The monitor, the size of a thumbnail, is placed under someone’s skin during minor surgery and measures the pace, rhythm and ‘electronics’, of the heart, which can be seriously affected after a heart attack.
During and after a heart attack, heart muscle is starved of oxygen and nutrients, and can be severely damaged. To measure the extent of this damage, cardiologists measure the heart’s ‘ejection fraction’. This is the proportion of blood that a specific chamber of the heart - the left ventricle – pushes out or ‘ejects’ into the body's circulation per heartbeat. If this is below 35 per cent, the damage is considered extensive and dangerous complications like serious heart rhythm disturbances become common. To treat this, someone will usually receive an implanted cardioverter defibrillator (ICD) as a preventive measure. If the ICD detects a dangerous abnormal heart rhythm, it automatically delivers a life-saving electrical shock to bring the heart back into correct rhythm.
However, there is a group of patients who may not qualify for an ICD, as their ejection fraction is above 35 per cent, but will still have suffered serious heart damage and remain at high risk of fatal complications. To address some of these patients, the focus of the study was on those who had an ejection fraction of between 36 and 50 per cent and who had significant nerve damage in the heart after their heart attack. These patients are particularly at risk for arrhythmias and other complications.
"These patients still have hearts with relatively good output, yet many of them suffer life-threatening complications," says study leader Prof. Axel Bauer from the Medical University of Innsbruck.
Serious complications in patients who still have relatively good heart output
"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 per cent, for whom there are no specific preventive measures," says Bauer. Previous studies with patients who had severely lowered heart function showed that early, unpredictable abnormal heart rhythms that go un-noticed in conventional follow-up can often lead to severe complications. The SMART-MI-DZHK9 study has now investigated whether implantable monitors can detect such early ‘arrhythmias’.
The 400 patients were divided into two groups – One group was monitored remotely using the heart monitor, while the control group received standard follow-up care, face-to-face. The researchers predefined the sort of rhythm or electrical abnormalities that would cause concern and set about measuring how often they were spotted in each group. The heart-monitor detected the abnormalities in 60 patients over 21 months, while conventional methods detected them in just 12 patients over the same time period.
The patients in both groups received the appropriate diagnoses and treatments, in accordance with standard guidelines. Follow on treatment ranged from surgically implanting ICDs or pacemakers or the use of catheter ablation to remove the damaged heart or nerve tissue, to less intrusive electrophysiological examinations (eg ECG) or treatment with blood thinners.
Treat ‘intermediate’ patients as if they had more severe symptoms
The patients studied appeared to have a similar risk profile as those with a severely reduced ejection fraction, so the researchers suggest that both groups should receive similarly intensive follow-up care. Prof. Bauer added: "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."
The study could not yet determine whether early treatment of these warning signs will prevent fatal or severe complications in the long term, as that was beyond the scope of this research
ESC Congress 2021, 27. August 2021, Hot line Session:
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, Medizinische Universität Innsbruck
Study title: Implantable cardiac monitors in high-risk post-infarction patients with cardiac autonomic dysfunction SMART-MI-DZHK9
Prof. Axel Bauer, Medizinische Universität Innsbruck, Universitätsklinik für Innere Medizin III - Kardiologie und Angiologie, axel.bauer(at)tirol-kliniken.at
Christine Vollgraf, Press and Public Relations, German Center for Cardiovascular Research (DZHK), phone +49 30 3465 52902, firstname.lastname@example.org