Ventricular tachycardia (VT) is confirmed by five or more ventricular ectopics in succession and it is usually accompanied by a sudden onset of signs and symptoms. If this rhythm occurs post myocardial infarction it can degenerate into ventricular fibrillation (VF). Ventricular tachycardia can be triggered by an irritable site within the ventricles; conduction takes place across ventricular cells, rather than along the normal specialised conducting pathway, resulting in the broad shape of the complexes. A broad complex suggests that it originates in the ventricles, particularly if the QRS complex exceeds 0.16sec.
• Ischaemic heart disease (IHD) and myocardial infarction
• Hypertrophic obstructive cardiomyopathy
• Electrolyte disturbances
• Drug toxicity or use of recreational drugs such as cocaine
• Mechanical stimulation from pacing wire or invasive line
Characteristic features of the ECG (Figure 8.3)
• P wave may be present in some leads and not in others.
• QRS rate between 150 and 300/min.
• QRS rhythm may be regular or almost regular, unless fusion beats present.
• Presence of atrioventricular dissociation (Edhouse & Morris 2002a).
• There is concordance across the chest leads, meaning that all QRS complexes are either positively or negatively orientated.
Most patients will present with symptoms associated with coronary artery disease or haemodynamic instability due to poor tissue perfusion. Symptoms may include palpitations, chest pain, profuse sweating and anxiety. The patient may lose consciousness due to a reduced cardiac output.
• If the patient is tolerating the rhythm, seek expert assistance and attempt emergency cardioversion if response to drugs is unsuccessful (European Resuscitation Council (ERC) 2001).
• If no signs of life, follow the advanced life support algorithm for VF and pulseless VT (see Chapter 6).
• VT can be self-terminating or 'non-sustained' when it returns to a normal rhythm within 30 seconds.
• In regular or monomorphic VT, the most common form of this arrhythmia, the appearance between beats is the same.
• In irregular or polymorphic VT (torsade de pointes tachycardia), there is wide beat-to-beat variation in the QRS morphology rotating every 5-20 beats along the baseline (Spearritt 2003). Torsade de pointes represents an uncommon variant form of VT which may deteriorate into VF. It may occur after a myocardial infarction or be associated with prolonged repolarisation known as QT syndromes. IHD, hypomagnesaemia, antiarrhythmics, antibacterials and bradycardia due to sick sinus syndrome precipitate torsade des pointes (Edhouse & Morris 2002b). Treatment involves alleviating any predisposing cause, improving electrolyte imbalance and overdrive pacing (Bennett 2002, Resuscitation Council UK 2000).
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