Accelerated Automaticity

As the name suggests this arrhythmia results from accelerated automaticity in the cells of pacemaker and conduction system. Arrhythmias included in the this category are:

1) Sinus tachycardia

2) Atrial tachycardia

3) Accelerated junctional rhythm

4) Accelerated ventricular rhythm

Sinus Tachycardia

Sinus tachycardia is characterized by a rapid (> 100 bpm) rate of discharge of the SA node. The sinus node is discharging at a rate > 100 and the remainder of the conduction follows the normal pathway. The following ECG shows sinus tachycardia.

Sinus Tachycardia

Possible Causes

• Normal cardiac response to demands for increased oxygen need during pain, fever, stress,dehydration and exercise

• Caffeine, nicotine ingestion

• Hyperthyroidism

• Post MI or early sign of heart failure

ECG Criteria

1) Heart Rate: > 100 bpm to 160 bpm,in children can go upto 220 bpm

2) Rhythm: Regular

3) P-waves: Upright and normal. One P precedes every QRS

4) PR Interval: .08 -.20 seconds

5) QRS Width: < 0.12 seconds

Junctional Tachycardia

Junctional rhythm greater than 100 bpm is called Junctional Tachycardia. The SA node is not working and the junction has taken over as the pacer, only a bit faster than its normal intrinsic rate of 40-60 bpm.

Possible Causes of Accelerated Junctional Rhythm

• Digoxin toxicity (most common cause)

• Hypoxia

• Cardiomyopathy

• MI

• Valve replacement surgery

ECG Criteria of Accelerated Junctional Rhythm

1) Heart Rate: > 100 bpm.

2) Rhythm: Ventricular rhythm is regular.

3) P-waves: may be absent or may occur before, during or after the QRS (due to retrograde conduction).

4) PR Interval: None (impulses are originating from the junction, not the SA node).

5) QRS Width: < 0.12 seconds (the impulse is traveling down the normal pathways of the right and left bundles.

Paroxysmal Atrial Tachycardia

Ectopic, discrete looking, unifocal P’-waves with atrial rate <250/minute (not to be confused with slow atrial flutter). Ectopic P’-waves usually precede QRS complexes with P’R interval < RP’ interval (i.e., not to be confused with paroxysmal supraventricular tachycardia with retrograde P-waves appearing shortly after the QRS complexes). Ventricular response may be 1:1 or with varying degrees of AV block (especially in digitalis toxicity).

Paroxysmal Atrial Tachycardia

Multifocal Atrial Tachycardia (MAT) and Rhythm

Discrete, multifocal P’-waves occurring at rates of 100-250/min and with varying P’R intervals(should see at least 3 different P-wave morphologies in a given lead). Ventricular response is irregularly irregular (i.e., often confused with A-fib). May be intermittent, alternating with periods of normal sinus rhythm. Seen most often in elderly patients with chronic or acute medical problems such as exacerbation of chronic obstructive pulmonary disease.

Accelerated Ventricular Rhythms

An “active” ventricular rhythm due to enhanced automaticity of a ventricular pacemaker(reperfusion after thrombolytic therapy is a common causal factor). Ventricular rate 60-100 bpm (anything faster would be ventricular tachycardia). Sometimes called isochronic ventricular rhythm because the ventricular rate is close to underlying sinus rate. May begin and end with fusion beats (ventricular activation partly due to the normal sinus activation of the ventricles and partly from the ectopic focus). It is usually benign, short lasting, and not requiring any treatment.