Investigations
1st investigations to order
ECG
Test
Required to establish diagnosis of ventricular tachycardia. Clinician should look for atrioventricular dissociation, fusion/capture beats, and other criteria for ventricular tachycardia.
The absence of extreme axis deviation does not imply a supraventricular origin of the tachycardia.[25]
Result
wide complex tachycardia (QRS 120 milliseconds or greater) at a rate of 100 bpm or greater; may show presence of atrioventricular dissociation, previous myocardial infarction; QRS duration: >140 milliseconds with right bundle branch block morphology, or QRS duration >160 milliseconds with left bundle branch block morphology (this does not apply to patients on anti-arrhythmic drugs); right superior axis or left bundle branch block morphology and any right axis; baseline ECG may demonstrate QT interval prolongation or evidence of Brugada syndrome or arrhythmogenic right ventricular cardiomyopathy
transthoracic echocardiogram
Test
Non-invasive test that can quickly reveal contributory and complicating mechanical and structural problems.
Result
depressed left ventricular function, wall motion abnormality, other evidence of structural heart disease, or hypertrophic cardiomyopathy
electrolytes
Test
Serves as baseline measurement and may reveal contributory factors to arrhythmia.
Result
hypokalaemia and hypomagnesaemia frequently associated with torsades de pointes
troponin I
Test
Ischaemia is a reversible cause of ventricular tachycardia and should be sought promptly to allow for revascularisation.
Result
elevated in myocardial infarction
Investigations to consider
cardiac catheterisation
Test
May be an appropriate early test for patients, especially those presenting with ventricular tachycardia/ventricular fibrillation in the setting of acute myocardial infarction.
Result
coronary artery obstruction/occlusion
cardiac MRI
Test
Particularly useful in establishing the presence of arrhythmogenic right ventricular cardiomyopathy.
Result
scar, fibro-fatty infiltration of myocardium, other evidence of infiltrative cardiomyopathy
electrophysiological (EP) study
Test
May be required to distinguish ventricular tachycardia (VT) from supraventricular tachycardia (SVT) with aberrancy in cases where the surface ECG cannot establish a diagnosis. The EP study may also be used to establish the mechanism of VT in patients with structurally normal hearts, and in patients with left ventricular ejection fraction >35% or with unexplained syncope.[28] An EP study may be helpful in such cases in determining whether or not a given patient would benefit from a prophylactic implantable cardioverter defibrillator.[7]
Result
distinguishes VT from SVT with aberrancy; establishes mechanism of VT in patients with an apparently structurally normal heart; inducible sustained monomorphic VT in patients with coronary artery disease and mild/moderate left ventricular dysfunction
genetic testing
Test
Determines underlying genetic factors associated with a number of inherited cardiovascular diseases. Consultation with a medical geneticist is recommended. Genetic counselling for the patient is essential.[16][17]
Result
mutations associated with potentially high risk of sudden death, for example, long QT syndrome, Brugada syndrome, and catecholaminergic polymorphic ventricular tachycardia
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