Arrhythmias

Sinus Arrhythmia

Sinus Rhythm:

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

Supraventricular Tachycardia (SVT)

Definition:

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:

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