Ventricular tachyarrhythmias

Types:

There are 4 main types of ventricular tachyarrhythmias:

• Ventricular premature beats
• Ventricular tachycardia (VT)
• Ventricular fibrillation (VF)
• Torsades de pointes (twisting of points)

Causes of ventricular tachyarrhythmias:

All but Torsades de pointes:

• Coronary heart disease
• HT
• Cardiomyopathy

Torsades de pointes:

• Hypokalaemia/hypocalcaemia/hypomagnesaemia
• Organophosphate insecticides
• Acute MI
• Mitral valve prolapse
• Many drugs (especially antiarrhythmic agents)

Ventricular premature beats:

On the ECG:

• The premature beat has a broad (>0.12s) QRS complex because it arises from an abnormal (ectopic) site in the ventricular myocardium
• Following the premature beat, there is usually a complete compensatory pause because the AVN or ventricle is refractory to the next sinus impulse
• Early R-on-T ventricular premature beats (occurring simultaneously with the upstroke or peak of the T wave of the previous beat) may induce VF, particularly following MI

Treatment:

• Drugs from classes I, II or III are used
• In the absence of heart disease, ventricular premature beats may be safely ignored

Ventricular tachycardia:

• Defined as 3 or more ventricular beats occurring at a rate of >120bpm
• Often the patient will be hypotensive and ill (but some VTs are well tolerated)

ECG shows:

• Rapid ventricular rhythm with broad (often >0.14s) abnormal QRS complexes
• Dissociated P wave activity may be seen

Treatment:

• May be urgent depending on the haemodynamic situation
• If the cardiac output and the BP are very depressed, emergency DC cardioversion must be considered
• On the other hand, if the BP and CO are well maintained, IV therapy with class I drugs is usually advised

First-line treatment consists of:

• Lidocaine (50-100mg IV over 5 minutes)
• Followed by a lidocaine infusion (2-4mg IV per minute)

Ventricular fibrillation:

• This is very rapid and irregular ventricular activation with no mechanical effect
• The patient is pulseless and becomes rapidly unconscious and respiration ceases

ECG shows:

Shapeless, rapid oscillations and there is no hint of organized complexes

It is usually provoked by a ventricular ectopic beat (especially in acute MI), VT or torsades de pointes

Rarely reverses spontaneously

Treatment:

• The only effective treatment is electrical defibrillation or (on rare occasions) IV bretylium (5-10mg/kg over 5 minutes)
• Basic and advanced life support is needed

Torsades de pointes:

• This arrhythmia is usually short in duration and spontaneously reverts to sinus rhythm
• It does, however, give rise to presyncope or syncope and occasionally converts to VF, and sudden death may occur

ECG shows:

• Rapid, irregular sharp complexes that continuously change from an upright to an inverted position
• Between spells of tachycardia, the ECG shows a prolonged QT interval

Treatment:

• Correction of any electrolyte disturbance
• Cessation of any causative drugs
• Maintenance of the HR with atrial or ventricular pacing
• IV isoprenaline may be effective when QT prolongation is acquired
• ß-blockade or left stellectomy is advised if QT prolongation is congenital (isoprenaline is contraindicated for congenital long-QT syndrome)