On New Year's Eve of 2019 Sandra McCartney was clinically dead for 10 minutes.

She was 59 when she collapsed during a Christmas holiday in Spain, lost consciousness, stopped breathing and had no pulse or heartbeat after suffering a cardiac arrest.

Sandra's life was saved when medics managed to restore a normal heart rhythm during a frantic race against time when paramedics gave her "six defibrillator shocks and five shots of adrenaline".

Her life may have been turned upside down in that moment but she believes she had been living with a ticking time bomb long before that.

Sandra found out that the heart attack and cardiac arrest were triggered by a life-threatening genetic condition called "familial hypercholesterolaemia" (FH).

It causes high cholesterol and, if untreated, can lead to early heart attacks and heart disease.

The mother-of-four, from Londonderry, did not even know she had it.

And she is not alone.

The British Heart Foundation estimates that more than quarter of a million people in the UK have the condition, but more than two-thirds of people who have FH are never diagnosed.

However, Northern Ireland has the highest detection rate in the UK.

The experience is something that has left its mark on Sandra.

"I had three cracked ribs from the CPR (cardio-pulmonary resuscitation) and I was gone for 10 minutes before they got me back, which is terrifying to think about."

On the night she took ill, Sandra thought she had indigestion because of her "hiatus hernia" - a condition common in the over-50s, where part of the stomach moves up towards the stomach.

She alerted her husband when she began to feel an acute pain followed by a tingling sensation in her right arm.

As he tried to check if the local health centre was open in the middle of the night Sandra's pain left her and she started "drifting off".

"I was just falling into a deep sleep and he woke me, roaring at me, and shook me," she said.

She was told by a doctor she was having a major heart attack.

Familial hypercholesterolaemia (FH) is quite a common genetic condition, affecting about 1 in every 250-500 people in the population, but many people do not know they have it.

If one parent has FH, there is a 50% chance their child could have it, too.

FH can be very dangerous if left untreated, as it can lead to very high cholesterol, raising the risk of heart attacks or strokes.

Fifty per cent of men and 30% of women with untreated FH will develop coronary heart disease by the age of 55.

The good news is FH can be diagnosed quite easily and there are treatments available.

A screening service operates in Northern Ireland to provide testing for family members of people who have FH to detect as many carriers of the genes as possible.

Source: Northern Ireland Chest Heart and Stroke

She was ventilated for 11 days in hospital and her four children flew out to Spain as it was feared the worst might happen.

"I remember nothing until day four when I was brought round but a few hours later, I was ventilated again because both my lungs collapsed," she said.

"I was woken four days later but I then developed laryngeal stridor, which makes your breathing noisy and harder to do, and which is potentially life-threatening, due to being ventilated too quickly, too many times. I then had to be ventilated again. "

It was not until February that she was allowed to fly home.

Even then she had to use a wheelchair, as she had experienced so much muscle wastage over her time in hospital.

She said it was a "horrendous," not just for her but for her husband and children.

"Never in a million years did I think something like this could happen to me.

"I was fit, healthy, ate really well, I had no worries about my health."

When she returned home she had more problems.

"I wasn't home long when I passed out one day and had to be admitted to Altnagelvin Hospital for a week.

"The pandemic started soon after I was discharged so unfortunately, I didn't get any cardiac rehab which would have been so beneficial to my recovery."

She has also suffered from PTSD (post-traumatic stress disorder) and has an ICD (implantable cardioverter defibrillator) fitted which is a small electrical device because I'm at high risk of having another cardiac arrest."

Sandra's heart attack and cardiac arrest continue to affect her life to this day and there are still days when she can "do very little".

Even "something as simple as throwing a duvet on the bed", can leave her breathless.

She has never been able to return to work, though she volunteers with NI Chest Heart and Stroke and enjoys sewing.

But she is upbeat and grateful to be alive.

"Not many people survive what my body put me through."

All four of her children have tested clear for high blood pressure.

The Belfast Health Trust operates a screening service for what it calls a "silent condition".

"When someone is diagnosed with FH, their relatives are contacted and offered testing by a team of specialist nurses who cover all of Northern Ireland," a spokesperson said.

"Thanks to this programme, Northern Ireland has the highest rate of identification of FH in the UK and one of the highest rates of diagnosed cases in the world."

The trust said that once people are diagnosed and established on long-term treatment with standard cholesterol-lowering medications, they do not generally need further intervention beyond "periodic cholesterol checks".

A cardiac arrest happens when an electrical malfunction stops the heart from beating and circulating blood to the brain and vital organs - often causing permanent brain damage within minutes and sudden death.

A heart attack is not the same as a cardiac arrest.

A heart attack is when one of the coronary arteries becomes blocked. The heart muscle is robbed of its vital blood supply and, if left untreated, will begin to die because it is not getting enough oxygen.

A cardiac arrest is when a person's heart stops pumping blood around their body and they stop breathing normally.

Many cardiac arrests in adults happen because of a heart attack.