ARRHYTHMIA

Spectrum of cardiac arrhythmia in childhood spans from common benign rhythm irregularities, e.g. premature or ectopic beats, to rare life-threatening arrhythmia, e.g. ventricular fibrillation.

Clinical indicators: Cardiac arrhythmias are not uncommon in children, though many cases remain unrecognized. Presence of arrhythmia should always be suspected in a case with-(a) irregular heart beats,

(b) disproportionate tachycardia/bradycardia, (c) unexplained/non-responsive CCF, (d) recurrent attacks of syncope, palpitation or chest pain, (e) family history of sudden deaths, and (f) past history of arrhythmia.

Etiology: Arrhythmia may be congenital with/without structural CHDs or acquired following—(a) rheumatic fever/heart disease, (b) myocarditis or myocardiopathies,

(c) drugs, e.g. theophylline, digoxin, and (d) cardiac surgery.

TABLE 17.33: Cardiac arrhythmias in childhood

• Benign and common abnormalities

- Sinus arrhythmia

- Sinus bradycardia

- Extra-systoles

- Premature atrial/ventricular complexes

• Tachy-arrhythmias

- Supraventricular tachycardia

- Atrial AutterZfibrillation

- Ventricular tachycardia

- Ventricular flutter/fibrillation

- Long Q-T syndrome

• Brady-arrhythmias

- Sinus arrest/sinoatrial block

- AVblocks: 1 ^st, 2^nd and 3^rd degree

- Congenital complete AV block

• Sick sinus syndrome

- Bradycardia-Tachycardia syndrome

Classification: Arrhythmia may be broadly classified as: (a) benign rhythm irregularities, (b) tachyarrhythmias, (c) bradyarrhythmias, and (d) sick-sinus syndrome, i.e. alternating tachy#8730;brady-arrhythmias (Table 17.33).

Salient features of important arrhythmias are dis­cussed here with characteristic ECG changes in Fig.

Sinus arrhythmia is accentuation of normal physio­logical variation with a slowing of heart rate (HR) during expiration and acceleration during inspiration. Sinus arrhythmia is common in preterms, febrile patients or drugs, e.g. digoxin therapy. It is usually abolished by exercise.

Sinus bradycardia denotes HR lt;90 in newborns or lt;60 in older children. It is common in athletes and myxedema and needs to be differentiated from SA block or AV block. Children with sinus bradycardia are able to increase their HR gt;100 with exercise, unlike those with SA/AV blocks. Extrasystoles indicate discharge from an ectopic focus in atrial, junctional or ventricular tissues, i.e. other than SA node. Isolated extrasystoles are of no significance, unless associated with underlying heart disease or digoxin therapy.

Premature atrial complexes (PAC), characterized by presence of P waves with normal, prolonged or absent QRS complexes and without compensatory pause are common, even in normal children.

Premature ventricular complexes (PVC) are characte­rized by premature, wide and bizarre QRS complexes, often associated with compensatory pause. When frequent, PVCs may assume a definite rhythm, i.e. bigeminy (alternating with normal beats) or trigeminy (after two normal beats). Although benign PVCs are common in anxiety, febrile illnesses and stimulant drug therapy, presence of two or more consecutive PVCs or increased frequency after exercise indicates potential risk of

Fig. 17.24: ECG changes in common arrhythmia.

degeneration into more severe arrhythmia. IV Lidocaine is drug of choice in these cases.

Supraventricular tachycardia (SVT) or paroxysmal atrial tachycardia (PAT) is characterized by abrupt onset and cessation of severe tachycardia (gt;180-220#8725;min), originating proximal to the bifurcation of the bundle of His due to an abnormal mechanism (specifically excluding sinus tachycardia).

Etiologically, SVT is usually associated with—(a) acute infection, (b) use of sympathomimetic drugs, e.g. decongestants, or (c) underlying heart disease in 20% cases, e.g. Ebstein anomaly.

Pathophysiologically, SVT may be caused by—(a) re-entry of a premature atrial wave back into atrium due to refractory AV node (echo beats) using an accessory pathway (commonest type in 90% cases), (b) re-entry without accessory pathway and (c) ectopic or automated tachycardia.

Re-entry SVT are further classified as atrioventricular reentry tachycardia (AVRT) or atrioventricular nodal reentry tachycardias (AVNRT).

Clinically, while short episodes are well tolerated except palpitation, prolonged attacks may lead to CCF. Infants may present with feeding problems, irritability and shock.

ECG changes are often limited to tachycardia and narrow QRS complexes during the attack, but may show typical features of Wolff-Parkinson-White syndrome, i.e. short PR interval with slow upstroke of QRS complex (delta wave). A 12-lead ECG is essential before starting the treatment, while 24-hour ECG (Holter monitoring) is necessary to detect brief and asymptomatic attacks.

Treatment of SVT includes:

• Abolition of acute attack by

± Vagal stimulation by immersion in ice-cold water, Valsalva maneuver, breath-holding, etc.

