Unusual dysrhythmias

Also known as: Dysrhythmias NOS

Related conditions: Pre-excitation tachycardia = WPW, heart blocks: 1st degree, 2nd degree and 3rd degree, Brugada syndrome and catecholaminergic polymorphic ventricular tachycardia

1. Description of the problem

The differential diagnosis of a wide complex tachycardia (QRS greater than .12 sec) includes ventricular tachycardia and ventricular fibrillation, supraventricular tachycardia with aberrancy, pre-excitation tachycardia = Wolf-Parkinson-White (WPW), and ventricular paced rhythm. An irregular wide-complex tachycardia may be atrial fibrillation with aberrancy, pre-excited (WPW) atrial fibrillation or polymorphic ventricular tachycardia/torsades de pointes.

This chapter will discuss pre-excitation tachycardia = WPW; others will be dealt with in respective chapters. The key to WPW is recognition on presentation, as treatment for common arrhythmias will cause potential morbidity in a patient with a pre-excitation arrhythmia. These patients are at risk for sudden death and should be identified when they present for other diseases.

Heart blocks can be divided into 1st degree, 2nd degree and 3rd degree. Extreme caution with 3rd-degree AV block.

Brugada syndrome and catecholaminergic polymorphic ventricular tachycardia are genetic diseases that are unusual causes of relatively common arrhythmias in older patients. These syndromes usually present in younger patients before the usual age of risk for coronary artery disease and related arrhythmias.

Clinical features

In the patient with WPW who presents with tachycardia, caution must be taken in treatment. During arrhythmias patients may present with palpitations, dizziness, shortness of breath and possibly syncope.

Patients with heart block may be asymptomatic or have syncope, dizziness, chest pain or shortness of breath.

Brugada syndrome is characterized by syncope and sudden cardiac death in otherwise healthy young males. Sudden cardiac death is due to Vfib and mostly occurs at night.

Catecholaminergic polymorphic ventricular tachycardia (Vtach) present with VT, syncope or sudden cardiac death following physical or emotional stress. First presentation usually occurs during childhood or adolescence.

2. Emergency Management

Synchronized cardioversion for unstable WPW whether regular or atrial fibrillation. Caution with any drugs, consult expert help.

Transcutaneous pacing may be necessary for 2nd- (not commonly) and 3rd-degree AV block (complete AV dissociation); can be a true emergency. Consult expert help for placement of transvenous pacing wire.

Emergency management of Brugada syndrome and catecholinergic Vtach) will be treated as outlined in algorithms presented in the ventricular tachycardia and ventricular fibrillation chapter.

3. Diagnosis

Diagnostic criteria and tests

WPW EKG findings include short PR interval and prolonged QRS with a delta wave. A delta wave is a slurred upstroke in the QRS complex that is associated with a short PR interval. Presence of a delta wave is a a great clue to diagnosis (Figure 1).

1st-degree AV block is diagnosed by prolonged PR interval (greater than 200 ms) on EKG. 2nd-degree AV block is split into type 1 and type 2. Type 1 Wenckebach is progressive PR interval increase until nonconducted AV pulse. Type 2 AV block, PR interval is constant before the nonconducted beat. 3rd-degree AV block is represented by complete dyssynchrony of atrial and ventricular pulses.

Brugada syndrome (Figure 2): EKG with type 1 having j-point elevation in V1-V3, often associated with a RBBB pattern and type II with a saddleback deformity of the ST segments in V1-V3. In Brugada syndrome genetic testing is recommended to support the clinical diagnosis. Patients with syncope and spontaneous Brugada EKG pattern are at higher risk for sudden cardiac death.

In catecholaminergic Vtach the baseline EKG may be unremarkable except for prominent U waves. Most typical rhythm seen is Vtach, but supraventricular tachycardias can occur.

4. Specific Treatment

Pre-excitation tachycardias pharmacologically can be treated with amiodarone, procainamide or sotalol. Expert consultation is advised. AV nodal blocking agents such as calcium channel blockers, beta blockers, digoxin and adenosine should not be used in pre-excitation WPW as they can initiate rapid afib. If the patient is already in atrial fibrillation and atrial flutter these drugs may accelerate the rhythm. Patients with pre-excited arrythmias and atrial fibrillation will need synchronized cardioversion at 100J. Definitive treatment of WPW syndrome is destruction of the abnormal electrical pathway by radiofrequency catheter ablation.

