It is confusing to mix SVT in with other types of arrhythmias. It is also confusing the mix them in with other types of tachycardia that is any HR above 100 BMP. Ex: Ventricular Tachycardia is not SVT.
See : "What is the difference between ventricular and supraventricular tachycardia?"
"https://www.medicalnewstoday.com/articles/v-tach-vs-svt

SVT is a specific kind of tachycardia. There are 3 main groups of SVT with 5 other types of SVT.
Note: During SVT, the heart beats about 150 to 220 times a minute. See this for a perfect simple explanation of SVTs.
https://www.mayoclinic.org/diseases-conditions/supraventricular-tachycardia/symptoms-causes/syc-20355243
Also for a review on how to perform the valsalva maneuver:
https://my.clevelandclinic.org/health/treatments/23209-valsalva-maneuver
For an in-depth scientific review see:
https://www.ncbi.nlm.nih.gov/books/NBK537248/#:~:text=The%20Valsalva%20maneuver%20is%20forced,balloon%2C%20or%20playing%20the%20saxophone.