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


  • 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


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


Definition: Three successive beats faster than normal for age.


  • 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


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)


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


  • 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


  • Irregularly irregular rate

  • Intermittent P waves

  • If WPW, may have variable QRS morphology

Ventricular Tachycardia


Wide QRS tachycardia originating in the ventricle


  • 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:


  • Connect catheter and grounding pad to generator

  • Apply current at radiofrequency

  • Observe effects


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


It is used in the treatment of

  • SVT

  • Flutter

  • VT


  • Applications are the same

  • Procedure maybe excision or cryosurgery

Arrhythmias Arrhythmias 2001-01-18
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