6th March 2024

Cardiac Arrhythmias

Arrhythmias 

Background 

Any aberration of the normal cardiac rhythm is considered a cardiac arrhythmia. This may be because of a change in rate (normal heart rate 60-100 bpm) or rhythm, in terms of regularity or frequency of either atrial and or ventricular impulses. Cardiac arrhythmia can be benign or life-threatening through haemodynamic instability. 

Normal cardiac rhythm refers to electrical activity originating from the sino-atrial (SA) node within the posterior wall of the right atrium. This spreads across the atria via internodal pathways and Bachmann’s bundle, allowing for atrial contraction. The conduction arrives at the atrio-ventricular (AV) node where it is delayed allowing for sufficient ventricular filling. It continues along the bundle of His, the left and right bundle branches; the left divides into two fascicles (anterior and posterior) and the right into one fascicle, to reach the Purkinje fibres resulting in ventricular contraction. 

Any deviation from this, such as disease of SA or AV node, accessory pathways, or ectopic pacemaker activity, will result in a cardiac arrhythmia that may manifest with symptoms of palpitations, breathlessness, syncope/presyncope or cardiac arrest. Common arrhythmias include sinus bradycardia or tachycardia, atrial fibrillation or flutter, SA or AV node disease, re-entry tachycardias, and ventricular tachycardia or fibrillation. Common causes for arrhythmia include:

• Myocardial ischaemia – hypoxia causes inappropriate depolarisation of cardiac cells affecting impulse conduction and/or formation. 
• Electrolyte abnormalities – K⁺, Mg²⁺and/or Ca²⁺ disturbance.
• Drug-induced arrhythmias including antiarrhythmic medication – this may be through influence on autonomic activity, electrolyte balance or QT interval.
• Structural causes including accessory pathways and changes secondary to heart failure.

We can assess arrhythmias by detecting the electrical impulses which translate to waveforms on an ECG. Persistent arrhythmias can be detected on a standard ECG, however intermittent arrhythmias require monitoring over a period using a Holter monitor, typically monitoring between 24 hours to a few days. Longer monitoring is possible by means of an implantable loop recorder. More complex arrhythmias can be investigated using electrophysiological studies.

Electrical conduction of the heart

The action potentials at each level of the conduction pathway have unique properties complementary to their function. Cardiac action potentials are differentiated by their ability for spontaneous depolarisation or pacemaker potential and the speed at which they depolarise. Pacemaker cells found at the SA and AV nodes spontaneously generate slow response action potentials. The AV node conducts at a rate of around 0.05m/s. 

In contrast, cardiac myocytes lack the same degree of automaticity; however, they depolarise at a much faster rate. Note that the His-Purkinje system has both features of automaticity and fast conduction, with a conduction velocity of around 2-4m/s, respectively. The whole conduction occurs very quickly and any delays are translated to changes on the ECG such as prolonged PR (>200ms), QT interval or QRS duration (>120ms). We will consider the cardiac action potentials in more detail as it bears relevance to the actions of antiarrhythmic medication.

Nodal action potential

The pacemaker or nodal action potential consists of 3 phases: 4, 0 and 3. Phase 4 starts at a membrane potential of around -60mV with the opening of funny (If) channels. This allows an influx of Na⁺ ions into nodal cells and spontaneous depolarisation. This is propagated by the opening of Ca2+ channels (T-type at -50mV and L-type at -40mV) to allow an influx of Ca²⁺ ions. At the same time, there is reduced efflux of K+ due to closure of K+ ion channels. 

Once a threshold (pacemaker potential) is reached, which is around -40 to -30 mV, there is an influx of Ca2+ ions through L-type channels leading to depolarisation, which constitutes phase 0. 

The nodal cell then repolarises in phase 3 through the opening of K+ channels to allow K+ efflux and the closing of L-type Ca2+ channels, decreasing Ca²⁺ influx. This achieves a membrane potential of around -60mV and the cycle restarts again with no resting potential.

