Dear Sir/ Ma'm
thanks for posting your query.
An intermittent racing like this which is increasing is likely to be an arrhythmia
. details of which can only be discussed after looking at an ECG which was obtained at time of event. An ECHO will tell if a structural heart disease
is responsible for it or not. it may come out to be entirely normal. You have not mentioned your age? was your BP found to be higher than 140/90 mmHg on other occasions too? did you ever get blackout
or lost consciousness during these episodes? if the answer to last question is NO, than relax. this is not likely to be one of the most dangerous of rhythm disorders.
one more thing, did they check your THYROID
please revert back with these answers for more clarifications.