Over- and undersensing-pitfalls of arrhythmia detection with implantable devices and wearables

Abstract

Cardiac implantable electronic devices (CIEDs) are a cornerstone of arrhythmia and heart failure detection as well as management. In recent years new kinds of devices have emerged which can be used subcutaneously or worn on the skin. In particular for large-scale arrhythmia monitoring, small, unobtrusive gadgets seem positioned to upend paradigms and care delivery. However, the performance of CIEDs and wearables is only as good as their sensing and detection capacities. Whether for pacing, defibrillation or diagnostic monitoring, the device must be able to process and filter the sensed signal to reduce noise and to exclude irrelevant physiological signals. The demands on sensing and detection quality will differ depending on how the information is applied. With a pacemaker or implantable cardioverter/defibrillator, withheld or erroneous therapy can have severe consequences and accurate and reliable detection of cardiac function is crucial. Monitoring devices are usually used in risk assessment and management, with greater tolerance for isolated artefacts or lower quality of readings. This review discusses sensing and detection and the performance to date by CIEDs as well as subcutaneous and wearable devices.

Keywords: Arrhythmia detection; Defibrillator; Over- and undersensing; Pacemaker; Wearables.

Fig. 1

a Schematic illustration of an electrogram with sensing threshold and sensed R wave. b Example of overly high sensing threshold and resulting undersensing of a true R wave. c Example of overly low sensing threshold and resulting oversensing of noise. All images in Figs. 1 and 2 are from Morschhäuser et al. [42] and reproduced with kind permission from the publisher

Fig. 2

Band pass filters for pacemakers. VES Ventricular Extrasystole

Fig. 3

Automatic mode switch during atrial fibrillation

Fig. 4

Incorrect detection of ventricular fibrillation due to noise

Fig. 5

a True bipolar sensing; b Integrated bipolar sensing. RV right ventricular

Fig. 6

a Myopotential signals (~0.8 mV) are oversensed with the low frequency attenuation on. b Signals (~0.27 mV) are still present but not oversensed. V ventricular, LV left ventricular

Fig. 7

a Right ventricular (RV) sensing with the low frequency attenuation (LFA) filter off in a patient with a replaced ICD system. b RV sensing with LFA Filter on

Fig. 8

Example of subcutaneous implantable cardioverter/defibrillator electrogram

Fig. 9

a Example of atrial fibrillation on insertable cardiac monitor electrogram. b Incorrect detection due to undersensing. VEGM ventricular electrogram using a can to header vector

Fig. 10

Wearable defibrillator electrograms showing a ventricular tachycardia and b atrial fibrillation

Fig. 11

The pulsatile (AC) component of the photoplethysmography signal and corresponding electrocardiogram. In actual use, the AC component is superimposed on the much larger quasi-DC component. PTTf beat-to-beat pulse transit time to the foot of the pulse, PTTp pulse transit time to the peak of the pulse. The pulse landmarks can be used to calculate the normalised pulse contour. From Allen [3], used with permission

Fig. 12

Apple watch tracings showing a extrasystole and b atrial fibrillation