What will be the pulse rate in a patient who has ventricular bigeminy in ECG with a heart rate of 90 ( 45 sinus beats 45 VPDS/minute ) ?
A.Exactly Same as HR , ie 90/mt
B.Exactly half of HR , ie 45/mt
C.Can be anything between 45 to 90/mt
D.Any of the above can be true
The answer is D .
I have noted ,this simple question in cardiology resident examinations cause great anxiety among students .
Why is it difficult to arrive at an easy answer to this question ?
Traditionally , ventricular ectopic beat were also called extrasystole , implying every ectopic beat shall produce a peripheral pulse .Since , we learnt this is not true , we started refering them as VPDs.(Simple ventricular depolarisation which may or may not have a mechanical activity ) So , in a patient whose alternate beat is a VPD , things become little complicated.
What determines a VPD to acquire mechanical energy or simply remain as an electrical event ?
Timing of the VPD* .
LV residual volume(LVEDV ) at the onset of VPD
Force of contractility of LV( Of course , it is directly related to LVEDV)
Temporal relation to aortic valve opening**
If the VPD is too early or too late it can not have a mechanical activity . It should be optimally timed midway between two sinus beat to have a good mechnically active VPD. Some refer this as an interpolated VPD .Here, the VPD becomes a true extra systole for that individual. So , in patient with ventricualr bigeminy in ECG the pulse rate is usually half , can be same as HR when the coupling interval is optimal or it can be totally irregular as someof the VPDS gain a mechanical activity and some do not (as often occurs multifocal VPDs. )
* Among the above four factors timing of the VPDS is the most crucial as it can influence all the other three factors.
** Whatever be the timing or force of contraction aortic valve should be opened to generate a pulse wave. If for some reason this does not happen there can be intermittent mechanial activity what we refer to as pulse deficit .
Read a related phenomenon: Ventricular paired pacing
Can having these types of beats constantly as ones regular beat be dangerous. I was at the ER last night and the ekg they gave me came up with bigeminy It was my pattern for the whole test (however it was just a basic 1min ekg test) . The doc. did not seem concerned at all, was he correct in saying so. Can these be simple picked up on a stethoscope, i was in to my family doc. today and he listened to my heart and said it sounded perfect (could not hear any abnormal beats/pvcs). Also not to worry about my test, he is going to send me to a cardiologist as protocol he said when any patient has any irregular beats on their ekg test. thanks for any advice