Ventricular tachycardia
Ventricular tachycardia (VT, or V-tach) is a potentially life-threatening ventricular arrhythmia which is most commonly a complication of ischaemic heart disease, but it can also occur due to electrolyte disturbances (most importantly hypokalaemia), myocarditis, and prolonged QT. It’s a wide QRS complex tachycardia that’s defined as 3 or more consecutive ventricular beats at a frequency of > 100/min.
Classification
We can distinguish two types according to the duration, two types according to the morphology, and two types according to the presence of pulse:
- Classification by duration
- Nonsustained ventricular tachycardia (NSVT) – VT lasting < 30 seconds and spontaneously terminating
- Sustained ventricular tachycardia – VT lasting > 30 seconds
- Classification by morphology
- Monomorphic VT – a single arrhythmogenic focus causes all the beats to have the same morphology on ECG
- Polymorphic VT – multiple arrhythmogenic foci cause all the beats to have different morphology on ECG
- Torsade de pointes is a special form of polymorphic VT which occurs in patients with prolonged QT interval
- Classification by presence of pulse
- Pulseless VT – VT which does not produce a palpable pulse in the patient’s carotids
- VT with pulse – VT which does produce a palpable pulse
Polymorphic VT is more commonly seen with acute ischaemia, while monomorphic VT is more commonly seen with structural heart disease or myocardial scarring following infarction.
Clinical features
Ventricular tachycardia can cause symptoms like hypotension, dizziness, palpitations, and syncope. Nonsustained VT is often asymptomatic.
Treatment
Asymptomatic nonsustained VT rarely requires any specific treatment. In acute cases of wide QRS tachycardia, vagal manoeuvres should be tried. These manoeuvres do not treat VT, but they do treat SVTs with bundle branch block, which can also cause wide QRS tachycardia.
Pulseless VT is an emergency which must be handled with cardiopulmonary resuscitation (CPR) and defibrillation, as the patient has no cardiac output.
Sustained VT causing haemodynamic instability should be defibrillated or synchronised electrically cardioverted. Sustained VT not causing instability can be managed with IV amiodarone or procainamide, with cardioversion as a second option.
In all cases of VT, once the patient has stabilised, they should be evaluated for an underlying cause. VT rarely occurs in healthy hearts, and if VT is the patient’s first cardiological presentation, it’s likely that investigations like echocardiography and angiography will reveal abnormalities.
Beta blockers are important in preventing sudden cardiac death in people who’ve had symptomatic VT. Patients who’ve had symptomatic VT should also be evaluated for an ICD.