Non-nodal cardiac potential

The non-nodal cardiac myocyte potential consists of 5 phases: 4, 0, 1, 2 and 3. Phase 4 is the resting membrane potential which sits at around -90mV. In a single action potential, there is rapid depolarisation in phase 0 due to the opening of fast sodium channels allowing Na + influx and closing of potassium channels to reduce K+ efflux. Once depolarised, the myocyte begins to repolarise with the opening of K+ ion channels, allowing for K+ efflux in phase 1. This is delayed at the plateau phase in 2 due to influx of Ca²⁺ via the L-type Ca²⁺ channels. Phase 3 follows with repolarisation due to an increase in K+ influx and a decrease in Ca2+ efflux through the closing of L-type Ca2+ channels, and the membrane potential returns to the threshold level (phase 4).

Antiarrhythmic Medication

The mainstay in arrhythmia management is antiarrhythmic medication. Electrical cardioversion is used where there is haemodynamic compromise or electively to return to sinus rhythm, for instance, in AF. Alternatively, electrophysiological studies may be performed to identify arrhythmias and ablate areas along the conductive pathway to eliminate the arrhythmia. 

Antiarrhythmic drugs target ion channels in cardiac myocytes and/or nodal cells to manipulate the cardiac action potential and negate arrhythmias. Since parasympathetic and sympathetic activity also influence cardiac conductivity, drugs that affect their activity can also be used. There are numerous ways to categorise antiarrhythmics but the Vaughan-Williams classification system remains the most prevalent: 

• Class I: Na⁺ Channel Blockers. They work by reducing conduction velocity at phase 0 but can also affect phase 3 of non-nodal repolarisation and thereby change the corrected QT interval. These drugs can be further subclassified by the degree to which they block Na+ channels as well as their effect on the QTc interval. All class I drugs can be used in VT, however only Ia and Ic can be used in AF/flutter and SVT, this is because Ib drugs have little influence on atrial myocytes.
  • Ia: Moderate Na blockade, QTc prolongation – e.g., Quinidine, procainamide, disopyramide. These drugs are limited by their pro-arrhythmic effects. 
  • Ib: Weak Na blockade, QTc shortening – e.g., Lidocaine and mexiletine – only used for ventricular arrhythmias. They have a greater influence on myocytes following ischaemia, so they are useful in post-MI arrhythmias.
  • Ic: Strong Na blockage, no effect on QTc – Flecainide and propafenone. They should be avoided in patients with ischaemic heart disease or structural heart disease as they are found to cause increased mortality. 
• Class II: Beta blockers – e.g., bisoprolol, metoprolol and atenolol. They reduce sympathetic influence by blocking beta-adrenoreceptors in the heart. There is reduced SA node firing and AV node conduction, which reduces rate and conduction velocity, respectively. Side effects include bradycardia, AV block, bronchospasm, fatigue, and reduced exercise tolerance due to negative chronotropy.
• Class III – K+ channel blockers – e.g., amiodarone, dronedarone, sotalol, ibutilide, dofetilide. They affect potassium efflux, thus prolonging the QT interval. Amiodarone is commonly used in clinical practice for VT, VF, AF and flutter and has additional class I, II, and IV action. Side effects include thyroid dysfunction, deranged LFTs and pulmonary fibrosis.
• Class IV – Ca²⁺ channel blocker (non-dihydropyridines) – diltiazem and verapamil. They block L-type calcium channels which reduces both rate and velocity of conduction, most effective at nodal cells. Side effects include AV block, bradycardia and reduced contractility, therefore contraindicated in heart failure.

Other antiarrhythmics include adenosine, digoxin and atropine. For MRCP part 1, you will be expected to identify an abnormal rhythm from an ECG on clinical description and select appropriate treatment options. Table 1 summarises common conditions where these medications are used. 

Table 1: Showing mode of action of common conditions in which these medications are used. 

