Arrythmias

Overview

An arrythmia refers to any disturbance in cardiac electrical activity that is not normal sinus rhythm with normal atrioventricular conduction. This may include changes in rate, rhythm or site of origin of the electrical signal for contraction. 1

Normal conduction of the heart

For the heart to pump normally2:

  1. SA node initiates an action potential spreading the current in to the right atrium (RA) and left atrium (LA) via Bachmann’s bundle
  2. SA node → AV node
  3. AV node delays conduction to ensure ventricles contract AFTER blood is emptied into the ventricles from the atria
  4. AV node → Bundle of His
  5. Bundle of His → Purkinje Fibres
  6. Purkinje fibres → cardiomyocytes (contractile cells)

Classification of Arrythmias

There are numerous types of arrythmias and can be classified as follows:

Supraventricular Arrythmias

Definition: the arrhythmia originates from above the ventricles. Therefore, as the QRS complex represents VENTRICULAR contraction, supraventricular Arrythmias have narrow aka “normal” QRS complexes.

Sinus origin

  • Originates from the SA node, therefore has a p-wave before every QRS complex.

Sinus arrythmia

Definition

Sinus arrhythmia is a normal variation of sinus rhythm. It is characterised by an irregular rhythm. More common in younger patients.3

How it works

  • Sign of health cardiovascular function
  • Resultant from physiological changes in respiration
    • Breathing stimulates the vagus nerve and changes pressures in cardiac filling
    • Vagus nerve has a role in slowing down heart rate

Clinical features

  • Usually asymptomatic

ECG features

  • P wave before every QRS
    Narrow QRS complex
    Beat-to-beat variation in P-P interval: increasing and decreasing with breathing in and out

Management

  • No management

Sinus tachycardia4

Definition: >100 bpm in adults, regular rhythm

Causes

  • Physiological: exercise, stress, pain
  • Pathophysiological
    • Compensation for reduction in stroke volume: e.g., in acute heart failure, myocardial infarction, pulmonary embolism, anaemia, sepsis
    • Increased activation of SNS: e.g., hyperthyroidism, cocaine, amphetamines

Clinical features

  • Usually asymptomatic
  • Symptomatic: palpitations, dyspnoea, light-headedness, syncope, chest pain

ECG features

  • Increased rate
  • Nil other abnormalities

Management

  • Identify and treat underlying cause. If physiologic, may not need treatment
A graph of a heart beat

AI-generated content may be incorrect.

Sinus bradycardia5

Definition: <60 bpm in adults, regular rhythm

Etiology

  • Physiological: in athletes, during sleep
  • Pathophysiological
    • E.g., Chest trauma, ischemic heart disease, vasovagal stimulation, anti-arrhythmics (e.g., digoxin, adenosine, beta blockers), hypothermia

How it works

  • changes in electrical impulse formation, conduction to AV node from SA node, or conduction through to bundle of His/Purkinje fibres.

Clinical features

  • Usually asymptomatic
  • Symptomatic: fatigue, reduced exercise tolerance, light-headedness, dizziness

ECG features

  • Reduced rate <60bpm
  • Normal sinus rhythm

Management

  • Ensure they are haemodynamically stable, ABCDE approach
  • Identify and treat underlying cause

ECG Sinus bradycardia

Figure 5: ECG showing Sinus Bradycardia

Sinus arrest6

Definition

Delay in the impulse from the SA node for 3 or more seconds, resulting in a skipped beat. Other pacemaker cells (such as those in the AV node) can produce a signal to restart normal rhythm, known as an escape rhythm. If this fails to occur → may lead to cardiac arrest. 

ECG features: absent P waves and contraction for >3 seconds

Sinus Arrest

Management

  • ABCDE and haemodynamic assessment
  • Address underlying cause
  • Holter monitoring
  • Consider pacemaker if recurrent

Re-entrant Arrythmias7

Definition

Re-entrant Arrythmias is an umbrella term for several tachyArrythmias. A re-entrant circuit refers to a self-sustaining continuous loop of electrical impulse in conductive tissue that has already been stimulated. 

