Dear friend,
                It is sruprising that you can opt for echo but you dont have anaesthesia machine ( i suppose as you have mentioned you dont have good set-up). 2.5 ml in cardiac patient is too much. you could have used less amount with addition of tidigesic, morphine or fentanyl if you have.
Continuous spinal or epidural would have been ideal choice, i have used continuous spinal in such cases my self, without complications.

 Dear friend,
how circulating catecholamine will cause uterine contracture(severe contraction) we all know B1 stimulation is having tocolytic effect. The brady cardia is due to withdrawl of catecholamine after sudden relief of pain, which causes bradycardia. It is short lived and will not harm baby any way.