In an unusual incident, a fitness tracker ended up saving the life of a 73-year-old woman with large blood clots in her lungs - by indicating a spike in heart rate which allowed her to call for help in time.

Patricia Lauder from the US bought a wearabale fitness tracker hoping to improve her health and lose weight.

"I wasn't feeling well for a few weeks, and thought I might be battling a bad cold or walking pneumonia that I just couldn't kick," said Lauder.

However, all her tests came back negative for pneumonia or any other health issues.
She started to experience shortness of breath and fatigue, while walking even very short distances in her own home.

She noticed that her device was recording a rise in her usual resting heart rate of 68-70 beats per minute by five points a day. Then one day her heart rate spiked to 140 beats per minute.

Lauder called the ambulance, and was taken to the University of Connecticut's John Dempsey Hospital in the US. A CT Scan showed that she was suffering from two large blood clots in her lung arteries.

These clots, known as pulmonary embolisms, were causing her lungs and heart to be stressed and over-pressurised.

Her lung artery pressure spiked to 65, when 25 is normal, while her heart was over-working and had become enlarged.

The mortality rate of a pulmonary embolism is over 30 per cent when it is massive, said JuYong Lee, who treated Lauder.

These risky lung blood clots can over-pressurise the heart, leading the body's blood pressure and oxygen level to drop significantly.

The biggest risk factor for developing a pulmonary embolism is deep vein thrombosis, when a blood clot forms in a vein, most often in the leg, and can travel up to the lungs.