References

• Klabunde RE. Arrhythmias. Cardiovascular Physiology Concepts. Last updated October 11th 2012. Available at https://www.cvphysiology.com/Arrhythmias/A008/
• Wei X, Yohannan S, Richards JR. Physiology, Cardiac Repolarization Dispersion and Reserve. StatPearls.  Last updated April 21st 2022. Available at https://www.ncbi.nlm.nih.gov/books/NBK537194/ 
• Klabunde RE. Vaughan-Williams Classification of Antiarrhythmic Drugs. Cardiovascular Physiology Concepts. Last updated March 19th 2010. Available at https://www.cvpharmacology.com/antiarrhy/Vaughan-Williams/
• King GS, Goyal A, Grigorova Y, et al. Antiarrhythmic Medications. StatPearls. Last updated February 16th 2022. Available at https://www.ncbi.nlm.nih.gov/books/NBK482322/ 

Bradycardias

Background 

Bradycardia is defined as a ventricular rate below 60 bpm and may be physiological in athletes or during sleep. Pathological bradycardia may be a consequence of SA node and or AV node dysfunction. In these cases, patients may present with fatigue, dizziness, syncope, vertigo, and hypotension. Causes for bradycardia include:

• Acute myocardial infarction and ischaemia
• Disease of SA node (Sick sinus syndrome)  
• AV node dysfunction
• Anorexia nervosa
• Hypothyroidism 
• Hypothermia 
• Electrolyte imbalances – hypo or hyperkalaemia.
• Raised intracranial pressure
• Increased vagal tone 
• Medications: beta blockers, digoxin, calcium channel blockers, ivabradine, lithium, clonidine.

Diagnosis

History and clinical examination are important in the initial assessment of any patient who presents with an arrhythmia. Their past medical history (e.g., Sarcoidosis causing complete heart block, a background of bipolar affective disorder requiring lithium therapy) is particularly relevant and may help reveal the underlying aetiology for the bradycardia. Observations, including temperature readings, may reveal hypothermia as the underlying culprit. Other baseline investigations include blood tests such as thyroid function, troponin in the event of accompanying chest pain or a suspicion of ischaemia, and venous blood gas to rule out acidosis.

The specific rhythm can be identified on a 12-lead ECG or through more prolonged monitoring if bradycardia is intermittent. An echocardiogram is recommended to rule out any structural causes for the underlying arrhythmia. Further imaging may be warranted, such as cardiac CT or MRI. Electrophysiology studies have a limited role in bradycardias and are usually reserved for measuring conduction delay in the His-Purkinje system in patients with suspected AV conduction abnormalities.

Management 

Reversible causes should be treated initially and further treatment guided by the underlying mechanism for the bradycardia. The specific therapies are included in their respective sections below. In certain arrhythmias e.g., sick sinus disease or 1st degree AV node block, asymptomatic patients are likely to be monitored and interventions only to be considered if symptoms – such as pre-syncope, syncope or dyspnoea from chronotropic incompetence – develop. 

In haemodynamic instability, the heart rate should be increased to promote cardiac output through pharmacological or electrical means. Atropine and or isoprenaline are typically used. Atropine, an antimuscarinic drug that reduces parasympathetic activity, while Isoprenaline is a non-selective beta adrenoreceptor agonist that targets beta receptors of the sympathetic nervous system; both influence the SA and AV to increase automaticity and conduction respectively. If this fails, temporary pacing may be achieved either transcutaneously with sedation and analgesia or transvenously if facilities are available.

Sick sinus syndrome/SA node disease

This is caused by dysfunction of the heart’s natural pacemaker and can manifest on an ECG as sinus bradycardia, SA exit block, or sinus pauses. Causes can be intrinsic or extrinsic. The most common intrinsic cause is idiopathic degenerative fibrosis of the SA node cells. Other causes include ischaemia due to right coronary artery occlusion. 

Extrinsic factors include negatively chronotropic medications such as digoxin or beta-blockers, hypothyroidism and electrolyte abnormalities. Treatment for symptomatic disease is with the implantation of a permanent pacemaker. A common manifestation of sinus node disease is termed tachy-brady syndrome. This is where an SVT such as atrial fibrillation, flutter or atrial tachycardia coincides with the presence of sick sinus disease, resulting in periods of tachycardia alongside periods of bradycardia, pauses, or escape rhythms. This is managed with pacemaker insertion.

