No clinical history. What is the rhythm?
Figure 1 - Tachyarrhythmia case
This is a regular narrow QRS complex tachycardia at a rate of about 136 bpm. This is loosely called supraventricular tachycardia (SVT). There are several differential diagnoses for SVT ranging from AV nodal reentry tachycardia (AVNRT), atrial flutter, etc. In monitored settings, the beginning of the arrhythmia can be captured and reviewed.
Figure 2 - Initiation of the arrhythmia
This arrhythmia is initiated by a premature atrial complex (PAC) and distinct P waves can be seen during the tachyarrhythmia. A few seconds or minutes later, these P waves will merge with the T waves. There will be some "cool-down" in the rate when some P waves will again be seen. Thus, this is atrial tachycardia (AT). Catching the beginning of the tachyarrhythmia makes our work easier and removes all the guesswork.