I find this interesting. Along with the Christian Eriksen situation, too. I've been lurking for ages, but this prompted me to sign up.
Back in 2011, I had a heart attack. 2 stents later, I'd lost 25% of my heart muscle /efficiency, but had a decade of no further issues.
Recently, I'd been getting the atrial fibrillation (AF) issues as seen in Tom Lockyer during the playoff final. I was booked in for an ablation (which is what I assume he had), but we couldn't trigger my AF in the theatre, so couldn't ablate.
However, what we did trigger was a ventricular tachycardia (VT) which nearly caused me to black out and we were seconds from shocking me (they already have the pads on when you're undergoing procedures like this). Fortunately I didn't need this and came back myself. I've since had another 2 stents done to try to protect me from restricted blood flow.
Without wanting to feed rumours, it looks like this is what happened to Tom today - he went into ventricular tachycardia but couldn't recover from it, this crashes your blood pressure and often leads to arrest.
Fortunately, on the pitch in a football stadium is one of the better places for this to happen - you have medics and a defibrillator on site - as we saw with Eriksen and previously with Muamba.
Unfortunately, this often happens when you're alone or asleep, so you never get the help before it kills you.
I assume Tom Lockyer will now have to have an ICD (defibrillator / pacemaker) like Eriksen - which could allow him to continue playing. I hope to have one implanted in the new year as an insurance policy for me.
However, you can imagine what this has done for my anxiety levels this evening!
The problem is that these things are hard to diagnose - and the diagnosis process is quite stressful, involving adrenaline injections which come with their own risk (see above ref my failed ablation - it was the adrenaline that pushed me into VT). Hearing the nurse call 'he's in VT, 300 joules, stand clear' is not what you want to hear!