First-degree degree AV blocks will most likely not need treatment. 2nd-degree, especially type 2, may and third-degree AV block will need electrophysiology help; transcutaneous pacing can be used while expert help is sought.

Therapy for Brugada syndrome will depend upon the type of arrythmia, Vfib or Vtach. Follow guidelines as in Vtach and Vfib chapter.

In Brugada syndrome clinicians should avoid drugs that induce Brugada-like EKG patterns, which include flecainide and other Na+ channel blockers, verapamil, nifedipine, dlitiazem, nitroglycerin, tricyclic antidepressants and fluoxetine. Risk stratification may be needed for possible ICD placement.

Catecholaminergic polymorphic Vtach acutely should be treated as other polymorphic Vtach described elsewhere. Consult expert help; if unstable, defibrillate. Beta blockers or verapamil may be used for chronic suppression, as well as placement of an ICD.

Drugs and dosages

Procainamide can be used for WPW in a dose of 20 to 50 mg/min until arrhythmia is suppressed, hypotension, QRS prolonged by 50%, or total dose of 17 mg/kg. Side effects are bradycardia, hypotension, torsades de pointes. Avoid with QT prolongation and CHF.

Amiodarone can be used in WPW. Dose for Vfib is 300 mg iv, second dose 150 mg. For Vtach the dose is 150 mg iv and repeat if necessary. Start infusion at 1 mg/min for six hours then 0.5 mg/min for six hours. Side effects are bradycardia, hypotension and phlebitis.

Sotalol can be used in WPW. Dose is 1.5 mg/kg over five minutes. Side effects are bradycardia, hypotension, torsades de pointes. Avoid in patients with prolonged QT and CHF.

5. Disease monitoring, follow-up and disposition

If initial therapy has not worked or has worsened the situation, get expert help. These are not common problems that should be dealt with by all clinicians.

Pathophysiology

WPW is a pre-excitation pathway to the ventricles via the bundle of Kent. This accessory pathway is an abnormal electrical communication from the atria to the ventricles. The pathway does not have the same rate-slowing effect as the AV node. The accessory bundle may conduct electrical activity at a much faster rate, which can lead to hemodynamic instability and death.

1st-degree heart block occurs when impulses move slowly through the AV node. 1st-degree heart block can be caused or exacerbated by drugs such as digitalis that slow AV nodal conduction. It can be found also in healthy athletes. 2nd-degree AV block occurs when some impulses are not conducted via the AV node. Type 1 is not too serious. Type 2 is less common but more serious. 3rd-degree block is complete heart block often caused by coronary artery disease ar a side effect from drug toxicity. Other causes of all AV blocks include idiopathic fibrosis, ischemia, AV nodal disease, cardiac surgery, inflammation, infiltration and rheumatic fever.

Mutations in the SCN5A gene that encodes for the alpha subunit of the cardiac sodium channel account for 18-30% of cases of Brugada syndrome. Sudden cardiac death occurs mostly at night due to Vfib. Fever may incite the fatal arrhythmia.

Catecholaminergic Vtach occurs from mutations in ryanodine release or calsequestrin.

Epidemiology

WPW occurs in .15-.2% of people, more frequently in males than females. 60-70% are otherwise healthy without structural heart disease. It can occur with congenital anomalies such as Ebstein’s anomaly, ASD, IHSS and MV prolapse. Frequency of tachyarrhythmias is 10-40% of patients.

Brugada syndrome and catecholaminergic polymorphic Vtach are relatively rare and lethal inherited arrhythmogenic diseases.

Prognosis

In WPW risk stratification may be done by an electrophysiologist to determine likelihood of sudden cardiac death. Brugada and catecholaminergic polymorphic Vtach can have variable outcomes; in some arrhythmias can be difficult to control.

What's the evidence?

Rosner. “Electrocardiography in the patient with WPW: diagnostic and initial therapeutic issues”. Am J Emerg Med. vol. 17. 1999. pp. 705-14.

Neumar, R. “Part 8: Adult Advanced Cardiovascular Life Support: 2010 American Heart Association Guidelines for Cardiopulmonary Resuscitation and Emergency Cardiovascular Care”. Circulation. vol. 122. 2010. pp. s729-s767.

Pellegrini, C. “Clinical management of ventricular tachycardia”. Curr Probl Cardiol. vol. 35. 2010. pp. 453-504.

Munger, T. “A population study of the natural history of WPW syndrome in Olmstead County, Minnesota, 1953-1989”. Circulation. vol. 87. 1993. pp. 866-73.

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