Final answer:
Cardiac arrest after spinal anesthesia can occur due to sustained ventricular contraction and respiratory paralysis, induction of coma and lowered body temperature, and large electrical currents causing the heart to stop beating temporarily.
Step-by-step explanation:
Cardiac arrest after spinal anesthesia can occur due to several mechanisms. One possible mechanism is the onset of sustained ventricular contraction and respiratory paralysis, which can cease when the shock ends. Another mechanism is the induction of coma and lowering of the patient's body temperature, which reduces the heart's workload. Additionally, very large currents can cause the heart and diaphragm to contract, leading to temporary cardiac arrest.