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)
-VT is the commonest cause of broad complex tachycardia
VT/Torsade de pointes- palpitations and syncope. Torsade de pointes usually terminates spontaneously but can degenerate to VF.
Unstable VT/VF- patient is pulseless and becomes rapidly unconscious, and respiration ceases (cardiac arrest)
-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
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.
Ventricular fibrillation– rapid and irregular QRS complexes
-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
-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.
-Survivors of VF without an identifiable reversible cause
-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
-faulty ICD may fire constantly or inappropriately = medical emergency, may trigger life-threatening arrhythmias
-infection, haematoma, bleeding from wound site
-Survivors of VF are, in the absence of an identifiable irreversible cause, at a high risk of sudden death.