Pre-excitation disorders Notes

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Atrioventricular nodal reentrant tachycardia (AVNRT)

Wolff-Parkinson-White syndrome

NOTES NOTES PRE–EXCITATION DISORDERS GENERALLY, WHAT ARE THEY? PATHOLOGY & CAUSES ▪ Heart rhythm disturbances due to accessory pathway in conduction system that allows depolarization to bypass atrioventricular node and spread from atria to ventricles ▪ Accessory pathways can promote arrhythmias by two mechanisms ▫ Acting as one limb of a reentrant circuit, with atrioventricular node acting as the other ▫ Bypassing physiologic atrioventricular nodal delay → impulses reaching ventricle not regulated → very rapid ventricular responses in atrial arrhythmia setting such as atrial fibrillation, atrial flutter ▪ If ventricular rate becomes too high → ventricles don’t have time to fill → low cardiac output → shock SIGNS & SYMPTOMS ▪ Tachyarrhythmias → palpitations, chest discomfort, breath shortness, lightheadedness, syncope DIAGNOSIS ▪ See individual disorders TREATMENT ▪ Acute termination of preexicitationassociated arrhythmias ▪ Chronic prevention of preexicitationassociated arrhythmias MEDICATIONS ▪ Acute termination ▫ Adenosine: short acting; causes transient heart block (↓ rate of diastolic depolarization, ↓ HR) ▫ Diltiazem (Class IV): calcium channel blocker (↓ AV node conduction → ↓ HR) ▪ Chronic prevention ▫ Amiodarone (Class III): slows conduction rate (↑ AP duration, ↑ QT interval) ▫ Procainamide (Class 1A): slows conduction velocity (↑ AP duration, ↑ ventricular refractory period, ↑ QT interval) OTHER INTERVENTIONS ▪ Acute termination ▫ Vagal maneuver (carotid sinus massage/ Valsalva maneuver) → activates vagus nerve ▫ Electrical cardioversion (if pharmacological treatment ineffective/ fast heart rate is poorly tolerated) ▪ Chronic prevention ▫ Radiofrequency catheter ablation (definitive treatment) OSMOSIS.ORG 111
AV REENTRANT TACHYCARDIA (AVRT) osms.it/av-reentrant-tachycardia PATHOLOGY & CAUSES ▪ Arrhythmia due to accessory pathway between atria and ventricles that allows electrical signal to move backwards Orthodromic atrioventricular reentrant tachycardia (AVRT) ▪ Signal moves downward through atrioventricular node → ventricles contract → upward through accessory pathway → atria contract → moves back down atrioventricular node → etc. Antidromic atrioventricular reentrant tachycardia (AVRT) ▪ Signal moves downward through accessory pathway → ventricles contract → upwards through atrioventricular node → atria contract → moves back down the accessory pathway → etc. SIGNS & SYMPTOMS ▪ Tachyarrhythmias → palpitations, chest discomfort, breath shortness, lightheadedness, syncope DIAGNOSIS OTHER DIAGNOSTICS ECG ▪ Orthodromic AVRT ▫ Regular, narrow-complex tachycardia, P waves are typically retrograde in morphology and come after QRS complex ▪ Delta wave is not seen ▪ Antidromic AVRT ▫ Regular, wide-complex tachycardia, P waves often not visible 112 OSMOSIS.ORG TREATMENT MEDICATIONS ▪ Acute termination ▫ Adenosine, Diltiazem (Class III) ▪ Chronic prevention ▫ Amiodarone (Class III), Procainamide (Class 1A) OTHER INTERVENTIONS ▪ Acute termination ▫ Vagal maneuver ▫ Electrical cardioversion (if pharmacological treatment ineffective/ fast heart rate is poorly tolerated) ▪ Chronic prevention ▫ Radiofrequency catheter ablation
Chapter 16 Pre-excitation Disorders Figure 16.1 An electrocardiogram demonstrating othodromic AVRT. Note the narrow QRS complexes and absence of a discernible P wave. Figure 16.2 An ECG demonstrating orthodromic AVRT with regular, narrow-complex tachycardia with retrograde P waves visible just after the QRS complexes, most visible in leads II and V4-V6. OSMOSIS.ORG 113
Figure 16.3 An ECG demonstrating antidromic AVRT. There is a regular, wide complex tachycardia that is usually indistinguishable from VT. WOLFF–PARKINSON–WHITE SYNDROME osms.it/wolff-parkinson-white-syndrome PATHOLOGY & CAUSES ▪ Congenital accessory pathway conducts electrical signals between atria and ventricles → preexcitation, predisposes individuals to clinically significant arrhythmias up to sudden cardiac death ▫ Though “bundle of Kent” is a common eponym for congenital accessory pathway, several different pathways can occur, most commonly direct atrioventricular connections, but also atriofascicular, nodofascicular, atrioHisian, etc. ▫ Wolff–Parkinson–White pattern: benign asymptomatic form, solely described by compatible electrocardiographic changes 114 OSMOSIS.ORG ▪ Most common type of ventricular preexcitation syndrome ▫ 0.1% of individuals have Wolff– Parkinson–White pattern, a small proportion of them develops syndrome SIGNS & SYMPTOMS ▪ Tachyarrhythmias → palpitations, chest discomfort, breath shortness, lightheadedness, syncope
Chapter 16 Pre-excitation Disorders DIAGNOSIS OTHER DIAGNOSTICS ECG ▪ Short PR interval (< 120ms) ▪ Delta wave ▫ Slurred upstroke of QRS ▪ Widening of the QRS complex (> 110ms) ▪ Secondary ST segment, T wave changes TREATMENT MEDICATIONS ▪ Acute termination ▫ Adenosine, Diltiazem (Class III) ▪ Chronic prevention ▫ Amiodarone (Class III), Procainamide (Class 1A) OTHER INTERVENTIONS ▪ Acute termination ▫ Vagal maneuver ▫ Electrical cardioversion (if pharmacological treatment ineffective/ fast heart rate is poorly tolerated) ▪ Chronic prevention ▫ Radiofrequency catheter ablation Figure 16.4 ECG pattern in Wolff–Parkinson–White syndrome. OSMOSIS.ORG 115
Figure 16.5 An ECG of an individual with Wolff–Parkinson–White syndrome (sinus rhythm). Delta waves are most visible in the V leads. Figure 16.6 An ECG demonstrating “pre-excited a-fib” or atrial fibrillation in a person with Wolff–Parkinson–White. It’s an irregularly irregular wide-complex rhythm with no discernible P waves. 116 OSMOSIS.ORG

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