Narrow complex tachycardias with a regular rhythm*
Sinus tachycardia: The heart rate is typically less than 160 bpm, the QRS complexes show a regular pattern, and upright p waves are clearly visible in leads II and V1.
The distinguishing feature of this arrhythmia is the ramping up and ramping down of the heart rate. The tachycardia is typically less than 160 bpm. But the rate doesn’t suddenly jump from, say, 70 to140 bpm in a flash while the patient is lying in the hospital bed. A trip to the telemetry room for a look at the telemetry strip will tell the tale: The heart rate will have progressively ramped up from 70, to 80, then 90, then 100, 110, 120, 130, to perhaps 140 bpm. And then it will similarly ramp back down in stages, with the up/down pattern being repeated.
Sinus tachycardia is generally a reflection of underlying significant systemic illness, such as sepsis, hypotension, or anemia.
Atrial tachycardia: The heart rate is generally 100-140 bpm, and p waves are present. But unlike in sinus tachycardia, the patient with atrial tachycardia lying in bed with a heart rate of 140 bpm is not in a state of profound neurohormonal activation and is not all that sick.
Another diagnostic clue is provided by a look at the telemonitoring strip. Unlike in sinus tachycardia, where the heart rate ramps up and then back down repeatedly, in atrial tachycardia the heart rate very quickly ramps up in stages to, say, 140 bpm, and then hangs there.
Atrial flutter: This is the only narrow complex tachycardia that appears in both the regular and irregular rhythm columns. It belongs in the irregular rhythm column when there is variable conduction and cluster beating, with a regularly irregular pattern of RR intervals. In contrast, when atrial flutter is in the regular rhythm column, it’s because the atrioventricular node is steadily conducting the atrial depolarizations at a rate of about 300 bpm. So there’s no cluster beating. As in atrial flutter with variable conduction, the flutter waves are visible most often in leads II, III, and aVF, where they can be either positively or negatively deflected.
AV reentrant tachycardias: These reentrant tachycardias can take two forms. In atrioventricular nodal reentrant tachycardia (AVnRT), the aberrant pathway is found entirely within the AV node, whereas in atrioventricular reentrant tachycardia (AVRT) the aberrant pathway is found outside the AV node. AVnRT is more common than AVRT. As in atrial flutter, there is no ramp up in heart rate. Patients will be lying in their hospital bed with a heart rate of, say, 80 bpm, and then suddenly it jumps to 180, 200, or even as high as 240 bpm “almost in a split second,” Dr. Walsh said.
No other narrow complex tachycardia reaches so high a heart rate. In both of these reentrant tachycardias the p waves are often buried in the QRS complex and can be tough to see. It’s very difficult to differentiate AVnRT from AVRT except by an electrophysiologic study.
Accelerated junctional tachycardia: This is most commonly the slowest of the narrow complex tachycardias, with a heart rate of less than 120 bpm.
“In the case of accelerated junctional tachycardia, think slow, think ‘regular,’ think of a rate often just over 100, usually with p waves after the QRS that are inverted because there’s retrograde conduction,” she advised.
She reported having no financial conflicts of interest regarding her presentation.
Correction, 8/19/20: An earlier version of this article mischaracterized the type of rhythm noted in this subhead.
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