Larger animals such as elk or moose sometimes seem to be immuned to hydrostatic shock. Tissue damage is what usually kills. Otherwise an arrow with a broadhead wouldn't do much.
As noted, its not tissue damage (and certainly not hydrostatic shock) but very specific damage to the nevrous system or heart and or lungs.
We shot a moose one time that literally bled out over time, but made around 3/4 mile while doing so. It still managed a final lunge at the end at us. Go figure. The butchering was bloodless. We failed to execute a good shot that did the massive quick bleed-out you strive for (I never went for a heat shot though my brother did once and dropped it on the spot).
Saskhunter put it exactly right.
What happens if you hit certain spots and get spastic results is not hydro shock. I never saw that happen and my closest was a small caribous at 60 yards with a 7mm Rem Mag. All I shot continued for a bit and they were all massive lung and or heart damage.