature excitation.
- In "Type A Pre-excitation", the accessory pathway lies between left atria and ventricles whereas in Type B Pre-excitation, fibers carry impulses between right atria and ventricles.
- Basic concept of pathophysiology in pre-excitation syndrome lies in the concept of bypassing the AV node conduction and letting the impulse conduct faster through atria to ventricles via accessory pathways.
- These accessory pathways usually known as Bundle of Kent in WPW syndrome, James fiber in LGL syndrome, and Mahaim fibers in Mahaim type pre-excitation syndrome.
- These conduct impulses in forward (not common), backward (around 15-20%), and in both directions (most common type) as well.
- The accessory pathways mediate the occurrence of tachyarrhythmia by forming a re-entry circuit and commonly known as AVRT.
- The direct conduction of impulses from atria to ventricles can also result in the development of tachyarrhythmias when there is a development of atrial fibrillation with RVR.
- WPW syndrome is a combination of WPW pattern on ECG plus paroxysmal arrhythmias.
- The accessory pathways are usually named as Bundle of Kent or AV bypass tracts.
- The accessory pathways here are named as James fibers, also known as atrionodal fibers connecting the atrium to the distal AV node.
- These usually conduct the impulses from atria to the initial portion of the AV node.
- The accessory pathways named as Mahaim fibers connect the Atrium, AV node, or bundle of His to the Purkinje fibers or ventricular myocardium.
Differentiating Pre-excitation Syndrome from other Diseases
Epidemiology and Demographics
- WPW is commonly found with an incidence of around 0.1-3.0 per thousand population.
- More common in the male population as compared to females.
- Familial studies have found that it is 0.55% more commonly found amoung first degree relatives.
- More common in young and healthy individuals, and as the age advances, the prevalence of disease decreases because of loss of pre-excitation.
- WPW can be considered as a congenital anomaly in some cases where it is usually present since birth whereas in others, it is regarded as a developmental anomaly. Studies have shown a lower prevalence in children aged between 6-13 than those in the age group of 14-15 years of age.
- High-risk population for development of atrial fibrillation or sudden cardiac death include:
Natural History, Complications, and Prognosis
- Numerous studies have been published to describe the natural history or disease course of pre-excitation syndrome. Data from a recent study- "Long term natural history of patients with WPW treated with or without catheter ablation" showed promising results in explaining the reduced long-term mortality rates in WPW patients who are matched for age and gender. It also explained that there is a lower mortality rate among catheter ablated patients as compared to the non-ablated ones. Although the patients can die with sudden cardiac death, death is uncommon.
- Most common complications studied in patients having accessory pathway conduction are arrhythmias and sudden cardiac death.
- If there is a development of atrial fibrillation or flutter, then there is fast conduction across the tracts which leads to an increased risk of dangerous ventricular arrhythmias.
- AV nodal blocking agents may also be the factor responsible for the increased conduction through accessory pathways causing life-threatening ventricular arrhythmias or hemodynamic instability resulting in a worse prognosis.
- Sudden cardiac death:
- Sudden cardiac death is a more common complication in patients with the following characteristics:
- The studies proved the risk of sudden cardiac death related to the pre-excitation syndrome is around 1.5% in childhood with the highest risk in the first two decades of life.
- Prognosis is usually very good if the patient is being managed and treated appropriately.
- Catheter ablation showed promising results in the curative treatment of patients suffering from this disorder.
- Sudden cardiac death is rarely seen in patients with this syndrome but when it happens, it is most commonly related to arrhythmias.
- The most common misconception about the prognosis of WPW syndrome is related to the severity of symptoms in a patient but the most important determinant of prognosis is dependent on the electrophysiologic properties of the accessory pathways.
- The conduction through accessory pathways usually decreases with age. This is due to fibrotic changes that happen with time.
- WPW syndrome is a combination of WPW pattern on ECG and paroxysmal arrhythmias. The accessory pathways are usually named as Bundle of Kent or AV bypass tracts.
- ECG features of WPW syndrome are:
- Short PR interval <120 ms (<0.12 seconds) with normal P wave morphology
- Widened QRS complex (>0.12 seconds)
- Delta wave - slurring upstroke of the initial QRS complex due to the early and rapid depolarization of ventricles (the most important criteria for the diagnosis of WPW syndrome).
