Exploration of Arrhythmia Burden in Cardiac Amyloidosis Using Implantable Loop Recorders

Sudden cardiac death (SCD) occurs in up to 1/3 of patients with cardiac amyloidosis but conflicting findings have been reported on the mechanism. Electromechanical dissociation (EMD) is thought to account for some 6-7 cases, underscoring doubts about a role for implantable cardioverter-defibrillators (ICDs). However, there are studies that have described appropriate and effective ICD therapies in 27% to 32% of cases, similar to primary prevention in other disorders. The strength of evidence in all these studies is fairly weak (small, single-centre, retrospective, not linked to mechanism), but this potentially makes ICD implantation more important than in other conditions. It has also been shown in a study with small patient numbers that the pre-terminal event is often bradycardia, which may be amenable to pacemaker therapy. At present, the available information regarding arrhythmia burden in cardiac amyloidosis is limited, and further data are crucial to better guide patient selection for device therapy.

Whilst the burden of arrhythmia and sudden cardiac death appear considerable, there is limited characterisation of the incidence and predictive factors for arrhythmia requiring treatment. Cardiac involvement is the main driver of outcome in cardiac amyloidosis. Amyloidosis is a continuum from small focal amyloid deposits to extensive diffuse myocardial infiltration. The dynamic and progressive nature of amyloid deposition is likely to create an arrhythmogenic substrate that alters over time. For example, patchy amyloid deposits occurring in earlier disease might potentially provide an anatomical substrate enabling re-entry and underlie ventricular tachyarrhythmias, whilst diffuse transmural amyloid deposition may increase risk of AV block and bradyarrythmias. The investigators believe that amyloid deposition will be associated with increased risk of fatal arrhythmias, including AV block, bradyarrhythmias and ventricular arrhythmias. There are no current criteria or arrhythmia risk stratification available to guide device implantation in patients with cardiac amyloidosis. There are also limited data available on predictive disease characteristics that promote arrhythmia

Current monitoring for arrhythmia involves routine 12-lead ECG checks at annual or six-monthly clinic visits. Longer durations of monitoring (24- or 72-hour Holter monitoring or implantable loop recorders, ILR) are undertaken only when clinically indicated. Other cardiac investigations that are routinely performed in cardiac amyloidosis include echocardiography and cardiac magnetic resonance (CMR) imaging.

Current management of arrhythmia is limited to anticoagulation as per the CHADS2VASC score for atrial fibrillation, and permanent pacemaker insertion for standard indications including high degree atrioventricular blocks. There are limited data available to inform insertion of defibrillators, and this is currently assessed on a case by case basis.

Cardiac biomarkers may be helpful in raising clinical suspicion of cardiac amyloidosis patients with known plasma cell dyscrasia and should prompt further investigation with electrocardiogram (ECG) and echocardiography. The combination of cardiac biomarkers serum N-terminal prohormone of brain natriuretic peptide (NT-proBNP) and troponin is useful to stratify prognosis and guide treatment strategies in AL amyloidosis, while NT-proBNP and estimated glomerular filtration rate are used to stratify prognosis in transthyretin amyloid cardiomyopathy (ATTR-CM). In these patients, ECG tends to show low voltage complexes with common observations including repolarisation abnormalities, pseudo-infarction patterns, left anterior hemiblock, ischaemic or non-specific T wave abnormalities, and rhythm disturbances such as atrial fibrillation. Echocardiography shows the cardiac amyloid phenotype is a thick-walled ventricle, small left ventricular chamber volume, valve thickening, atrial enlargement and signs of elevated filling pressures with a restrictive diastolic filling.