Atrioventricular block  

This occurs due to impaired conduction between the atria and ventricles. This may be at the level of the AV node (intranodal) or within His-Purkinje system (infranodal). Causes are predominantly due to idiopathic fibrosis with increasing frequency in old age. Other causes include ischaemia, infiltration (e.g., amyloidosis, haemochromatosis), infections such as endocarditis and diphtheria, negative chronotropic and antiarrhythmic drugs. There are three types of intranodal AV blocks:

• 1st degree: prolongation of the PR interval (>200ms or 5 small squares on a standard ECG at 25mm/s)
• 2nd degree: dropped QRS complexes following non-conducted P waves. This is divided into:
  • Mobitz 1 (Wenckebach): PR interval gradually prolongs until a QRS complex is dropped.
  • Mobitz 2: characterised by a fixed block without PR prolongation; often two or three P waves precede a successfully conducted QRS complex (termed 2:1 or 3:1 block respectively).
• 3rd degree or complete block is where there is complete dissociation between the P waves and QRS complexes. Here, the P-P and R-R intervals are preserved, but the two are not associated with each other. The resulting heartbeat originates from an ectopic focus and is known as a junctional escape beat. 

In addition to the ECG changes in complete heart block, clinical examination may reveal a variable S1 due to the uncoordinated nature of atrial and ventricular contraction, resulting in changes in preload and blood flow from atria to ventricles in each cardiac cycle. Assessment of the JVP will reveal cannon a-waves caused by the atria contracting against a closed tricuspid valve. 

Management 

Those with asymptomatic first-degree blocks do not require pacemaker implantation. In the event of no reversible causes, 3rd degree block requires pacemaker implantation. Mobitz 2 blocks are treated with insertion of a pacemaker due to a high risk of progressing to complete block. Complete heart block following inferior MI is likely a result of right coronary artery disease, which typically supplies the AV node. This is likely to improve with conservative measures and if the patient is haemodynamically stable, pacemaker implantation is not required in the immediate setting.

References 

• Ginks MR, Lane DA, McGavigan AD, et al. Cardiac Arrhythmias. Oxford Textbook of Medicine. Oxford University Press. 2020 January. 3 (6th ed.): 179-218. Available at https://oxfordmedicine.com/view/10.1093/med/9780198746690.001.0001/med-9780198746690-chapter-346/ 
• Glikson M, Nielsen JC, Kronborg MB, et al. ESC Scientific Document Group. 2021 ESC Guidelines on cardiac pacing and cardiac resynchronization therapy: Developed by the Task Force on cardiac pacing and cardiac resynchronization therapy of the European Society of Cardiology (ESC) With the special contribution of the European Heart Rhythm Association (EHRA). European Heart Journal. 2021 September. 42(35): 3427–3520. Available at https://academic.oup.com/eurheartj/article/42/35/3427/6358547/ 
• Burns E, Buttner R. Sinus Node Dysfunction (Sick Sinus Syndrome). Life in the Fast Lane. Last updated December 23rd 2021. Available at https://litfl.com/sinus-node-dysfunction-sick-sinus-syndrome/
• Olshansky B, Saha S, Gopinathannair R. Bradycardia. BMJ Best Practice. Last updated November 18th 2021. Available at https://bestpractice.bmj.com/topics/en-gb/832/ 

Tachycardias

Tachycardia is defined as a ventricular rate of above 100 bpm and can arise from a primary cardiac aetiology or secondary to demand for an increased cardiac output, such as sinus tachycardia in response to hypovolaemia. Patients may complain of feeling tired, palpitations, light-headedness, shortness of breath, chest discomfort, and may arrest in certain tachyarrhythmias where output is significantly compromised e.g., VT or VF. The various tachycardia syndromes can be organised by the width of the QRS complex into narrow (QRS <0.12s) or broad (QRS >0.12s). 

Supraventricular Arrhythmias

Supraventricular tachycardias (arising from above the level of the ventricles) produce narrow QRS complexes. However, in the event of a supraventricular tachycardia in the presence of a bundle branch block or an accessory pathway (aberrancy), the QRS complex will be broad.