For this to occur, 3 conditions must be met:

  • Two adjacent pathways with different conduction velocities and refractory periods:
    • one fast, long refractory period 
    • one other slow, short refractory period
  • Adjacent pathways must be connected proximally and distally
  • A premature action potential: If the premature action potential occurs when the fast pathway is still in refraction, this allows for a re-entrant circuit to be activated

Paroxysmal Supraventricular tachycardia (PSVT)8

Definition

Re-entrant circuit that involves the AV node. Atrioventricular nodal re-entrant tachycardia (AVNRT) and atrioventricular re-entrant tachycardia (AVRT) are subtypes with in PSVT.

Triggers

  • caffeinated drinks, stress, exercise, nicotine, hyperthyroidism, hypoxia, MI

Clinical features

  • Typical: palpitations, fatigue, anxiety, neck fullness
  • Other: dizziness, shortness of breath, nausea, chest discomfort

AVNRT vs AVRT

AVNRT9Two pathways within the AV node (one slow and fast as detailed above)

ECG features
tachycardia: often 150-250bpm
narrow QRS
P waves: not visible, or buried in, or just after the QRS complex
AVRT10Involves the AV node and an accessory (abnormal) pathway outside the AV node which a signal can go from:
Atria → ventricle (antidromic)
Ventricle → atria (orthodromic)

Wolff Parkinson White syndrome: is the most common form of AVRT in which the accessory pathway (Bundle of Kent) allows for orthodromic AVRT.

ECG features
– Short PR interval (<120ms)
Delta wave: slurring of the first portion of the QRS complex
Widened QRS complex (as a result of the delta wave)
T wave changes to opposite direction of QRS direction

https://litfl.com/pre-excitation-syndromes-ecg-library/

Management

  • If haemodynamically unstable: e.g., short of breath, hypotensive, chest pain, altered mental status, or in shock → electrical cardioversion immediately
  • If stable: first line are vagal manoeuvres: carotid sinus massage or Valsalva
    • If above does not terminate PSVT → adenosine

Atrial Flutter11

Definition: re-entrant circuit around the tricuspid valve, such that the atria are firing at 250-350 bpm. 

How it works: The AV node lacks capacity to let every signal through, creating an AV conduction ratio.

  • E.g., for every 3rd impulse from the atria, 1 goes to the ventricle (3:1 ratio)

Clinical features

  • May be asymptomatic
  • If symptomatic: palpitations, light-headedness, fatigue, dizziness, syncope, hypotension

ECG features

  • Heart rate: variable on the AV ratio.
    • If 3:1 block: usually ~100bpm
    • If 4:1 block: usually ~ 75bpm
  • Classic “sawtooth” appearance: in AV ratio

Management12

  • Often reverts with low energy, direct current electrical cardioversion
  • Often atrial flutter is insensitive to anti-arrythmics. However, if cardioversion fails, management is similar to AF (refer to AF management)

Atrial flutter with a 3-1 block

Figure 10: Image showing Atrial Flutter

Atrial Fibrillation12

Definition: numerous re-entrant circuits within the atria, such that the atria are firing at >500bpm. 

How it works: The AV node lacks capacity to let each signal through, and thus conducts signals at random to the ventricles

Clinical features

  • Palpitations, light-headedness, chest discomfort, fatigue, weakness
  • Irregular, fast pulse on palpation

ECG features

  • Tachycardic
  • Irregularly irregular rhythm
  • No p-waves
  • Occasionally, fibrillatory waves in V1: atria are shaking vigorously
Atrial Fibrillation • LITFL • ECG Library Diagnosis

Complication of AF: Increased risk of thromboembolic events (e.g., stroke)

