Thanks to Dr. Amal Mattu for sharing his ECGs with me from his University of Maryland ECG archives . If you haven't heard of this amazing ECG video series, you should definitely check it out.
Below is the video teaching this point within the topic of narrow-complex regular tachycardias. This trick is seen at the 15:00 minute mark.
For another example, check out Dr. John Larkin's blog ECG of the Week post on a pediatric SVT rhythm at 300 bpm with no P waves seen at 50 mm/sec.
Accardi AJ, Miller R, Holmes JF. Enhanced diagnosis of narrow complex tachycardias with increased electrocardiograph speed. J Emerg Med. 2002 Feb;22(2):123-6. Pubmed
Gaspar JL, Body R. Best evidence topic report. Differential diagnosis of narrow complex tachycardias by increasing electrocardiograph speed. Emerg Med J. 2005 Oct;22(10):730-2. Pubmed Free PDF