- Deflection of T waves opposite to the direction of QRS complexes/secondary changes in ST-segment and T wave
- Types of AVRT varies depending on the direction of the impulse conduction in the re-entry circuit (orthodromic or antidromic):
- Orthodromic AVRT means the antegrade conduction is through the AV node and retrograde through the accessory pathway. It presents with narrow QRS complexes on ECG.
- Antidromic AVRT means the antegrade conduction is through the AP and retrograde conduction through AV node. It presents with wide QRS complexes on ECG.
- So in short, the Orthodromic AVRT preexcitation syndrome presents with narrow complex tachycardia and Antidromic AVRT pre-excitation syndrome presents with wide complex tachycardia.
- AF with RVR can be diagnosed in patients with WPW by comparing it with the baseline ECG. Look for comparison between pre-excited QRS complexes on the baseline ECG vs those seen during irregular tachycardia.
- Mainly categorized into 2 subtypes
Lown-Ganong-Levine (LGL) Syndrome
- The accessory pathways LGL syndrome are named as James fibers, also known as atrionodal fibers connecting the atrium to the distal AV node. These usually conduct the impulses from atria to the initial portion of the AV node.
- ECG features:
- The accessory pathways named as Mahaim fibers connect the atrium, AV node, or bundle of His to the Purkinje fibers or ventricular myocardium.
- ECG findings are usually normal.
History and Symptoms
- Patients with pre-excitation syndromes maybe asymptomatic, however, they can commonly experience the following symptoms:
- HEMODYNAMICALLY UNSTABLE PATIENT -- DIRECT SYNCHRONIZED CARDIOVERSION, BIPHASIC (INITIAL 100 J, LATER ON- 200J OR 360J).
- HEMODYNAMICALLY STABLE PATIENT -- THE FOLLOWING PROTOCOL SHOULD BE FOLLOWED:
- Antiarrhythmic drug
- AV Nodal blocking agents should NOT be used
- Address the underlying cause triggering dysrhythmias which may include:
- Treated by blocking the AV nodal conduction
- Help in blocking the pathways responsible for causing dysrhythmias through the involvement of the AV node (AVRT/AVNRT).
- Vagal Maneuvers - Valsalva maneuver, immersing the face in cold water or ice water, carotid sinus massage
- IV Adenosine- very short half-life and commonly used in dose around 6-12 mg
- IV Verapamil- this is a calcium channel blocker and commonly used as 5-10 mg.
- This modality has replaced drug therapy and other surgical treatment options by showing promising results. The best results have been found when it is used in conjunction with cryoblation (commonly used for septal accessory pathways and for accessory pathways near small coronary arteries).
- This technique is used widely with best results in:
- Patients with AVRT showing symptoms of dysrhythmias
- Patients with impaired functional daily activities having no symptoms with ventricular pre-excitation
- Patients with WPW and family history of sudden cardiac death in first or second-degree relatives.
- Patients with AVRT OR A.FIB with RVR
- Patients with H/O pre-excited A.FIB
- Patients who are not willing to undergo radiofrequency ablation can be managed on medical management with the use of anti-arrhythmic. Though its role in the prevention of future episodes of arrhythmias is limited, still this is the most commonly used modality of choice.
- Class 3 Antiarrhythmics and class IC drugs are used with AV nodal blocking agents in patients with a history of atrial flutter or A.Fib.
- Sotalol and Flecainide are safe options to use in pregnancy.
- Surgical management includes the following options:
- ENDOCARDIAL SURGICAL APPROACH
- EPICARDIAL SURGICAL APPROACH
- Due to the continuing advancement in medical science, radiofrequency catheter ablation is widely used as a preferred treatment option.
- Role of the surgical approach is limited to:
- The most common preventive measures used against WPW are radiofrequency catheter ablation.
- Although the success rate for the surgical approach is 100%, still the catheter ablation is preferred as it is less invasive and associated with lower complication rates.
- General measures that help in preventing the episodes such as valsalva maneuvers should be taught to the patient so that tachycardia can be relieved during an acute episode.
- Although medicines/antiarrhythmic can help prevent recurrent episodes, this is only preferred in patients who are not the candidates for catheter ablation or surgical approach.
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