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Cardiac arrhythmias-an overview

A cardiac arrhythmia simply defined is a variation from the normal heart rate and or rhythm that is not physiologically justified ( Antzelevitch et al Overview of Basic Mechanism of Cardia Arrhythmia 2011 )

 

only normal rhythm of the heart is the sinus rhythm ( SR ) SA node is a cluster of cells at the junction of superior vena cava and high right lateral atrium impulse generated from the Sinus node ( SA ) is conducted through and slowed down while passing through the atrioventricular node
( AV ) -its conducted through bundle of His , to the left and right branches and eventually into the Purkinje fibers AV node is located on the right side of the interatrial septum atrial contraction is always followed by ventricular contraction term dysrhythmia is also used to describe arrhythmia & has similar meaning.

 

prevalence of arrhythmias is expected to be 1.5 % to 5 % in the general population atrial fibrillation is the most common sustained cardiac arrhythmia globally about 90,000 cases of supraventricular tachycardia are detected annually in the US

 

arrhythmias happen due to alterations of impulse formation or alterations of impulse conduction once arrhythmias are initiated they can be maintained by three common etiologies – accelerated automacity , reentry ( or circus movement ) and triggered activity most bradyarrhythmias happen due to decreased intrinsic pacemaker function or blocks in conduction within the AV node or the His-Purkinje system most tachyarrhythmias are caused by reentry while some result from enhanced automacity or from abnormal mechanisms of automacity hypertensive heart disease can manifest as many cardiac arrhythmias – most common being AF patients with LVH due to hypertension are at risk of both supraventricular and ventricular arrhythmias patients are at increased risk in the days following cardiac surgery.

 

associated with substantial morbidity & societal economic costs significant public health problem & associated with decreased QoL & increased risk of morbidity & mortality ( ESC ) ventricular arrhythmias are thought to cause 75 % to 80 % of sudden cardiac deaths ( in the US ) it is also estimated that serious ventricular tachyarrhythmias are the cause of death in nearly 50 % of patients with coronary artery disease (India ) ventricular arrhythmia events are closely associated with SCD in patients with IHD- hence ECS guidelines recommends prophylactic implantable cardioverter-defibrillator ( ICD ) in MI patients with reduced LVEF.

 

good clinical history physical examination age , gender known risk factors for arrhythmias ( e,g hypertension , CAD , heart failure , diabetes , cardiomyopathy ) full list of medications family history ( e.g h/o SCD ) risk of AF is significantly higher with increasing age and lifetime risk is generally higher in men people with conditions as hypertension , obesity , sleep apnoea ar at higher risk of AF and opportunistic screening for AF should be considered people with heart failure should be screened for AF.

 

may have no signs & symptoms palpitation or fluttering sensation in chest racing heart feeling of a skipped beat can be paroxysmal fatigue , inability to concentrate , cognitive impairment , dizziness , SOB or exercise intolerance vertigo , blurred vision , light headedness , syncope symptoms will also depend on the duration of arrhythmia , if it is consistent or intermittent , severity and if it affects the cardiac output.

 

rate ( tachycardia or bradycardia ) rhythm ( regular or irregular ) origin of impulse ( supraventricular , ventricular or artificial pacemaker ) impulse conduction ( ie atrioventricular , ventriculo-atrial or block ) ventricular rate.

 

standard 12 lead ECG – first line exercise ECG in patients with arrhythmia related to exertion ambulatory ECG loop event recorders implantable loop recorders imaging modalities for risk assessment of sudden cardiac death ( SCD ) as
○ evaluation of LV ejection fraction
○ echocardiography – structural heart disease
○ cardiac MRI or CT electrophysiology smartphones , wearables & related technologies

 

Supraventricular tachycardia -originates from above the AV node
 atrial fibrillation atrial flutter atrial tachycardia atrial premature complex atrioventricular nodular reentrant tachycardia ( AVNRT ) atrioventricular reentrant tachycardia ( AVRT ) AV junctional extrasystoles.

 

Ventricular tachycardia -origin below the AV node
 ventricular fibrillation ( V-fib) ventricular premature beats 
( PVC ) ventricular tachycardia 
( sustained or non-sustained ) Torsades De Pointes

 

Narrrow complex tachycardia -QRS < 120 ms
 sinus tachycardia atrial tachycardia atrial flutter AVNRT AVRT junctional ectopic tachycardia sinoatrial nodal reentrant tachycardia atrial fibrillation.

 

monomorphic ventricular tachycardia poymorphic VT or V-Fib

 

Bradyarrhythmias -can be physiological ( as in athletes ) dysfunction in the conduction system which can be at 
○ level of sinus node
○ atrioventricular node or
○ His – Purkinje system the most common primary cause of bradyarrhythmias is aging leading to fibrosis and degeneration of the conduction system & the pacemaker cells risk factors for bradyarrhythmias include hypertension , diabetes and chronic IHD.

 

Sinus node dysfunction
( Sick sinus
 syndrome ) sinus bradycardia sinus arrest SA blocks brady-tachy forms chronotrophic incompetence.

 

Atrioventricular blocks 1st degree 2nd degree ( Mobitz I & II ) 3rd degree or complete AV block.

 

Intraventricular conduction abnormalities bundle branch blocks fascicular hemiblocks bifascicular block trifascicular block.

 

Drugs causing bradyarrhythmia rate limiting calcium channel blockers antiarrythmic drugs as amiodarone , sotalol , flecainide digoxin ivabradine beta blockers 5 HT3 receptor antagonists-antiemetics.

References

  1. Desai DS, Hajouli S. Arrhythmias. [Updated 2021 Jun 18]. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2021 Jan-. Available from: https://www.ncbi.nlm.nih.gov/books/NBK558923/
  2. Alireza Sepehri Shamloo, T Jared Bunch, Yenn-Jiang Lin, Marcio Jansen de Oliveira Figueiredo, Nikolaos Dagres, Jens Cosedis Nielsen, Risk Assessment in Cardiac Arrhythmias, European Heart Journal, Volume 41, Issue 47, 14 December 2020, Pages 4455–4457, https://doi.org/10.1093/eurheartj/ehaa808
  3. Bradyarrhythmias bradyarrhythmias.pdf (cuni.cz)
  4. Naik, Nitish, et al. “Epidemiology of Arrhythmias in India: How Do We Obtain Reliable Data?” Current Science, vol. 97, no. 3, Current Science Association, 2009, pp. 411–15, http://www.jstor.org/stable/24112009. ( Abstract )
  5. Antoni H. Pathophysiologie der Herzrhythmusstörungen [Pathophysiology of cardiac arrhythmias]. Z Kardiol. 1992;81 Suppl 4:111-7. German. PMID: 1290287. ( Abstract )
  6. Karpawich P.P. (2015) Pathophysiology of Cardiac Arrhythmias: Arrhythmogenesis and Types of Arrhythmias. In: Jagadeesh G., Balakumar P., Maung-U K. (eds) Pathophysiology and Pharmacotherapy of Cardiovascular Disease. Adis, Cham. https://doi.org/10.1007/978-3-319-15961-4_47 ( Abstract )

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