Ventricular Tachycardia & Ventricular Fibrillation

Some more heart rhythm disturbances… ❤ ❤


Ventricular tachycardia and Ventricular fibrillation

Definition: disturbances of cardiac rhythm (arrhythmias). Both VT and VF are broad complex tachycardias originating in the ventricles.

VT- distinguished from ventricular ectopics, which occur singularly. If > 3 together at rate of > 120, this constitutes VT.

VF– this is very rapid and irregular ventricular activation with no mechanical effect and hence no cardiac output.

Aetiology/ risk factors:

Causes of arrhythmias include:

Cardiac: MI, coronary artery disease, LV aneurysm, mitral valve disease, cardiomyopathy, pericarditis, myocarditis, aberrant conduction pathways.

-IHD increases the likelihood of a ventricular arrhythmia. VT and VF are usually associated with underlying heart disease.

-Post-MI, 80% of VF occurs within 12h. If it occurs > 48h, usually indicates pump failure or cardiogenic shock.

Non-cardiac: caffeine, smoking, alcohol, pneumonia, drugs (Beta-2-agonists, digoxin, L-dopa, tricyclics, doxorubicin), metabolic imbalances (K+, Ca2+, Mg2+, hypoxia, hypercapnia, metabolic acidosis, thyroid disease), and phaeochromocytoma.

Torsade the pointes is a type of VT that is caused by long QT syndrome. The QT interval (start of QRS to end of T wave) is greatly prolonged. Causes include: congenital, electrolyte disturbances (hypokalaemia, hypocalcaemia, hypomagnesaemia), drugs (e.g. tricyclic antidepressants, macrolides, antihistamines, sotalol, quinidine, amiodarone), acute myocardial ischaemia, myocarditis, bradycardia (e.g. AV block), head injury and hypothermia.

QT interval- corrected for heart rate- QTc = QT √(R-R)

Males ≤ 0.44 secs (11 small squares)

Females  ≤ 0.46 secs (11.5 small squares)

Epidemiology:

-VT is the commonest cause of broad complex tachycardia

Symptoms:

VT/Torsade de pointes- palpitations and syncope. Torsade de pointes usually terminates spontaneously but can degenerate to VF.

Signs:

Unstable VT/VF- patient is pulseless and becomes rapidly unconscious, and respiration ceases (cardiac arrest)

Investigations:

-ECG/ 24h ECG-

Ventricular tachycardia– regular broad complex tachycardia, indicating a ventricular origin for the rhythm. Rate > 100bpm, QRS duration > 120ms (> 3 small squares). May be sustained (> 30 secs) or non-sustained (< 30 secs).

-marked left axis deviation (left ventricular focus)

-fusion beats or capture beats

Image result for fusion beat ecg

Fusion beat = when a normal beat fuses with a VT complex to create an unusual complex

Capture beat = normal QRS between abnormal beats

-AV dissociation (in 25%) or 2:1 or 3:1 AV block

-positive QRS concordance in chest leads (all +ve)

These ECG features point towards VT, which can sometimes be difficult to distinguish from supraventricular tachycardia (SVT). Though SVT is usually a narrow complex tachycardia, it can present as a broad complex tachycardia because of concurrent rate-related bundle branch block.

The Brugada criteria may help differentiate SVT from VT on ECG.

A lack of response to IV adenosine would also point towards VT.

Torsade de pointes– looks like VF bit is VT on a varying axis (polymorphic). It is due to prolonged QT interval (a S/E of antiarrhythmics). There are rapid irregular sharp QRS complexes that continuously change from an upright to an inverted position.

Torsade de pointes has a characteristic morphology in which the QRS complexes “twist” around the isoelectric line.

Image result for torsades de pointes ecg

 

Ventricular fibrillation– rapid and irregular QRS complexes

Image result for ventricular fibrillation ecg

 

-FBC, U&Es, glucose, Ca2+, Mg2+, TSH, cardiac enzymes

-ABG– if evidence of pulmonary oedema, reduced consciousness level, sepsis

 

-Echo- any structural heart disease?

Cardiac catheterisation +/- electrophysiological studies may be needed

Management:

-Patient should be connected to a cardiac monitor, and a defibrillator to hand.

Stable Ventricular tachycardia:

-treat reversible causes

Acute = high-flow oxygen by facemask

Correct low K+ or Mg2+

IV amiodarone (5mg/kg over 1h, then 900mg over 24h via a central line) or IV lidocaine (rarely, 50mg over 2mins followed by infusion).

If no response or if compromised (cardiac arrest/pulseless VT)- DC shock

-Oral therapy (may be required)= amiodarone loading dose (200mg/8h PO for 7d, then 200mg/12h for 7d) followed by maintenance therapy (200mg/24h). Monitor LFTs and TFTs.

Amiodarone S/Es: corneal deposits, photosensitivity, hepatitis, pneumonitis, lung fibrosis, nightmares, raised INR (warfarin potentiation), hyper/hypothyroidism. Phlebitis may occur if peripheral line used.

→Permanent pacing can be used to override tachyarrhythmia in recurrent VT, or temporary (external) pacing may be considered if acutely resistant to drug therapy.

Implanted cardioverter-defibrillator (ICD) may help in prevention of recurrent VT.

Radiofrequency ventricular tachycardia ablation may be tried in refractory cases.

Torsade the pointes: magnesium sulphate (2g IV over 10min) +/- overdrive pacing (=pacing the heart at a higher rate than the native heart rate).

Unstable/Pulseless Ventricular fibrillation: asynchronised DC shock. If arrested, following cardiac arrest protocol (CPR + shock +/- amiodarone +/- adrenaline).

Survivors of VF, in the absence of an identifiable reversible cause, should be fitted with an ICD.

Implanted Cardioverter Defibrillator

Definition: a small device implanted subcutaneously, and connected to the heart. It recognises arrhythmias and automatically delivers a defibrillation shock to the heart. Some models can also perform pace-making functions.

Indications:

-Survivors of VF without an identifiable reversible cause

-Recurrent VT

-At risk of VT/VF e.g. Long QT syndrome

-Cardiac Resynchronisation Therapy in cardiac failure (low LVEF < 30% on optimal medical therapy), in combination with a permanent pacemaker

Complications:

-faulty ICD may fire constantly or inappropriately = medical emergency, may trigger life-threatening arrhythmias

-infection, haematoma, bleeding from wound site

Complications:

-cardiac arrest

-sudden death

Prognosis:

-Survivors of VF are, in the absence of an identifiable irreversible cause, at a high risk of sudden death.

References: Cheese & Onion, Kumar and Clarke’s
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