Which of the following best describes the contraction of the cardiac cells from the electrical discharge?

Tachyarrhythmias may be divided into 4 groups, defined by the QRS complexes:

• Visibly regular vs irregular

• Narrow vs wide QRS complexes

Irregular, narrow QRS complex tachyarrhythmias include the following 4 rhythms. Differentiation is based on atrial ECG signals, which are best seen in the longer pauses between QRS complexes.

• True atrial tachycardia with variable AV conduction: Regular, discrete, uniform, abnormal atrial signals with intervening isoelectric periods (usually at rates < 250 beats/minute)

Irregular, wide QRS complex tachyarrhythmias include

• The above 4 irregular, narrow atrial tachyarrhythmias conducted with either bundle branch block or ventricular preexcitation

• Polymorphic ventricular tachycardia (VT)

Differentiation is based on atrial ECG signals and the presence in polymorphic VT of a very rapid ventricular rate (> 250 beats/minute).

Regular, narrow QRS complex tachyarrhythmias include

Vagal maneuvers or pharmacologic AV nodal blockade can help distinguish among these tachycardias. With these maneuvers, sinus tachycardia is not terminated, but it slows or AV block develops, disclosing normal P waves. Similarly, atrial flutter and true atrial tachycardia are usually not terminated, but AV block discloses flutter waves or abnormal P waves. The most common forms of paroxysmal SVT (AV nodal reentry and orthodromic reciprocating tachycardia) must terminate if AV block occurs.

Regular, wide QRS complex tachyarrhythmias include

• The above 4 regular, narrow QRS complex tachyarrhythmias conducted with bundle branch block or ventricular preexcitation

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Genetic disorders causing cardiac arrhythmias in the absence of structural heart disease (Primary Electrical Disease)