  • Pathophysiology: increased stasis of blood within the atria → clot formation → thromboembolism
  • Assess stroke risk and bleeding risk
    • A high bleeding risk score does not necessarily mean you do not put them on anticoagulation! 
    • Unless patient has a very low stroke score or very high bleeding risk, anticoagulation therapy for thromboembolism prevention should be used. 
CHA2DS2VASc[LP1]  and HAS-BLED scoring system
CHA2DS2VASc  HAS-BLED
Congestive heart failure+1Hypertension1
Hypertension+1Abnormal renal or liver function1 or 2
Age ≥ 75+2Stroke1
Diabetes mellitus+1Bleeding1
Previous stroke, TIA or thromboembolism+2Labile INRs1
Vascular disease (PAD, prev. MI, complex aortic plaque)+1Elderly ≥ 651
Age 65-74+1Drugs or alcohol1 or 2
Sex – female+1  
Total points:
Give anticoagulant tx:
– Males: ≥2
– Females: ≥3

Consider anticoagulants
– Males: 1
– Females: 2

Not recommended:
– Males: 0
– Females: 1  
   

Anticoagulants to use: apixaban, rivaroxaban or dabigatran

Management: split into rhythm or rate control

Rhythm control: generally used for AF diagnosed <12 months, have symptoms despite rate control therapy, or reduced LVEF

  • Electrical cardioversion: direct current
  • Chemical cardioversion
    • Flecainide: acute or long term rhythm control
    • Amiodarone: acute or long term rhythm control
    • Sotalol: only for long-term rhythm control

Rate control:

  • 1st line: Beta-blockers: atenolol or metoprolol
  • 2nd line: Non-dhp CCBs: diltiazem or verapamil
  • Add-on: Digoxin
  • If LVEF <40%: amiodarone

Ectopic rhythms

Definition

Heartbeat is initiated by another part of the heart, apart from the SA node (the normal pacemaker). Consequently, extra or skipped beats may occur. This takes the form as premature atrial contraction (PAC) or premature ventricular contraction (PVC).

How it works: these ectopic signals occur prematurely, meaning, before the SA node can fire.

Clinical features

  • PAC13: mostly asymptomatic. Feeling of skipped beats or palpitations. Shortness of breath, anxiety. Irregular pulse on palpation, skipped or extra beats on auscultation
  • PVC14: mostly asymptomatic. Fatigue, palpitations, light-headedness, dizziness. Irregular pulse on palpation. 

Triggers: Stress, caffeine and alcohol, smoking, electrolyte disturbances

ECG features

Depending on the exact location of the focus, ECG changes will differ drastically. They are transient changes within an otherwise sinus rhythm.

  • PAC13
    • Normal QRS complex
    • PR interval: may be normal, short or longer than normal
    • P waves: differ in appearance to sinus P waves: may differ in length, shape, height
The ECG Educator & Mentor Blog : Premature Atrial Contraction (PAC)
  • PVC14
    • Premature QRS with abnormal morphology and >120 milliseconds
      • QRS may have LBBB or RBBB appearance depending if ectopic focus is from the right or left ventricle respectively
    • Immediately after abnormal QRS, large T-wave of opposite polarity typically occurs
    • P wave usually missing before abnormal QRS
    • Typically have a compensatory pause after the ectopic beat due to timing of refractory periods between the atria and ventricles
Premature Ventricular Contractions (PVCs) ECG Review | Learn the Heart

Management

  • Typically benign and do not require treatment.
  • PACs
    • Avoid triggers of PACs
    • If still recurrent: beta blockers
  • PVCs:
    • if recurrent and causing symptoms: beta blockers or calcium channel blockers
    • if triggering ventricular Arrythmias:
      • if currently in ventricular fibrillation: immediate defibrillation
      • consider ablation therapy

Ventricular Arrythmias

Ventricular Tachycardia (VT)15

Definition

Wide QRS complex tachycardia which originates from an ectopic focus in the ventricles. Defined as ≥3 consecutive beats at a rate of ≥100bpm. This arrhythmia can be life-threatening.

