Arrhythmias
N C Joshi
Consultant Pediatrician, Nanavati Hospital, Mumbai, India
First Created: 01/18/2001 

Sinus Arrhythmia

Sinus Rhythm:

Rhythm originating in the sinus node

Sinus Arrhythmia

Definition: Irregular rhythm originating in the sinus node.

(P-P interval varies >0.08 sec)

Arrhythmia With Normal Heart Rate

They are seen in the following conditions:

Arrhythmia with narrow QRS,

  • Wandering atrial pacemaker

  • Aberrant atrial pacemaker

  • Accelerated junctional rhythm

Arrhythmia with wide QRS

  • Accelerated ventricular rhythm

  • Sinus with aberrancy

  • Accelerated junctional rhythm with aberrancy

QRS Complex

Consider the following when looking at the QRS complex

  • Regular or irregular

  • How fast?

  • P-waves: Narrow or wide

  • P-wave axis

  • Association of P-waves to QRS

Narrow QRS : Infant <80 msec, Child <85 msec. It is generally supraventricular in origin. Generally requires activation through bundle of His

Wide QRS: It is often of ventricular origin. Also seen with Aberrant conduction (Rate-related versus present in sinus). There may be the presence of an accessory connection. Associated with drug effects. Seen with electrolyte imbalance.

Wide QRS of Ventricular origin : The following is supportive of ventricular origin:

  • Positive concordance (If no RVH)

  • AV dissociation

Wide QRS of Aberrancy

Fixed bundle branch block

  • Common in post-op hearts

  • Reflects conduction system disease in unoperated hearts

    Rate-related

  • Ashman phenomenon

  • Failure of bundle to consistently conduct at higher rates

  • Usually refractory period of right bundle is more than left bundle

Wide QRS of Accessory connection

  • Bundle Branch morphology: opposite location of accessory connection

  • May be present intermittently in sinus rhythm

Wide QRS of Drug effects

  • Type IA anti-arrythmics

  • Tricyclic antidepressants

Wide QRS of Electrolytes

  • Hyperkalemia

  • Hypoxia and acidosis

Bradycardia

It is calculated from the lowest heart rate for 6 sec in normal individuals. It is defined as less than

  • 68 BPM in Infants

  • 42 BPM in Child

  • 26 BPM in Adolescent

Causes of bradycardia:

  • Sinus bradycardia

  • Atrial escape

  • Junctional escape

  • Ventricular escape

  • Asystole

Causes of Bradycardia with narrow QRS:

  • Sinus arrhythmia or bradycardia

  • Wandering atrial pacemaker (Atrial escape)

  • Junctional escape (40-60 BPM)

Causes of Bradycardia with wide QRS:

  • Ventricular Escape (30-40 BPM)

  • Escape above bifurcation of His with aberrancy

Tachycardia

Definition: Three successive beats faster than normal for age.

Types:

  • Sinus tachycardia

  • Atrial tachycardia

  • Junctional tachycardia

  • Ventricular tachycardia

Tachycardia with Narrow QRS:

  • SVT

  • Flutter

  • Atrial Fibrillation

  • Junctional tachycardia

Tachycardia with wide QRS:

  • Ventricular tachycardia

  • SVT with aberrancy

  • Junctional tachycardia with aberrancy

  • Ventricular Fibrillation

Mechanism of formation of tachycardia:

Disorders of impulse formation

  • Abnormal automaticity

  • Triggered dysrhythmia

    Disorders of impulse propagation

  • Re-entry

  • Reflection

Abnormal Automaticity

Re-entry

Anatomical Malformations causing reentry:

  • Bypass tracts

  • Dual AV Nodal Pathways

  • Damaged tissue

  • Anatomical obstruction

  • Anisotropy

Figure 1: Mechanism for re-entry


Mechanism for Reentry

Supraventricular Tachycardia (SVT)

Definition:

Tachycardia resulting from an abnormal mechanism dependent upon structures above the bifurcation of the bundle of His for propagation and excluding atrial flutter or fibrillation.

Characteristics in Children

  • 90% narrow QRS

  • May be difficult to see P wave

  • Orientation and location of P waves suggest mechanism of tachycardia

  • BPM usually around 300

Mechanisms of Supraventricular Tachycardia:

Probable Re-entrant Mechanism

  • Orthodromic reciprocating

  • Antidromic reciprocating

  • AV nodes re-entry

  • Permanent junctional reciprocating tachycardia (PJRT)

  • Sinus node reentry

  • Atrial muscle re-entry

Presence of Bypass Tracts

  • Atrioventricular or accessory connections

  • Wolff-Parkinson-White

  • Unidirectional retrograde accessory pathway (URAP)

  • intranodal pathways

  • Dual AV nodal pathways

Probable Abnormal Automaticity

  • Atrial ectopic tachycardia(AET)

  • Chaotic atrial tachycardia s

  • Junctional ectopic tachycardia

Atrial Flutter

Characteristics:

  • Typical saw-toothed P waves

  • Rate 280-450 BPM (Infants may have even 500BPM!)

  • Atypical in Post-op hearts

  • May be modified by drugs

Atrial Fibrillation

Characteristics:

  • Irregularly irregular rate

  • Intermittent P waves

  • If WPW, may have variable QRS morphology

Ventricular Tachycardia

Definition:

Wide QRS tachycardia originating in the ventricle

Characteristics:

  • Dissociation from atria proves Ventricular tachycardia

  • Change in morphology of QRS (particularly if abnormal in sinus)

Electrophysiological (EP) Study

Why is it required?

  • To determine if tachycardia is present

  • To determine the mechanism of tachycardia

  • For drug testing if tachycardia is present

  • To locate the origin of critical structures

  • Ablation of the origin of critical structures

Arrhythmias - Treatment

Depends on mechanism

  • For abnormal automaticity: Decrease Phase 4 depolarization

  • For Re-entry: Reduce the excitable gap

  • For Both: eliminate the source (radiofrequency ablation or surgery)

Radiofrequency Ablation:

Procedure:

  • Connect catheter and grounding pad to generator

  • Apply current at radiofrequency

  • Observe effects

Mechanism:

It causes a thermal burn. Tip temperature is approximately 70 degree Celsius

Applications:

It is used in the treatment of

  • SVT

  • Flutter

  • VT

Surgery:

  • Applications are the same

  • Procedure maybe excision or cryosurgery


Arrhythmias Arrhythmias 01/18/2001
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