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Abnormal Rhythms

Introduction

  • The focus of this section is on Arrhythmia (Abnormal Rhythm) which is synonymous with Dysrhythmia (bad rhythm).

Arrhythmia Overview

  • Definition:
      - Arrhythmia means 'without rhythm'.
      - Dysrhythmia refers to a 'bad rhythm', which is equivalent to arrhythmia.

Types of Arrhythmia

  • Common Types:
      - Premature Beats
      - Paroxysmal Tachycardia
      - Supraventricular Arrhythmias
      - Ventricular Arrhythmias

Rate of Tachy-Arrhythmia

  • Definitions of Tachycardia:
      - Tachycardia: 150-250 beats/min
      - Flutter: 250-350 beats/min
      - Fibrillation: > 350 beats/min

Premature Beats

  • Definition:
      - Premature beats are early beats that interrupt the underlying rhythm by occurring earlier than expected.

  • Types of Premature Beats:
      1. PACs (Premature Atrial Contractions)
      2. PJCs (Premature Junctional Contractions)
      3. PVCs (Premature Ventricular Contractions)

Premature Atrial Contractions (PACs)

  • Characteristics:
      - Early beats arising from areas in the atria other than the SA node, resulting in a different shape of the P Wave.
      - Conducted with a narrow QRS complex followed by a pause.

  • Etiologies:
      - Increased sympathetic input, exogenous stimulants, drug interactions, acute myocardial infarction (AMI), cardiac ischemia, idiopathic causes.

Premature Junctional Contractions (PJCs)

  • Characteristics:
      - Early beats stemming from the AV node or junction.
      - Often conducted with a narrow QRS complex.

  • Common Etiologies:
      - Ischemia, hypoxemia, valvular disease, digitalis toxicity, or normal variant conditions.

Premature Ventricular Contractions (PVCs)

  • Characteristics:
      - Early beats arising from the ventricles; display wide QRS complexes (>0.12 sec) that look different from normal sinus-conducted beats.
      - PVCs can occur as isolated events or may appear in patterns (pairs, triplets, repeating sequences).

  • Clinical Significance:
      - More than 6 PVCs/min suggests pathological conditions.
      - Three or more PVCs consecutively is termed a run of Ventricular Tachycardia (VT).
      - If VT persists for more than 30 seconds, it is classified as Sustained VT.

Comparison: PAC vs PVC

  • PACs:
      - Usually followed by an incomplete compensatory pause because the PAC resets the sinus node timing, leading to the next sinus P wave appearing earlier than expected.

  • PVCs:
      - Typically followed by a complete compensatory pause since the sinus node timing is not interrupted; the subsequent sinus impulse aligns with the sinus rate.

PVC Patterns

  • Couplets and Triplets:
      - PVCs can appear as couplets (two consecutive PVCs) or triplets (three consecutive PVCs).

  • Ventricular Bigeminy: PVCs occurring in patterns such that each normal complex is followed by a PVC.

Trigeminy and Quadrigeminy PVCs

  • Definitions:
      - Bigeminy: Occurrence of a PVC every other beat.
      - Trigeminy: Occurrence of a PVC every third beat.
      - Quadrigeminy: Occurrence of a PVC every fourth beat.

  • Clinical Implications:
      - Increased frequency of PVCs in patients with heart disease is predictive of ventricular fibrillation and sudden death.

  • Causes of PVCs:
      - Electrolyte imbalance, hypoxia, ischemia, acute myocardial infarction, and medication toxicity.

Runs of PVCs

  • Clinical Significance:
      - Presentation of runs indicates increased irritability within the ventricles, potentially leading to more severe arrhythmias.

Multifocal PVCs

  • Definition:
      - PVCs that show different shapes and sizes, indicating multiple ectopic foci in the ventricles.

R-on-T Phenomenon

  • Definition:
      - A phenomenon where a PVC occurs superimposing on the T wave of the previous beat's repolarization.
      - PVCs can occur early, after the T wave, or late in the cycle, occasionally resulting in a fusion beat.

  • Clinical Risk:
      - Particularly hazardous in acute ischemic conditions, as they heighten the risk of progression to ventricular tachycardia or fibrillation.

Summary of Various Forms of PVCs

  • Forms Covered:
      - Multifocal PVCs
      - Couplet
      - R-on-T phenomenon
      - Ventricular tachycardia
      - Ventricular bigeminy
      - Ventricular trigeminy

Paroxysmal Tachycardia

  • Definitions:
      - Paroxysmal Atrial Tachycardia
      - Paroxysmal Junctional Tachycardia
      - Paroxysmal Ventricular Tachycardia

Mechanisms of Arrhythmia

  • Four Mechanisms Identified:
      1. Reentry (most common)
      2. Automaticity
      3. Triggered Activity
      4. Parasystole

Detailed Mechanisms of Arrhythmias

  • Reentry Mechanism:
      - Illustrated by the analogy of a dog chasing its tail; involves abnormal conduction patterns or scar tissue that doesn’t conduct.
      - Episodes of arrhythmias due to reentrant circuits often start and end suddenly.

AV Node Re-Entrant Tachycardia

  • Pathway Details:
      - The fast pathway in the AV node conducts rapidly but has a longer recovery time.
      - The slow pathway conducts slowly but recovers quickly to initiate further beats.

  • Mechanism: PAC blocks in the fast pathway, conducts down the slow pathway, and then retrogrades back up the fast pathway.

Arrhythmias in Clinical Context

  • Common Arrhythmias:
      - Ventricular Tachycardia
      - Atrial Tachycardia
      - Atrial Fibrillation
      - Atrial Flutter
      - AV Reentry (such as in Wolff-Parkinson-White syndrome)

Paroxysmal Atrial Tachycardia (PAT)

  • Definition:
      - An event characterized by a sudden start and stop of tachycardia often occurring at 160-220 beats/min.
      - Result of reentrant activation fronts within the atria.

  • Causes:
      - Anxiety, stimulants (e.g., epinephrine), hypoxia, hyperthyroidism, menstrual onset in women.

Ectopic Atrial Tachycardia

  • Definition:
      - Identified by a dissimilar P wave compared to previous ECG traces, indicating an ectopic focus other than the SA node.

  • Paroxysmal Nature: Sudden and unpredictable outbursts of tachycardia.

Paroxysmal Junctional Tachycardia

  • Characteristics:
      - Fast and slow pathways within the AV junction create a reentrant rhythm exceeding 150 BPM, stimulating normal conduction pathways of the ventricles.
      - Regular R-R intervals, normal QRS complexes, and often inverted P waves buried within the QRS or following it.

Conclusion

  • Significance: Understanding of arrhythmias is essential for proper diagnosis and management, as well as recognizing their clinical implications in various contexts, including pre-existing heart conditions.