ACCELERATED JUNCTIONAL RHYTHM

Case: 25 year old female having a diagnosis of cyanotic congenital heart disease presented with acute lower respiratory tract infection. On examination she had central cyanosis, clubbing, kyphoscoliosis, dextrocardia, situs inversus, pulmonary stenosis, ventricular septal defect, double outlet right ventricle, right ventricular hypertrophy and transposition of great arteries.

Fig-1: ECG of a 25 year old female having dextrocardia, situs inversus and congenital cyanotic heart disease.

ECG showed tachycardia (ventricular rate 100 beats/minute), inverted p wave in all leads except aVR, V1 and V2, normal PR interval, narrow QRS complex and T wave inversion in all leads. These ECG findings are in favour of accelerated junctional rhythm.

Answer: Accelerated junctional rhythm

Discussion:

Accelerated junctional rhythm (AJR) occurs when the rate of an AV junctional pacemaker exceeds that of the sinus node. This situation arises when there is increased automaticity in the AV node coupled with decreased automaticity in the sinus node. Causes of AJR are digoxin toxicity, use of beta-agonists, e.g. isoprenaline, adrenaline, Sick sinus syndrome, myocardial ischaemia, myocarditis (acute rheumatic fever, lyme disease, Diphtheria) and metabolic states with increased adrenergic tone. Certain drugs which can cause bradycardia such as beta blockers, calcium channel blockers and antiarrhythmic agents can also induce AJR.

Junctional rhythms are classified by their rate as 1) Junctional Escape Rhythm: 40-60 bpm 2) Accelerated Junctional Rhythm: 60-100 bpm and 3) Junctional Tachycardia: > 100 bpm.

They may also be classified by aetiology as automatic Junctional Rhythms (e.g. AJR) = Due to enhanced automaticity in AV nodal cells or re-entrant Junctional Rhythms (e.g. AVNRT), due to re-entrant loop involving AV node.

Fig-2: Example of an accelerated junctional rhythm (courtesy ECG library)

ECG Features of AJR

·         Narrow complex rhythm; QRS duration < 120ms (unless pre-existing bundle branch block or rate-related aberrant conduction).

·         Ventricular rate usually 60 – 100 bpm.

·         Retrograde P waves may be present and can appear before, during or after the QRS complex.

·         Retrograde P waves are usually inverted in the inferior leads (II, III, aVF), upright in aVR + V1.

·         AV dissociation may be present with the ventricular rate usually greater than the atrial rate.

·         There may be associated ECG features of digoxin effect or digoxin toxicity.

Periods of junctional rhythm are not necessarily associated with an increase in mortality. If an obvious cause is present, such as complete heart block or sick sinus syndrome, then the morbidity or mortality is directly related to that and not to the junctional rhythm mechanism, which is serving as a "backup rhythm" during the periods of bradycardia. Accelerated junctional rhythms may be a sign of digitalis toxicity.

ECG features may be mistaken for that of dextrocardia as this patient is having dextrocardia and situs inversus. In dextrocardia inverted P wave is seen only in Lead-1 and upright P in aVR. Other features are right axis deviation, positive QRS complexes (with upright P and T waves) in aVR, inversion of all complexes (global negativity) in Lead I and absent R-wave progression in the chest leads.

Complications

Complications of junctional rhythm are usually limited to symptoms such as dizziness, dyspnea, or presyncope. Exacerbation of cardiac comorbidities, such as congestive heart failure and rate-related cardiac ischemia, may occur.