Atrial fibrillation (AF) 

AF is characterised by chaotic atrial activity as a result of electrical discharge from multiple foci, predominantly within the pulmonary veins that drain into the left atrium. It is commonly an accompanying feature of hypertension or ischaemic heart disease. It can also be due to structural cardiac changes e.g. valve disease, hypertrophy or dilation, as well as an infiltrative or inflammatory process. More commonly, however, AF is seen as a result of non-cardiac causes, e.g. infection, hyperthyroidism, hyponatraemia, hypokalaemia and PE. Other factors such as caffeine, alcohol and smoking may also contribute to the development of AF. AF is also strongly correlated with obstructive sleep apnoea, obesity and metabolic syndrome. It is:

• Paroxysmal: if it occurs for less than 7 days (typically less than 48 hours)
• Persistent: if it continues beyond 7 days 
• Permanent: arrhythmia is longstanding, where cardioversion has failed and when it is accepted that no further attempts will be made to cardiovert. 

Patients may be asymptomatic or report palpitations, breathlessness, and fatigue. Where there is a rapid ventricular response or underlying coronary artery disease, chest pain may develop. Very rarely, AF may present with syncope. The ECG is characterised by an absence of p waves and irregularly irregular QRS complexes due to the variation in AV node conduction of the chaotic atrial electrical activity. 

Beyond the ECG, blood tests can help to confirm infection, thyroid dysfunction and electrolyte abnormalities including sodium, potassium, calcium and magnesium. An echocardiogram can assess for an underlying structural cause such as valvular pathology (i.e. mitral stenosis or regurgitation) but also look for left atrial dilation, which can inversely correlate with the success of rhythm control / management. 

Management

This focuses on rate and/or rhythm control and anticoagulation to reduce stroke risk. NICE guidance on when rhythm control is more appropriate over rate control includes patients with new-onset AF, those with a reversible cause, AF leading to LV dysfunction, or those with flutter amenable to ablation. Rhythm control is also considered where rate control strategies have failed or symptoms persist despite adequate rate control.

Rate control involves beta blockers or rate limiting calcium channel blockers (preferential in asthmatics) as first line, or digoxin if there are concerns for LV dysfunction. In the event of an accessory pathway (i.e. pre-excited AF) then AV nodal blocking agents should be avoided as they reduce the buffering effect of the AV node and allow the atrial arrhythmia to degenerate into a ventricular arrhythmia. Therefore, in the event of pre-excited AF, class 1a, 1c and 3 antiarrhythmics are utilised, including procainamide, flecainide and amiodarone, respectively. If the onset of AF is <48 hours, rate control should be initiated, and if the rhythm does not return to the sinus within 24 hours, consideration can be made for cardioversion using flecainide if there is no underlying evidence of coronary disease or LV dysfunction. Alternatively, Amiodarone may be used. Most episodes of AF will resolve spontaneously, especially where there is an underlying cause, such as infection. In the event of haemodynamic compromise, returning to sinus rhythm is a priority using direct current cardioversion. Beyond 48 hours of onset or where the timeline is unclear, rate control and anticoagulation for at least 3 weeks with either warfarin or a DOAC is initiated in preparedness for outpatient cardioversion. Amiodarone can be given prior to cardioversion to increase the likelihood of success. 

Anticoagulation is continued for 4 weeks following cardioversion in low-risk patients. The CHA2DS2-VASc score (Table 2) is used to assess the need for long term anticoagulation.  The HAS-BLED score has been superseded by the ORBIT score in assessing bleeding risk. Scoring high encourages caution with oral anticoagulation and a review of bleeding risk factors. Catheter ablation may be used in AF but following a single procedure may return in up to 20-30% of patients.

 Table 2: CHA2DS2-VASc score determines stroke risk in patients with AF. Score of 2 or more warrants anticoagulation. A score of 1 in men warrants consideration.

