Pilot Pete
You are obviously very fit, and in the absence of any other significant medical history, there is nothing to worry about at this time. Its not like its medication induced, in which case your cardiac reserve would be depleted.
You are maintaining a great blood pressure, with what sounds like great stroke volume ie your heart whilst it is beating 'slower' actually has more time to fill with blood between beats. Its called 'Starlings Law'.
There is evidence that later in life this can pre-dispose you to "athletes heart" and potential electrical conduction abnormailities of you myocardium (heart muscle) usually in the form of Sino-atrial arrest (pauses). But whilst you are still young - enjoy.
