Sudden cardiac arrest is a killer. According to the CDC, approximately 209,000 people in the U.S. are treated for in-hospital cardia arrest (IHCA) annually. Those were the lucky ones, because they were already in the hospital. In 2015, for example, about 357,000 people experienced out-of-hospital cardiac arrest (OHCA). Again according to the CDC, OHCA has a mortality rate of 70 to 90%. Plus OHCA survivors often have resultant brain injury, other physical problems, and psychological issues. External defibrillators can save lives if applied immediately after cardiac arrest, but fast action is essential. Some — but not all — high-risk patients benefit from Implantable cardiac defibrillators (ICD). According to a 2019 German Heart Surgery Report, relatively common complications can negate the benefit of the implants but the challenge is finding a way to identify who will be helped by an ICD.

A new study reports that nocturnal breathing rate can indicate which ICD candidates are less likely to benefit from the implants. Researchers at the Technical University of Munich (TUM) recently published a study in EClinicalMedicine that reports the results of their inquiry. The bottom line is this; patients who breathe an average of 18 or more times per minute during the night are at greater risk of non-arrhythmic death associated with implants. The risk level for those patients negates the ICD benefit.

Between 2014 and 2018, the TUM researchers monitored 1,971 heart patients at 44 European heart centers; 1,363 of them had ICDs, The researchers monitored average nocturnal respiratory rates of all subjects from midnight to 6 A.M. While overall the ICD recipients had a 31.3% greater survival rate than the patients who did not have implants, the nighttime breathing rates were a significant differentiator. The survival rate of ICD recipients who had breathing rates less than 18 times a minute had a 50% survival rate, but implant patients with higher respiratory rates did not have a significantly greater chance of survival than patients who did not have implants.

The implications of the TUM study suggest that wearable devices that measure breathing rate can assist cardiac physicians decide whether to recommend ICDs for high-risk patients. The TUM study was not randomized, so further study is necessary. If future randomized studies replicate the TUM results, physicians would have a basis on which to recommend against ICDs for patients with relatively high nighttime breathing rates.