Abnormalities of cardiac rhythm such as atrial fibrillation (AF), supraventricular tachycardias, bradycardia and ventricular arrythmias, are associated with significant morbidity and economic burden. In scenarios where an arrythmia is difficult-to-diagnose, cardiac rhythm monitoring could prove to be beneficial for diagnostic assessment and therapeutic intervention especially in patients who present with palpitations, syncope or cryptogenic stroke [1–3]. Electrocardiography (ECG) serves as the gold standard for non-invasive monitoring of cardiac rhythm and conduction disturbances. However, the frequently utilised 12-lead ECG provides seconds of cardiac rhythm monitoring which is inadequate largely due to lack of symptoms during ECG assessment. Although, other non-invasive systems such as external loop recorders, wireless patch monitors and mobile cardiac telemetry system are useful in standard clinical practice, they can be bulky and limited in providing extended cardiac rhythm surveillance yielding low patient compliance or even more concerningly, low detection rates for silent arrythmias .
Insertable cardiac monitors (ICMs) are currently established as significant counterparts in the diagnosis of arrythmias with greater than 78% detection rates, thus providing a correlation between heart rhythm and cardiac symptoms [5, 6]. With regards to syncope and cryptogenic stroke, landmark studies including CRYSTAL-AF , PICTURE[7, 8] and others [9–12] have now consistently shown the safety and efficacy of ICMs in the diagnosis of arrythmias or AF with a detection rate of ~10-30% compared to non-ICM control arms. ICMs have also been useful as an exclusion tool in the diagnosis of arrythmias thereby enhancing standard-of-care [13, 14]. The FRESH study reported a definite cause of syncope in 46% of the ICM group compared to 5% in the conventional group (suggestive of greater than 40% additional benefit with an ICM). Reinforcing the study’s results, no differences were reported in quality of life between the two treatment arms possibly due to less cardiac testing in the ICM group .
Despite the past decade’s advancements in diagnosis of arrythmias and AF by ICMs, some limitations such as sub-optimal ECG, short memory storage and risk of procedural complications, have hindered diagnosis in patients presenting with syncope or cryptogenic stroke. The main limitation being the inability to obtain clear and accurate subcutaneous ECG in prolonged monitoring leading to artefacts and non-diagnostic interrogations. A QRS or R wave under-sensing and oversensing may reflect false asystole and false high ventricular rate episodes, respectively [15, 16] and thus, mislead diagnosis. Although, recommendations for optimal positioning and procedural methodologies for implanting ICM have been investigated and provided some success, patient-specific features and complexity of cardiac pathologies have confounded further progress, particularly for arrythmias/AF arising from syncope and cryptogenic stroke [17, 18].
This study was performed to address one such cause of limitation in ICM-based arrythmia detection, patient body postures and movements. Body postures have increasingly gained attention following findings from a comparative study of surface and subcutaneous ECGs’ by Bellardine Black et al. (2010) . It was reported that in an assessment of 12 controlled body postures and movements, surface ECGs were an adequate surrogate of subcutaneous ECGs during resting and isometric myopotential noise conditions. However, in situations of patient movement, surface ECGs was not representative of subcutaneous ECG owing to significantly worse signal to noise ratio. This study also demonstrated intra-patient variability in R-wave amplitudes (RWAs) due to common body postures in patients clinically indicated for an ICM. Here, we present findings on fifteen separate controlled body postural activities immediately following implantation with the Confirm Rx™ ICM (Abbott Medical Devices, Australia).