University:
West Coast University
Course:
PHAR 740 | IPC Cardiopulmonary and Renal III
Academic year:

2024
Views:

273

Pages:

53
Author:

Asal A.

Pathophysiology of Cardiac Arrhythmias Adam Kassan, PhD Associate Professor, Pharmaceutical Sciences West Coast University, School of Pharmacy Spring 2023 What is Cardiac Arrhythmia (Dysrhythmia)? Any deviation from normal heart rhythm • Disturbance in rate • Disturbance in site of origin • Disturbance in conduction of electrical impulse The Clinical Manifestation of Arrhythmias • • • • • • Palpitations Light-headedness Syncope Angina Congestive heart failure Sudden death Precipitating Factors (HIS DEBS) • Hypoxia  O2 deprivation, pulmonary disorders • Ischemia  MI, angina • Sympathetic Stimulation • Drugs • Electrolyte Disturbances:  hypo and hyperkalemia, imbalances in Ca2+ and Mg2+ • Bradycardia • Stretch  hypertrophy of atria and ventricles Clinical Classification of Arrhythmias • The ECG is invaluable for the diagnosis of arrhythmias • Cardiac arrhythmias can be divided into:  bradyarrhythmias: HR< 60bpm  tachyarrhythmias: HR>100bpm Bradyarrhythmias Tachyarrhythmias 350 250 150 100 60 40 20 Normal Rate Supraventricular Clinical Classification of Arrhythmias Sinus arrhythmias Atrial arrhythmias Junctional (nodal) arrhythmias Ventricular arrhythmias Arrhythmias Supraventricular SA node Bradyarrhythmias Tachyarrhythmias Ventricular Atria AV node Tachyarrhythmias Bradyarrhythmias • Sinus bradycardia • Sick sinus syndrome • Conduction (AV) block • Junctional escape rhythm Enhanced automaticity • Sinus tachycardia Triggered automaticity • Atrial premature beats Reentry mechanism • Multifocal atrial tachycardia • Atrial flutter • Atrial fibrillation Tachyarrhythmias Tachyarrhythmias Reentry mechanism • AV nodal reentrant tachycardia (AVNRT) • AV reciprocating tachycardia (AVRT) Triggered automaticity Reentry mechanism • Premature • Ventricular tachycardia ventricular • Ventricular fibrillation contractions (PVC) Arrhythmias Supraventricular SA node Bradyarrhythmias Tachyarrhythmias Ventricular Atria AV node Tachyarrhythmias Bradyarrhythmias • Sinus bradycardia • Sick sinus syndrome • Conduction (AV) block • Junctional escape rhythm Enhanced automaticity • Sinus tachycardia Triggered automaticity • Atrial premature beats Reentry mechanism • Multifocal atrial tachycardia • Atrial flutter • Atrial fibrillation Tachyarrhythmias Tachyarrhythmias Reentry mechanism • AV nodal reentrant tachycardia (AVNRT) • AV reciprocating tachycardia (AVRT) Triggered automaticity Reentry mechanism • Premature • Ventricular tachycardia ventricular • Ventricular fibrillation contractions (PVC) Sinus Bradycardia • Normal  rest, sleep, athletes • Pathologic  MI, hyperkalemia, hypothyroidism • Medications  β blockers, CCB Sinus Bradycardia • Parasympathetic  K+ channels opening o resting mb potential more negative  ↓ Ca2+ channel opening o affect phase 0 0 4 3 Sinus Bradycardia • ↓ ﬁring of the SA node • P wave and QRS complexes are normal  long RR (HR <60bpm) Arrhythmias Supraventricular SA node Bradyarrhythmias Tachyarrhythmias Ventricular Atria AV node Tachyarrhythmias Bradyarrhythmias • Sinus bradycardia • Sick sinus syndrome • Conduction (AV) block • Junctional escape rhythm Enhanced automaticity • Sinus tachycardia Triggered automaticity • Atrial premature beats Reentry mechanism • Multifocal atrial tachycardia • Atrial flutter • Atrial fibrillation Tachyarrhythmias Tachyarrhythmias Reentry mechanism • AV nodal reentrant tachycardia (AVNRT) • AV reciprocating tachycardia (AVRT) Triggered automaticity Reentry mechanism • Premature • Ventricular tachycardia ventricular • Ventricular fibrillation contractions (PVC) Sick Sinus Syndrome • Sinus arrest  SA node stops firing and nothing else happens o ECG flat line without electrical activity  SA node stops firing and AV node takes over o junctional escape • Sinoatrial block  