<prompt> Which of the following can be used to calculate hea rate from an ECG?Number of large squares in one R-R interval300300 Number of large squares in one Q-T interval300 Number of large squares in one R-R intervalNumber of large squares in one Q-T interval 300  <response>: For calculating hea rate: HR-300 Number of large squares0.20 secs in one R-R interval HR-1500no of small squares 0.04 secs in one R-R interval 