Irregular Broad Complex Tachycardia: Differential Diagnosis and Management
| Arrhythmia | Comment | Management |
|---|---|---|
Atrial fibrillation with bundle branch block Polymorphic ventricular tachycardia With preceding QT prolongation (torsade de pointes) | Difference between maximum and minimum instantaneous heart rates, calculated from the shortest and longest RR intervals is usually >30/min, with QRS showing typical LBBB or RBBB morphology Usually due to therapy with antiarrhythmic and other drugs which prolong the QT interval (e.g. amiodarone, sotalol, erythromycin, psychotropic drugs), especially in patients with hypokalaemia and/or bradycardia Rarely congenital long QT syndrome (possible family history) | DC cardioversion (Chapter 121) if there is haemodynamic instability or other measures are ineffective In stable patient, DC cardioversion or antiarrhythmic therapy (see Chapter 43) DC cardioversion if there is haemodynamic instability or other measures are ineffective Stop drugs which may prolong QT interval Correct hypokalaemia (target potassium 4.5–5 mmol/l) If there is bradycardia/AV block, use temporary pacing at 90/min (Chapter 119 p. 673) |
| Also advanced conduction system disease with block | If due to long QT syndrome, give magnesium sulfate 2 g IV bolus over 2–3 min, repeated if necessary, and followed by an infusion of 2–8 mg/minRefer to a cardiologist | |
| Without preceding QT prolongation | Usually due to myocardial ischaemia in the setting of acute coronary syndrome | DC cardioversion if there is haemodynamic instability or other measures are ineffective |
| Other causes include acute myocarditis, cardiomyopathies (e.g. arrhythmogenic right ventricular cardiomyopathy) and Brugada syndrome (VT/VF with RBBB and precordial ST elevation) | In stable patient, DC cardioversion or antiarrhythmic therapy with IV amiodarone or beta-blocker (Table 41.2) Manage as acute coronary syndrome (Chapters 45 and 46) with urgent coronary angiography and revascularization if ischaemia is suspected or cannot be excludedRefer to a cardiologist | |
| Pre-excitedatrial fibrillation (AF) in WPW syndrome (Figure 41.2) | AF conducted variably over accessory pathway Ventricular rate typically 200–300/min | DC cardioversion if there is haemodynamic instability or other measures are ineffective |
| QRS morphology shows beat to beat variation in degree of pre-excitation | In stable patient, DC in cardioversion or antiarrhythmic therapy with flecainide or amiodarone (Tables 41.2 and 41.3)Refer to a cardiologist | |
| Pseudoventricular tachycardia(Figure41.2) | Caused by skin-electrode contact (‘toothbrush tachycardia’) | No action needed The importance of recognition is to prevent misdiagnosis as VT |
| No haemodynamic change during apparent ventricular arrhythmia | ||
| AV, atrioventricular; LBBB, left bundle branch block; RBBB, right bundle branch block; VF, ventricular fibrillation; VT, ventricular tachycardia; WPW, Wolff-Parkinson-White. | ||