  • Sustained VT: lasting ≥30 seconds or becomes haemodynamically unstable within 30 seconds. 
  • Non-sustained: < 30 seconds in duration and stays haemodynamically stable. 

Monomorphic vs polymorphic

  • Monomorphic VT: each QRS complex, is of the same morphology. Typically due to myocardial scarring from a previous cardiac insult (e.g., myocardial scarring).
Monomorphic ventricular tachycardia VT
  • Polymorphic VT: consecutive QRS complexes are not of the same morphology. Commonly due to acute coronary syndrome
    • Torsades de Pointes: a subtype of polymorphic VT which has a classical waxing and waning pattern of QRS complexes. Long QT predisposes people developing Torsades de Pointes.
      • Causes of QT prolongation
        • Electrolyte abnormalities: hypomagnesaemia, hypokalaemia, hypocalcaeima
        • Medications/drugs: anti-arrhythmics, macrolides, olanzapine, haloperidol, TCA antidepressants
        • MI
        • Raised ICP

Polymorphic VT and Torsades de Pointes (TdP) • LITFL

Clinical features

  • Syncope, shortness of breath, cardiac arrest, cardiac death

Management

  • If in cardiac arrest: start advanced life support (ALS) pathway
  • Haemodynamically unstable: direct current cardioversion, if this fails, add IV amiodarone

Ventricular Fibrillation

Definition: wide complex tachycardia with a ventricular rate of >300 bpm. May lead to sudden cardiac death. 

Causes: sustained VT → VF, electrolyte abnormalities, acidosis, hypothermia, cardiomyopathies

How it works: VF occurs when the myocardium in the ventricles depolarise and contracts in an uncoordinated fashion.

Clinical features

  • Commonly presents as sudden collapse: no pulse, unconscious
  • Pre-event: may have chest pain, shortness of breath, nausea and vomiting

ECG features: wide complex QRS, irregular rhythm. Classical ECG of VF:

EKG Monitor Showing Ventricular Fibrillation or VF 20203441 Vector ...

Management: follow ALS pathway

Management summary table

ArrythmiaManagement
Sinus arrythmiaNone required
Sinus tachycardiaIdentify and treat underlying cause
Sinus BradycardiaEnsure they are haemodynamically stable, ABCDE approach. Identify and treat underlying cause.
Sinus ArrestABCDE and haemodynamic assessmentAddress underlying causeHolter monitoringConsider pacemaker if recurrent.
PSVTIf haemodynamically unstable → immediate electrical cardioversion.
If stable → vagal manoeuvres.
Atrial Flutter1st line: electrical cardioversion
2nd line: anti-arrhythmics (same as AF)
Atrial FibrillationConsider anticoagulants for thromboembolism prevention.
Either rhythm or rate control
– Rhythm: electrical or chemical (flecainide, amiodarone, sotalol)
– Rate: B-blockers first line
Ectopic beatsPAC:
– Avoid triggers
– If still recurrent: Beta blockers

PVC:
– If recurrent and causing symptoms: Beta blockers or calcium channel blockers
– If causing ventricular Arrythmias:
– If in VF: immediate defibrillation
– Long term management: ablation therapy
Ventricular TachycardiaIf cardiac arrest: start advanced life support (ALS) pathway.
If haemodynamically unstable:
– direct current cardioversion
– if above failed: add IV amiodarone
Ventricular FibrillationFollow ALS pathway

