Implanted monitor can predict threatening complications after heart attack

An implanted heart monitor detects more signs of dangerous complications in patients who have survived a heart attack than conventional follow-up care.

Many complications of ejection fraction for which no specific preventive measures exist

An implanted heart monitor detects more signs of dangerous complications in patients who have survived a heart attack than conventional follow-up care. This is the result of a study presented at the Congress of the European Society of Cardiology.

The monitor, the size of a thumbnail, was implanted minimally invasively under the skin of the patients. The focus of the study was on patients who, after surviving a heart attack, had an ejection fraction of between 36 and 50% and cardiac control disorders caused by the autonomic nervous system. "The cardiac output of these patients is still relatively good, but many of them suffer life-threatening complications in the course of the disease," says study leader Prof. Axel Bauer from the Medical University of Innsbruck.

Cardiologists measure the damage to the heart muscle after a heart attack using the ejection fraction, which is the proportion of blood that the left ventricle ejects into the body's circulation per beat. If the ejection fraction is below 35%, the heart muscle damage is considered extensive and complications such as malignant arrhythmias are common. These patients are implanted with a defibrillator as a preventive measure. In the event of dangerous arrhythmias, the defibrillator delivers electrical shocks and restores the heart's rhythm.

Majority of fatal complications in patients with moderate cardiac output

"However, the vast majority of fatal and non-fatal complications after a heart attack occur in the large group of patients with an ejection fraction of more than 35%, for whom there are no specific preventive measures," says Bauer. From previous studies with patients with severely impaired cardiac performance, the researchers know that severe complications can often be preceded by asymptomatic arrhythmias that are not noticed in conventional follow-up. The SMART-MI-DZHK9 study investigated whether implantable monitors can detect such early arrhythmias in patients with moderate cardiac output.

Only those patients were included in whom the ECG also indicated nerve damage due to the infarction, i.e. who had cardiac autonomic neuropathy. These patients are particularly at risk for arrhythmias and other complications. The 400 patients were divided into two groups. The study group was monitored telemedically with a heart monitor, while the control group received normal follow-up care. In the monitor group, the researchers detected predefined severe rhythm events in 60 patients within 21 months, in the control group only in 12 patients.

The patients in both groups then received the appropriate diagnostic and therapeutic measures, which could include the implantation of defibrillators or pacemakers, electrophysiological examinations, catheter ablations or the administration of blood thinners. These measures were carried out by the treating physicians at their own discretion, but in accordance with the applicable guidelines.

Treating patients as well as those with low ejection fraction

Future studies must now investigate how best to prevent fatal or severe complications in this group of patients in the long term by treating the arhythmic precursors at an early stage. However, since the patients studied have a similar risk as those with a severely reduced ejection fraction, they should also be followed up intensively accordingly, says Prof. Bauer: "Our study supports the use of implanted cardiac monitors in high-risk patients after a heart attack with moderately reduced ejection fraction and cardiac autonomic dysfunction as a sensitive instrument for continuous risk monitoring."

Implantable cardiac monitors in high-risk post-infarction patients with cardiac autonomic dysfunction and moderately reduced left ventricular ejection fraction - A randomized trial | Axel Bauer, Medical University of Innsbruck, ESC, 27 August 2021.