Atrial Flutter

In contrast to the chaotic atrial activity of AF, flutter is characterised by a more organised arrhythmia, typically with a counter-clockwise macro reentry circuit occurring within the right atrium. This circuit is seen on the ECG as flutter waves, which have a characteristic saw-tooth pattern in V1 and negative flutter waves inferiorly (leads II, III, AVF). These waves occur at a rate of around 300/min, which is dampened by the AV node, which may result in a 2:1, 3:1, or 4:1 block giving a ventricular rate of 150, 100 or 75 bpm, respectively. In the presence of a variable block, the rhythm may be irregular. 

Management is similar to AF and the principles of thromboprophylaxis remain the same for elective cardioversions as outlined for AF. It is useful to calculate the CHA2DS2-VASc score and consider anticoagulation in those with a high score to prevent thromboembolic events, as patients may experience both flutter and fibrillation episodes.

Rate control is typically difficult to attain with atrial flutter, which tends to respond less to digoxin. Initially, a beta blocker or rate limiting calcium channel blocker may be used. Atrial flutter responds well to electrical cardioversion, requiring very low energy levels to restore sinus rhythm; but in view of stroke risk, similar recommendations as in AF are advocated with respect to three-weeks of uninterrupted anticoagulation prior to cardioversion for onset >48 hours. 

Typical atrial flutter is often successfully definitively managed with radio-frequency ablation within a localised area between the tricuspid valve annulus and the inferior vena cava (the cavo-tricuspid isthmus) which is key to the macro reentry circuit. First attempts are often 90% successful at attaining curative intent. 

Focal Atrial Tachycardia

Accelerated atrial activity arising from a focal area within the atria other than the SA node presents with a regular but abnormal p wave morphology with a rate >100/bpm. There may be some level of AV block but 1:1 AV conduction of atrial tachycardias can result in dangerous exacerbations of the ventricular rate.  

A variation of this is multifocal atrial tachycardia, most commonly seen in patients with COPD or congestive heart failure. As above, there is an accelerated atrial rhythm but there are at least three distinct p wave morphologies. The management is similar to AF with rate and rhythm control, but anticoagulation does not play a role here due to relatively organised atrial activity.

Atrioventricular nodal reentry tachycardia (AVNRT)

AVNRT occurs due to two (fast and slow) pathways within the AV node. These pathways have varying refractory periods which allow for a re-entry tachycardia to arise. The ECG will show a regular narrow complex tachycardia with no discernible p waves and pseudo-R’ waves in V1/V2, characteristic of retrograde conducted p waves.

Patients may describe transient episodes of palpitations that are well tolerated. The arrhythmia is managed by creating a temporary block in the AV node to interrupt the re-entry circuit and can be achieved by vagal manoeuvres; adenosine or verapamil if adenosine is contraindicated (e.g., asthmatic patients). Medical prophylaxis includes beta-blockers, verapamil or digoxin and curative treatment involves radiofrequency ablation. In those with refractory AVNRT Amiodarone may be used. 

Atrioventricular reentry tachycardia (AVRT)

This is less common than the AVNRT but is equally a re-entry tachycardia where there is an accessory pathway running between the ventricles and atria, distinct from the AV node. It can be difficult to discern AVNRT from AVRT, with the latter typically conducting at faster rates. Management is with AV nodal blocking agents with preference for those that work on both the AV node and the accessory pathway, such as Flecainide or Sotalol. There is good success with radiofrequency ablation as a curative option.

Wolff-Parkinson-White (WPW) 

The existence of an anterograde pathway between the atria and ventricles called the bundle of Kent, allows conduction to travel faster via the accessory pathway and normal speed through the AV node and normal conductive pathway. This causes a slurred upstroke to the QRS complex known as a delta wave and shortened PR interval. When this conduction abnormality results in tachyarrhythmia, it is termed Wolff-Parkinson-White Syndrome. 

There is a small familial link with WPW, however the condition is also associated with congenital structural cardiomyopathies such as hypertrophic cardiomyopathy or Ebstein’s anomaly (apical displacement of tricuspid valve resulting in tricuspid regurgitation and atrialisation of the basal right ventricle). It is estimated that the majority of patients with WPW pattern ECG are asymptomatic.

