Tachycardias

Broad Complex Tachycardia

The normal upper width limit for a QRS complex is 0.11 seconds. In a tachycardia with a wide QRS complex, the diagnosis is usually that of a ventricular tachycardia (VT) but supraventricular tachycardia (SVT) with bundle branch block or accessory or aberrant conduction should also be considered. An example of broad complex tachycardia is shown in Figure RS.12. If a diagnosis cannot be made and there is a pulse follow the guidelines given in Figure RS.7.

DIFFERENTIAL DIAGNOSIS OF SVT & VT BY TREATMENT

Consider previous history

Study previous ECGs. If similar broad complex QRS morphology is seen in association with sinus rhythm this indicates a supraventricular rhythm

Obtain a current ECG to exclude VT

The default position however is that broad complex tachycardias should be treated as if they were VT (see algorithm Figure RS.8)

Figure RS.7

It may be very difficult to distinguish between the diagnoses of SVT and VT. The following guidelines have been suggested (Wellens 1978):

• Give adenosine. This will be effective in abolishing SVT but not VT

• Seek cardiological help

• Use synchronised DC cardioversion (SVT and VT)

• Do not use verapamil which is a myocardial depressant and potent vasodilator

In broad complex tachycardia, which is diagnosed as sustained ventricular tachycardia, oxygen should be administered and IV access secured. If the pulse is absent, follow the protocol for VF. If a pulse is palpable but haemodynamic stability is poor or deteriorating rapidly, help should be sought and synchronised DC cardioversion should be performed. If cardioversion is not successful, lidocaine should be given and hypokalaemia (< 3.6 mmol/l) treated. DC cardioversion can then be repeated. Other antiarrhythmics (particularly amiodarone) and overdrive pacing can be considered.

Narrow Complex Tachycardia

Narrow complex tachycardia is almost always supraventricular in origin and includes atrial flutter and fibrillation, atrio-ventricular junctional tachycardia, multifocal atrial tachycardia and paroxysmal reentrant tachycardia. In the context of the peri-arrest situation, paroxysmal supraventricular tachycardia and atrial fibrillation with a fast ventricular rate are the commonest problems. Supraventricular tachycardia can be relatively benign but may be life threatening. The algorithm for narrow complex tachycardia is shown in Figure RS.9.

Unilateral carotid sinus massage can be used to slow a paroxysmal supraventricular tachycardia but care must be taken as an increase in vagal tone in those with acute ischaemia or possible digoxin toxicity, may precipitate ventricular fibrillation. Adenosine is now established as the preferred treatment for supraventricular tachycardia both in terminating the rhythm and as a diagnostic aid. Atrial fibrillation or flutter may also be revealed because of the transient atrioventricular nodal block that occurs. If adenosine has no effect or fast atrial fibrillation exists, seek help and follow the algorithm. If time allows, drug treatment is the preferred method and local protocols as well as knowledge of indications and side effects may guide the choice of either digoxin, amiodarone, verapamil or esmolol. If adverse signs exist, then more urgent treatment is required in the form of synchronised DC cardioversion after prior analgesia or anaesthesia. DC cardioversion is also the treatment of choice in atrial flutter (whether or not there is haemodynamic compromise) and low energy shocks may be sufficient. Atrial fibrillation is treated as in the algorithms for narrow complex tachycardia, according to the ventricular rate and degree of haemodynamic problems; synchronised cardioversion is probably the most suitable treatment following myocardial infarction or severe ischaemia. Caution is required if digoxin toxicity is suspected as there may be a risk of inducing a malignant arrhythmia. In the less urgent situation digoxin can be given providing the patient is not already taking this drug, and the electrolytes are normal. Alternatively, verapamil or a beta blocker may be used to slow the ventricular rate but either of these can cause hypotension and heart failure. If atrial fibrillation was pre-existing and sinus rhythm is then restored, anticoagulation should be considered.

Cardiac Output Tachycardia

Figure RS.8

Algorithm for treatment of broad complex tachycardia © ERC 96

Malignant Neuropathy

Figure RS.9

Algorithm for treatment of narrow complex tachycardia © ERC 96

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