Rapid heartbeats increased in frequency in recent weeks. holding breath used to help, now doesn't. seeing doc soon. what could this be?

Arrhythmia: Your symptoms may be an arrhythmia (irregular beating of the heart). There are many types of arrhythmias, and many are helped by holding breath (or other vagal maneuvers). Will need some monitor during symptoms to get better idea of how to manage. In mean time, abstain from caffeine and use a multivitamin per day, and seek further evaluation, as you are doing.