failure of depolarization to be transmitted out of SA node • Bradycardia-tachycardia syndrome Arrhythmias Supraventricular SA node Bradyarrhythmias Tachyarrhythmias Ventricular Atria AV node Tachyarrhythmias Bradyarrhythmias • Sinus bradycardia • Sick sinus syndrome • Conduction (AV) block • Junctional escape rhythm Enhanced automaticity • Sinus tachycardia Triggered automaticity • Atrial premature beats Reentry mechanism • Multifocal atrial tachycardia • Atrial flutter • Atrial fibrillation Tachyarrhythmias Tachyarrhythmias Reentry mechanism • AV nodal reentrant tachycardia (AVNRT) • AV reciprocating tachycardia (AVRT) Triggered automaticity Reentry mechanism • Premature • Ventricular tachycardia ventricular • Ventricular fibrillation contractions (PVC) Sinus Tachycardia: Enhanced Automaticity • Enhanced  originate from pacemaker cells • Sympathetic  ↑opening of funny channels o phase 0 slope is higher o less time to reach threshold thus fast  ↑opening Ca2+ channels o phase 0 slope is higher 0 4 3 Sinus Tachycardia • SA node discharge >100/m (100 to 180 bpm) • Normal P waves and QRS complexes • Most often results from ↑ sympathetic Arrhythmias Supraventricular SA node Bradyarrhythmias Tachyarrhythmias Ventricular Atria AV node Tachyarrhythmias Bradyarrhythmias • Sinus bradycardia • Sick sinus syndrome • Conduction (AV) block • Junctional escape rhythm Enhanced automaticity • Sinus tachycardia Triggered automaticity • Atrial premature beats Reentry mechanism • Multifocal atrial tachycardia • Atrial flutter • Atrial fibrillation Tachyarrhythmias Tachyarrhythmias Reentry mechanism • AV nodal reentrant tachycardia (AVNRT) • AV reciprocating tachycardia (AVRT) Triggered automaticity Reentry mechanism • Premature • Ventricular tachycardia ventricular • Ventricular fibrillation contractions (PVC) Triggered Automaticity • Triggered  originate from the myocardial cells  act as foci to generate impulses Triggered Automaticity • Nonpacemaker cells may undergo depolarization  late phase 3: early afterdepolarization (EAD) o occur with prolonged action potential (congenital or drugs) o ion imbalance (hypokalemia)  early in phase 4: delayed afterdepolarization (DAD) o elevated intracellular Ca2+ EAD: Early After-Depolarization DAD: Delayed After-Depolarization Triggered Automaticity: Atrial premature beats • Atrial premature beats  abnormal P wave occurs earlier than expected • Abnormal impulse in atrial focus outside SA node • QRS is usually normal  ventricular conduction is usually not impaired Heart rate higher than normal (100-200 bpm) Triggered Automaticity: Atrial premature beats Common causes: • Digitalis toxicity • β-adrenergic stimulation • Caffeine • Alcohol • Stimulant drugs  cocaine, amphetamines Arrhythmias Supraventricular SA node Bradyarrhythmias Tachyarrhythmias Ventricular Atria AV node Tachyarrhythmias Bradyarrhythmias • Sinus bradycardia • Sick sinus syndrome • Conduction (AV) block • Junctional escape rhythm Enhanced automaticity • Sinus tachycardia Triggered automaticity • Atrial premature beats Reentry mechanism • Multifocal atrial tachycardia • Atrial flutter • Atrial fibrillation Tachyarrhythmias Tachyarrhythmias Reentry mechanism • AV nodal reentrant tachycardia (AVNRT) • AV reciprocating tachycardia (AVRT) Triggered automaticity Reentry mechanism • Premature • Ventricular tachycardia ventricular • Ventricular fibrillation contractions (PVC) Reentry Mechanism • A disorder of impulse transmission • Abnormal conduction pathway  slow rate of wave propagation  unidirectional block • Caused by temporary depolarization block or premature action potential • Wave of excitation form a reentrant loop Arrhythmias Supraventricular SA node Bradyarrhythmias Tachyarrhythmias Ventricular Atria AV node Tachyarrhythmias Bradyarrhythmias • Sinus bradycardia • Sick sinus syndrome • Conduction (AV) block • Junctional escape rhythm Enhanced automaticity • Sinus