Treatment of haemodynamically stable WPW supraventricular tachycardias includes vagal manoeuvres and medications such as Amiodarone or Procainamide. Often, pre-excited AF in the context of WPW is poorly tolerated; however, where there is haemodynamic compromise, DCCV with sedation is appropriate. Radiofrequency ablation of the accessory pathway is the treatment of choice for patients with WPW. AV nodal blocking agents such as verapamil, diltiazem, adenosine, and digoxin should be avoided in WPW as they can increase conduction via the accessory pathway leading to a ventricular arrhythmia. 

Ventricular Arrhythmias 

As a rule, all tachycardias that are ventricular in origin will have broad QRS complexes due to the relatively slower conduction within ventricular myocardial cells. 

Ventricular Tachycardia (VT)

VT is a broad, complex tachycardia originating from the ventricles. It is sustained if it lasts more than 30s or non-sustained if it lasts between 3 beats and 30s. Risk factors for VT include structural heart disease, typically 48 hours after or even many years following acute ischaemic events and previous cardiac surgery. VT in younger patients is likely a consequence of a cardiac genetic syndrome. VT may present with cardiac arrest, syncope, chest pain and breathlessness. 

When QRS complexes are similar in morphology they are monomorphic, or polymorphic if they vary, the latter has an increased risk to progress to ventricular fibrillation. Identifying VT can be challenging and in the event of a cardiac arrest, a broad complex tachycardia should be treated as such. The following ECG features make VT more likely: 

• AV dissociation
• Capture beats 
• Fusion beats
• Very broad complex (>140ms)
• Positive/negative concordance across chest leads and extreme axis deviation. 

An important mantra to remember is that a regular broad complex tachycardia is VT until proven otherwise; if in doubt, treat any broad complex tachycardia as VT.

Management is with drug therapy including intravenous Amiodarone and Lidocaine if the patient is haemodynamically stable. In sustained VT with haemodynamic compromise, urgent DC cardioversion is warranted. Verapamil is contraindicated as it can lead to further clinical deterioration. If there is no obvious precipitating cause, consideration should be made for ICD insertion for secondary prevention. 

Torsade de pointes

This is a polymorphic VT which occurs with a prolonged QT interval (measured from start of Q wave to end of T wave). A long QT may be a result of a congenital genetic abnormality or acquired (see Table 3).  Management includes stopping the precipitating agent which may resolve the episode of torsade. IV Magnesium is administered to stabilise the cardiac membrane and where there is haemodynamic instability DCCV is used. 

 Table 3: Causes of QT prolongation. [Adapted from the Oxford Textbook of Medicine].

Ventricular Fibrillation (VF)

This describes a chaotic irregular ventricular tachyarrhythmia, with no discernibility of any wave formation. It is the most common cause of death within a few hours of a myocardial infarction, as this can precipitate an R on T phenomenon. This describes a ventricular ectopic depolarisation i.e., the R wave being superimposed on the prior repolarisation i.e., the T wave. Other than ischaemia, other causes of VF include:

• Structural disease with impaired ventricular function or severe LV hypertrophy
• Preceding VT can rapidly deteriorate to VF
• AF with aberrancy, especially in the presence AV blocking agents (adenosine, digoxin, verapamil, b-blockers)
• Metabolic states such as hypoxia and acidosis can precipitate VF 
• It is important to note that genetic syndromes can also precipitate VF, such as patients with Brugada and long-QT syndrome, such patients may subsequently receive ICD implantation

VF is not compatible with life and so requires urgent electrical cardioversion.

References

• Chhabra L, Goyal A, Benham MD. Wolff Parkinson White Syndrome. StatPearls. Last updated August 11th 2021. Available at https://www.ncbi.nlm.nih.gov/books/NBK554437/ 
• Atrial Fibrillation. Clinical Knowledge Summaries. National Institute for Health and Care Excellence (UK). Last updated January 2022. Available at https://cks.nice.org.uk/topics/atrial-fibrillation/ 
• Burns E, Buttner R. Focal Atrial Tachycardia (FAT). Life in the Fast Lane. Last updated December 19th 2021. Available at https://litfl.com/atrial-tachycardia-ecg-library/ 

Genetic Syndromes

Brugada syndrome

This predominant sodium channelopathy is autosomal dominant with the SCN5A gene affected in 20% of cases. The heart is structurally normal but patients are at risk of sudden cardiac death from VT or VF. Presentation may be with cardiac arrest or with incidental finding of typical ECG changes including coved ST elevation of at least 2 mm in at least 2 precordial leads from V1-3. ECG changes may be transient and tests such as a flecainide (Na channel blocker) challenge can be used to reveal the characteristic ST changes. 

