PhD ThesisAtrial fibrillation (AF) is the most common cardiac arrhythmia. It is
distinguished by fibrillating or trembling of the atrial muscle instead of normal
contraction. Patients in AF have a much higher risk of stroke. AF is often driven
by the left atrium (LA) and the diagnosis of AF is normally made from lead V1 in
a 12-lead electrocardiogram (ECG). However, lead V1 is dominated by right
atrial activity due to its proximal location to the right atrium (RA). Consequently
it is not well understood how electrical activity from the LA contributes to the
ECG. Studies of the AF mechanisms from the LA are typically based on
invasive recording techniques. From a clinical point of view it is highly desirable
to have an alternative, non-invasive characterisation of AF.
The aim of this study was to investigate how the LA electrical activity was
expressed on the body surface, and if it could be observed preferentially in
different sites on the body surface. For this purpose, electrical activity of the
heart from 20 patients in AF were recorded simultaneously using 64-lead body
surface potential mapping (BSPM) and bipolar 10-electrode catheters located in
the LA and coronary sinus (CS). Established AF characteristics such as
amplitude, dominant frequency (DF) and spectral concentration (SC) were
estimated and analysed. Furthermore, two novel AF characteristics (intracardiac
DF power distribution, and body surface spectral peak type) were proposed to
investigate the relationship between the BSPM and electrogram (EGM)
recordings.
The results showed that although in individual patients there were body
surface sites that preferentially represented the AF characteristics estimated
from the LA, those sites were not consistent across all patients. It was found
that the left atrial activity could be detected in all body surface sites such that all
sites had a dominant or non-dominant spectral peak corresponding to EGM DF.
However, overall the results suggested that body surface site 22 (close to lead
V1) was more closely representative of the CS activity, and site 49 (close to the
posterior lower central right) was more closely representative of the left atrial
activity. There was evidence of more accurate estimation of AF characteristics
using additional electrodes to lead V1