tachycardia Triggered automaticity • Atrial premature beats Reentry mechanism • Multifocal atrial tachycardia • Atrial flutter • Atrial fibrillation Tachyarrhythmias Tachyarrhythmias Reentry mechanism • AV nodal reentrant tachycardia (AVNRT) • AV reciprocating tachycardia (AVRT) Triggered automaticity Reentry mechanism • Premature • Ventricular tachycardia ventricular • Ventricular fibrillation contractions (PVC) Multifocal Atrial tachycardia (MAT) • Results from random firing of several ectopic atrial foci  combination of both re-entry and triggered activity • Irregular rhythm with a rate of 100-200 bpm • At least 3 distinctive P-wave morphologies Arrhythmias Supraventricular SA node Bradyarrhythmias Tachyarrhythmias Ventricular Atria AV node Tachyarrhythmias Bradyarrhythmias • Sinus bradycardia • Sick sinus syndrome • Conduction (AV) block • Junctional escape rhythm Enhanced automaticity • Sinus tachycardia Triggered automaticity • Atrial premature beats Reentry mechanism • Multifocal atrial tachycardia • Atrial flutter • Atrial fibrillation Tachyarrhythmias Tachyarrhythmias Reentry mechanism • AV nodal reentrant tachycardia (AVNRT) • AV reciprocating tachycardia (AVRT) Triggered automaticity Reentry mechanism • Premature • Ventricular tachycardia ventricular • Ventricular fibrillation contractions (PVC) Atrial Flutter • Generated by a reentry circuit that runs largely in the RA  leads to large parts of the atrium to be depolarized  typical ”sawtooth” appearance (F wave) • Regular atrial activation with a rate of 250-350 bpm • Many of these pulses reaches the AV nodes during its refractory period  do not conduct to the ventricles  resulting in a slower ventricular rate Arrhythmias Supraventricular SA node Bradyarrhythmias Tachyarrhythmias Ventricular Atria AV node Tachyarrhythmias Bradyarrhythmias • Sinus bradycardia • Sick sinus syndrome • Conduction (AV) block • Junctional escape rhythm Enhanced automaticity • Sinus tachycardia Triggered automaticity • Atrial premature beats Reentry mechanism • Multifocal atrial tachycardia • Atrial flutter • Atrial fibrillation Tachyarrhythmias Tachyarrhythmias Reentry mechanism • AV nodal reentrant tachycardia (AVNRT) • AV reciprocating tachycardia (AVRT) Triggered automaticity Reentry mechanism • Premature • Ventricular tachycardia ventricular • Ventricular fibrillation contractions (PVC) Atrial Fibrillation • Uncoordinated, repetitive excitation of myocytes  writhing movement of the chamber wall, with no effective blood ejection • Sustained by multiple local abnormal circuits • Excitation is transmitted sporadically through the AV node to the ventricles • Small, irregular ‘f’ waves replace the P waves • Risk of embolism no P waves + irregular R-R intervals. >350-500 discharge/min Arrhythmias Supraventricular SA node Bradyarrhythmias Tachyarrhythmias Ventricular Atria AV node Tachyarrhythmias Bradyarrhythmias • Sinus bradycardia • Sick sinus syndrome • Conduction (AV) block • Junctional escape rhythm Enhanced automaticity • Sinus tachycardia Triggered automaticity • Atrial premature beats Reentry mechanism • Multifocal atrial tachycardia • Atrial flutter • Atrial fibrillation Tachyarrhythmias Tachyarrhythmias Reentry mechanism • AV nodal reentrant tachycardia (AVNRT) • AV reciprocating tachycardia (AVRT) Triggered automaticity Reentry mechanism • Premature • Ventricular tachycardia ventricular • Ventricular fibrillation contractions (PVC) Defects of Conduction or Heart Block • Heart block  defect in the conduction system of the heart  SA node block  AV block  Bundle branch block Defects of Conduction or Heart Block AV block • Three degrees:  first degree  second degree o Mobitz type I o Mobitz type II  3rd degree Defects of Conduction or Heart Block First Degree AV Block • Conduction passes from SA node to ventricles  but abnormally delayed at the AV node o PR interval >0.2s Defects of Conduction or