References

  1. Levy S, Olshansky B. Arrhythmia management for the primary care clinician. In Calkins H, Botkin NF, editors. UptoDate [Internet]. UptoDate Inc; 2024. [Updated 2024 Sep 16; cited 2025 Jun 13]. Available from: https://www.uptodate.com/contents/arrhythmia-management-for-the-primary-care-clinician?search=Arrythmias&source=search_result&selectedTitle=1~150&usage_type=default&display_rank=1#references
  2. Park DS, Fishman GI. Development and function of the cardiac conduction system in health and disease. J Cardiovasc Dev Dis. 2017;4(2):7. doi: 10.3390/jcdd4020007
  3. Soos MP, McComb D. Sinus Arrhythmia. Treasure Island (FL): StatPearls Publishing; 2025.
  4. Henning A, Krawiec C. Sinus Tachycardia. Treasure Island (FL): StatPearls Publishing; 2023.
  5. Hafeez Y, Grossman SA. Sinus Bradycardia. Treasure Island (FL): StatPearls Publishing; 2023.
  6. Dakkak W, Doukky R. Sick Sinus Syndrome. Treasure Island (FL): StatPearls Publishing; 2023.
  7. Podrid PJ. Reentry and the development of cardiac Arrythmias. In Gersh BJ, Botkin NF, editors. UptoDate [Internet]. UptoDate Inc; 2024. [Updated 2024 Mar 24; cited 2025 Jun 13]. Available from: https://www.uptodate.com/contents/reentry-and-the-development-of-cardiac-Arrythmias?search=reentry%20and%20the%20development%20of%20cardiac%20Arrythmias&source=search_result&selectedTitle=1~150&usage_type=default&display_rank=1
  8. Mitchell BL. Reentrant (Paroxysmal) supraventricular tachycardias (PSVT). MSD Manual; 2024 [Update 2024 Sep; cited 2025 Jun 13]. Available from: https://www.msdmanuals.com/professional/cardiovascular-disorders/specific-cardiac-Arrythmias/reentrant-paroxysmal-supraventricular-tachycardias-psvt?query=paroxysmal%20supraventricular%20tachycardia%20(svt,%20psvt)
  9. Knight BP. Atrioventricular nodal reentrant tachycardia (AVNRT). In Link MS, Botkin NF, editors. UptoDate [Internet]. UptoDate Inc; 2025 [Updated 2025 Apr 08; cited 2025 Jun 13]. Available from: https://www.uptodate.com/contents/atrioventricular-nodal-reentrant-tachycardia
  10. Biase LD, Walsh EP. Atrioventricular reentrant tachycardia (AVRT) associated with an accessory pathway. In Levy S, Knight BP, Botkin NF, editors. UptoDate [Internet]. UptoDate Inc; 2024 [Updated 2024 Nov 20; cited 2025 Jun 13]. Available from: https://www.uptodate.com/contents/atrioventricular-reentrant-tachycardia-avrt-associated-with-an-accessory-pathway
  11. Rodriguez Ziccardi M, Goyal A, Maani CV. Atrial Flutter. Treasure Island (FL): StatPearls Publishing; 2022.
  12. eTG complete [Internet]. Melbourne (AU): Therapeutic Guidelines LTd; 2017. Atrial fibrillation and atrial flutter [Updated 2024 Jul; cited 2025 Jun 13]. Available from:  https://app-tg-org-au.ap1.proxy.openathens.net/viewTopic?etgAccess=true&guidelinePage=Cardiovascular&topicfile=cardiovascular-disease-risk-stratification&guidelinename=auto&sectionId=c_CVG_Atrial-fibrillation-and-atrial-fluttertopic_8#c_CVG_Atrial-fibrillation-and-atrial-fluttertopic_8
  13. Heaton J, Yandrapalli S. Premature Atrial Contractions. Treasure Island (FL): StatPearls Publishing; 2023.
  14. Sattar Y, Hashmi MF. Premature Ventricular Complex. Treasure Island (FL): StatPearls Publishing; 2025. 
  15. Whitaker J, Wright MJ, Tedrow U. Diagnosis and management of ventricular tachycardia. Clin Med. 2023 Sep;23(5):442-448. Doi: 10.7861/clinmed.2023-23.5.
  16. Ludhwani D, Goyal A, Jagtap M. Ventricular Fibrillation. Treasure Island (FL): StatPearls Publishing; 2023.

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