- Drugs, e.g. IV adenosine* (drug of choice; 50-300 mg/kg bolus) followed by propranolol, etc., to prevent the recurrence.

- Synchronized DC cardioversion

• Maintenance therapy with digoxin, propranolol or verapamil.

• Radio-frequency ablation of accessory pathway.

*Adenosine has a very short half-life of lt;10 seconds and should be given as a rapid bolus through a large vein near the heart, (e.g. antecubital fossa) flushed immediately with 5 ml normal saline. Begin with the first bolus of 100 #956;g#8725;kg and repeat every 2 minutes in incremental doses till response or maximum dose of 500 #956;g#8725;kg (300 #956;g#8725;kg in newborns) is reached.

Prognosis for complete resolution of SVT depends on age of onset and etiology. SVT diagnosed in infancy is likely to resolve in 70-80% as compared to only in 33% patients diagnosed after 1 year of age.

Atrial flutter presents with regular or regularly irregular tachycardia (HR: 250-400/min), due to a micro-reentrant loop in atrial tissue and some form of anatomical obstruction/discontinuity in conduction passage, e.g. fibrosis, valve annulus, etc.

It is most commonly seen in cardiac cases with dilated atria, e.g. rheumatic MS, tricuspid atresia or Ebstein anomaly. Diagnosis is confirmed on ECG with rapid and regular saw-toothed flutter waves. DC cardioversion is the treatment of choice in emergency, followed by digoxin therapy, with/without quinidine or procainamide for long-term control.

Atrial fibrillation is rare in children, presenting with very rapid and chaotic atrial excitation, i.e. fibrilla- tory waves (300-700 #8725;min) and irregularly irregular ventricular response. It may develop in conditions producing atrial flutter or after cardiac surgery. Digi­talization, followed by DC cardioversion or quinidine therapy is the treatment of choice.

Note: All IV anti-arrhythmic agents should be infused slowly except adenosine (see below) with constant BP and ECG monitoring.

¹If no response to vagotonic maneuvers. Use DC cardioversion in critically-sick patients. ² Cardioversion is preferred choice. ³ Defibrillation is preferred choice. ⁴ Extremely short-acting, start with 50 mg/kg/dose and repeat every 2 min with increasing doses by 50-100 mg/kg till response. SVT: Supraventricular tachycardia; VPC: Ventricular premature contractions; PVC: Premature ventricular complexes; AFl: Atrial flutter; AFb: Atrial fibrillation; VT: Ventricular tachycardia; VF: Ventricular fibrillation; LQTS: Long QT syndrome; JET: Junctional ectopic tachycardia

Ventricular tachycardia, defined as at least 3 PVCs at HR gt;120#8725;min, is less common than SVT in children.

Long QT syndrome (LQTS) is a rare cause of recurrent syncopal attacks and sometimes sudden death due to a malignant ventricular arrhythmia—torsades de pointes. Nearly 50% cases are familial, with abnormalities in cardiac Na⁺#8725;K⁺ channels. Diagnosis is based on:

• history of unexplained and recurrent syncopal attacks,

• typical ECG findings with QTc interval gt;0.47 and

• family history of sudden death or LQTS.

Treatment includes #946;-blockers to blunt the HR response to exercise and use of pacemakers.

Atrioventricular (AV) blocks, the commonest brady­arrhythmia, may be divided into:

• 1^st degree heart, block, i.e. prolonged PR interval but all atrial impulses are conducted to ventricle.

• 2^nd degree heart, block, where some atrial impulses are not conducted to ventricle. It includes:

± Wenckebach type or Mobitz type I, with constant PP interval but PR interval increasing progressively till a dropped beat. The ensuing PR interval is again normal and cycle is repeated.

± Mobitz type II, where occasional atrial beat is not conducted to ventricle.

3^rd degree or complete heart block, where no atrial impulse is conducted to ventricle.

Complete heart block may be congenital or acquired. Congenital complete heart block is common in babies born to mothers with SLE or other connective tissue disorders. Acquired heart blocks may develop in—(a) complex CHDs, (b) myocarditis, (c) after cardiac surgery.

Clinically, these cases may be asymptomatic or present with attacks of dizziness or syncope (Stokes-Adams syndrome), Cannon waves on JVP due to contraction of atria against a closed tricuspid valve(AV discordance), CCF/cardiomegaly, and occasionally sudden death.

Diagnosis is confirmed on ECG, i.e. absence of constant relationship between P waves and QRS complexes.

Treatment: Cardiac pacing with permanent pacemaker is needed only in symptomatic cases with recurrent syncopes, HR lt;40 and cardiomegaly. Otherwise, prognosis is favorable even in untreated cases.

Sick sinus syndrome is characterized by intermittent or alternating attacks of tachycardia and bradycardia, causing palpitation and syncopal attacks. It is most commonly seen after cardiac surgery, though occasionally may also develop in normal children without cardiac disease. Treatment includes insertion of a demand-driven ventricular pacemaker along with drugs to control tachyarrhythmias, e.g. propranolol, quinidine, etc.

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