Heart Block Second Degree AV block • Not every atrial impulse is able to pass through the AV node into the ventricles • 2 types of second-degree AV block  Mobitz type I second-degree AV block o more commonly called Wenckebach block  Mobitz type II second-degree AV block Defects of Conduction or Heart Block Second Degree AV block Mobitz type I (Wenckebach phenomenon) • Almost always a block within the AV node • PR interval lengthens with each beat, until transmission fails completely • Transient and benign  rarely progresses to 3rd degree heart block P P P P P Defects of Conduction or Heart Block Second Degree AV block Mobitz type II • Usually due to a block below the AV node in the His bundle • Sudden loss of AV conduction  without preceding gradual lengthening of the PR interval • Serious and can suddenly progress to 3rd degree heart block Defects of Conduction or Heart Block Third Degree AV Block • Transmission from SA nodes to ventricles fails completely  often called complete heart block • Atria and ventricles beat independently, at different rates • Can be caused by degenerative diseases of the conduction system • Patients are treated by artificial pacemaker implantation Arrhythmias Supraventricular SA node Bradyarrhythmias Tachyarrhythmias Ventricular Atria AV node Tachyarrhythmias Bradyarrhythmias • Sinus bradycardia • Sick sinus syndrome Tachyarrhythmias Tachyarrhythmias • Conduction (AV) block • Junctional escape rhythm Enhanced automaticity • Sinus tachycardia Triggered automaticity • Atrial premature beats Reentry mechanism • Multifocal atrial tachycardia • Atrial flutter • Atrial fibrillation Reentry mechanism • AV nodal reentrant tachycardia (AVNRT) • AV reciprocating tachycardia (AVRT) Triggered automaticity Reentry mechanism • Premature • Ventricular tachycardia ventricular • Ventricular fibrillation contractions (PVC) Junctional Escape Rhythm SA node impaired: • AV nodes fires  junctional escape rhythm o no P but QRS are normal Arrhythmias Supraventricular SA node Bradyarrhythmias Tachyarrhythmias Ventricular Atria AV node Tachyarrhythmias Bradyarrhythmias • Sinus bradycardia • Sick sinus syndrome • Conduction (AV) block • Junctional escape rhythm Enhanced automaticity • Sinus tachycardia Triggered automaticity • Atrial premature beats Reentry mechanism • Multifocal atrial tachycardia • Atrial flutter • Atrial fibrillation Tachyarrhythmias Tachyarrhythmias Reentry mechanism • AV nodal reentrant tachycardia (AVNRT) • AV reciprocating tachycardia (AVRT) Triggered automaticity Reentry mechanism • Premature • Ventricular tachycardia ventricular • Ventricular fibrillation contractions (PVC) AV Nodal Reentrant Tachycardia AVNRT • Reentrant circuit looping within the AV node • Sudden onset  usually initiated by a premature supraventricular beat • Termination is just as abrupt. It can occur in perfectly normal hearts • Regular rhythm  usually between 150 and 250 b/min Arrhythmias Supraventricular SA node Bradyarrhythmias Tachyarrhythmias Ventricular Atria AV node Tachyarrhythmias Bradyarrhythmias • Sinus bradycardia • Sick sinus syndrome • Conduction (AV) block • Junctional escape rhythm Enhanced automaticity • Sinus tachycardia Triggered automaticity • Atrial premature beats Reentry mechanism • Multifocal atrial tachycardia • Atrial flutter • Atrial fibrillation Tachyarrhythmias Tachyarrhythmias Reentry mechanism • AV nodal reentrant tachycardia (AVNRT) • AV reciprocating tachycardia (AVRT) Triggered automaticity Reentry mechanism • Premature • Ventricular tachycardia ventricular • Ventricular fibrillation contractions (PVC) Accessory Pathway • A discrete aberrant conducting pathway  connects the atria and ventricles • Acts as a short circuit  allowing the atrial wave of depolarization to bypass AV node and activate the ventricles prematurely Wolff-Parkinson-White Syndrome (WPW) • A tachyarrhythmia most often seen in WPW is the supraventricular