Management 

Management is with the insertion of an ICD device.

Arrhythmogenic right ventricular cardiomyopathy (ARVC)

Patients develop fibrofatty infiltration within the right ventricle, resulting in dilation of the right ventricle. ARVC fibrofatty infiltration is not limited to the RV and can occur in the left heart as well. The condition is autosomal dominant in inheritance and, thus, there may be a family history of sudden death. The changes predispose to failure or arrhythmias which can lead to sudden cardiac death. Young patients may initially present with symptoms of palpitations, syncope, or sudden cardiac death. 

Diagnosis 

The ECG will show either T wave inversion in V1-3 and or an epsilon wave in V1, resembling a blip at the end of the QRS complex. Cardiac MRI is the imaging of choice and often shows fibrosis of the RV, regional wall motion abnormalities and pseudoaneurysmal changes. 

Management depends on risk stratification; low risk patients are started on an antiarrhythmic, typically sotalol. ICDs are implanted in patients with high-risk features (e.g., family history of sudden death or previous syncope).

Congenital Long QT Syndrome (LQTS)

These consist of numerous, mainly autosomal dominant, genetic defects encoding for ion channel proteins, which prolong ventricular repolarisation, resulting in prolongation of the QT interval (QTc >440ms in men and >460ms in women). This is achieved by reduced outflow of potassium or prolonged inflow of sodium. Prolonging of the QT interval may result in a polymorphic VT with the typical characteristic of Torsades de Pointes. This may be triggered by increased sympathetic activity such as exercise or emotional stress. There are three main genetic subtypes shown in Table 4:

Table 4: Genetic subtypes of LQTS

The long QT may be identified after the patient presents with symptoms of palpitations or syncope. The Schwartz score helps to offer the likelihood that a patient has LQTS. Beta-blockade is used in these patients and ICD is implanted in high-risk patients. It is worth mentioning that there are eponymous syndromes including ‘Jervell and Lange-Nielsen’ and ‘Romano-Ward’ with which patients have LQTS but with associated hearing loss or no-hearing loss respectively.

Catecholaminergic polymorphic ventricular tachycardia (CPVT)

Patients will have episodes of bidirectional ventricular tachycardia, clinically presenting as syncope during exercise or emotional stress. Structurally, they have normal hearts and resting ECG is also normal. There is potential for the VT to progress to VF and lead to sudden cardiac death. Approximately 30% of patients will have one episode of cardiac arrest. 

Diagnosis

Exercise testing is useful in revealing the characteristic bidirectional VT. Genetic testing can also be used, the genes affected are involved in intracellular calcium handling including the ryanodine receptor (RYR2) and calsequestrin receptor (CASQ2). Treatment is with beta-blockers to prevent syncopal episodes and consideration of ICD in high-risk individuals or those with refractory symptoms.  

References

• Ginks MR, Lane DA, McGavigan AD, et al. Cardiac Arrhythmias. Oxford Textbook of Medicine. Oxford University Press. 2020 January. 3 (6th ed.): 179-218. Available at https://oxfordmedicine.com/view/10.1093/med/9780198746690.001.0001/med-9780198746690-chapter-346/ 
• Cadogan M, Buttner R. Epsilon Wave. Life in the Fast Lane. Last updated February 4th 2022. Available at https://litfl.com/epsilon-wave-ecg-library/
• Napolitano C, Priori SG, Bloise R. Catecholaminergic Polymorphic Ventricular Tachycardia. Gene Reviews. Last updated October 13th 2016. Available at https://www.ncbi.nlm.nih.gov/books/NBK1289/