I'm 81, have SVT, and have a different vagul maneuver I recently discovered that I want to share. It has worked 100% of the time so far for me to bring me back to normal HR. (That's about 14 times so far). Not nearly as sophisticated as you, and apparently simpler, I use it whenever I notice that I'm experiencing unexplainable rapid heartbeats (usually less than 120 bpm when it first catches my attention). No need for me to try to measure the exact heart rate; two fingertips on the main artery on the side of the neck and count the # of beats per minute is enough for me to decide I'm having an episode. Then I do this:
1) Big inhale to a count of 4
2) Hold your breath for a count of 7.
3) Exhale to a count of 8
4) Repeat the above steps three more times only.
Usually I'm back to normal rhythm by step #3. Sometimes it'll last until 3-5 minutes after the maneuver, bt never longer ("knock on wood"). Hope this works for some of you.
Oh ... I've been taking 25mg of Metoprolol daily for almost two years and carry a few more pills for "pill in pocket" use as needed, but thanks to the vagul maneuver, I've never had to use the P-I-P.