tachycardia (>200bpm) • Reentry from the accessory bundle of Kent  faster ventricular stimulation (preexcitation)  short PR interval • Wide QRS: delta wave (combination of 2 signals):  bundle of Kent stimulates ventricles  AV will excite the Purkinje, then ventricles Wolff-Parkinson-White Syndrome (WPW) AV reciprocating Tachycardia (AVRT) • In WPW the reentrant loop reciprocates between the atria and ventricles  the arrhythmia is more accurately termed AV reciprocating tachycardia (AVRT) Orthodromic AVRT Antidromic AVRT Arrhythmias Supraventricular SA node Bradyarrhythmias Tachyarrhythmias Ventricular Atria AV node Tachyarrhythmias Bradyarrhythmias • Sinus bradycardia • Sick sinus syndrome • Conduction (AV) block • Junctional escape rhythm Enhanced automaticity • Sinus tachycardia Triggered automaticity • Atrial premature beats Reentry mechanism • Multifocal atrial tachycardia • Atrial flutter • Atrial fibrillation Tachyarrhythmias Tachyarrhythmias Reentry mechanism • AV nodal reentrant tachycardia (AVNRT) • AV reciprocating tachycardia (AVRT) Triggered automaticity • Premature ventricular contractions (PVC) Reentry mechanism • Ventricular tachycardia • Ventricular fibrillation Triggered automaticity Premature Ventricular Contractions (PVCs) • Most common of the ventricular arrhythmias • Triggered  sympathetic, alcohol, β adrenergic receptor inducers (inhalers, cocaine) • QRS complex is wide and bizarre • P wave is usually absent • Usually followed by a prolonged compensatory pause • Typically occur randomly (A)  may alternate in regular pattern (B) A PVC. Note the compensatory pause before the next beat Bigeminy. PVCs and sinus beats alternate in a 1:1 fashion Arrhythmias Supraventricular SA node Bradyarrhythmias Tachyarrhythmias Ventricular Atria AV node Tachyarrhythmias Bradyarrhythmias • Sinus bradycardia • Sick sinus syndrome • Conduction (AV) block • Junctional escape rhythm Enhanced automaticity • Sinus tachycardia Triggered automaticity • Atrial premature beats Reentry mechanism • Multifocal atrial tachycardia • Atrial flutter • Atrial fibrillation Tachyarrhythmias Tachyarrhythmias Reentry mechanism • AV nodal reentrant tachycardia (AVNRT) • AV reciprocating tachycardia (AVRT) Triggered automaticity Reentry mechanism • Premature • Ventricular tachycardia ventricular • Ventricular fibrillation contractions (PVC) Ventricular Tachycardia (VT) • A run of three or more consecutive PVCs • Rate of 120 to 200 bpm  may be slightly irregular • An emergency, indicating cardiac arrest • ~3.5% of patients develop VT after MI within the first 48h • Development of sustained VT within the first 6 weeks post-infarction  associated with a high 1-year mortality rate Ventricular Tachycardia (VT) Morphology of waveform may be: • Uniform  healed infarctions • Polymorphic  acute coronary ischemia, infarction, QT interval prolongation Ventricular Tachycardia (VT) Torsades de Pointes • Torsades de pointes, meaning “twisting of the points • Unique form of ventricular tachycardia  seen in patients with prolonged QT intervals  caused by o congenital genetic mutations o electrolyte disturbances o acute myocardial infarction o medications Ventricular Tachycardia (VT) Torsades de Pointes • A prolonged QT interval is the result of prolonged ventricular repolarization  a PVC falling during the elongated T wave can initiate torsade de pointes • QRS complexes spiral around baseline • Risk of degeneration into ventricular fibrillation Ventricular Fibrillation (VF) • Seen almost solely in dying hearts • The most frequently encountered arrhythmia in adults who experience sudden death • There are no true QRS complexes  multiple small waves abnormal impulses in the ventricle  rippling motion of the ventricle wall (fibrillation) o cessation of CO • Cardioversion (defibrillation)

Pathophysiology of Cardiac Arrhythmias

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