A supraventricular arrhythmia is one that originates from the His bundle or above. The source of the arrhythmia may be the AV junction, atrium, or within the sinus node itself (Figure 18-1). This category encompasses ectopic complexes both premature and late and as well as a variety of tachyarrhythmias. We’ll first review isolated ectopic supraventricular complexes and rhythms, a subject we introduced in Chapter 15. Then we’ll move on to the broad topic of supraventricular tachycardia (SVT), finishing up with atrial flutter and fibrillation. For the purpose of this discussion, we will consider ventricular conduction as normal, which will result in a narrow QRS complex. We reviewed aberrant conduction in Chapter 16 and we’ll cover the topic of wide complex tachycardia in Chapter 20.
A supraventricular arrhythmia is one whose origin is above the bifurcation of the bundle of His.
An atrial premature complex (APC) originates anywhere in the atrial myocardium outside of the sinus node. The morphology of the P´ wave is either unchanged or different from the normal P wave, which reflects its ectopic location. If the depolarization arises near the sinus node, the configuration will be nearly normal. If originating near the AV node, it will be inverted reflecting retrograde depolarization of the atria. The morphology of the P´ wave in different leads may be notched, biphasic or isoelectric, depending on its source located in either atrium (Figure 18-2). The impulse is transmitted through the AV node and His-Purkinje system as usual, producing a P´R interval that is either normal, or slightly shorter depending on its proximity to the AV node. At times, the premature impulse may find the AV node partially refractory whereupon the associated P´R interval will be prolonged over baseline.
Atrial premature complexes with different P´ wave morphologies, upright (a) and inverted (b).
APCs appear early in relation to the cycle length of the native sinus rhythm. The ectopic atrial depolarization typically depolarizes the SA node, resetting the native rhythm. This produces a post-ectopic pause that is not fully compensatory (noncompensatory) (Figure 18-3). However, if the impulse happens not to reset the sinus node, the post-ectopic pause will be fully compensatory.
An atrial premature complex (APC) that resets the sinus node (a) will exhibit a noncompensatory pause. An APC that fails to reset the sinus node (b) will result in a fully compensatory pause.
Repetitive APCs, or occurring in a pattern