Understanding the ECG. Part 5: Pre-excitation

Understanding the ECG. Part 6: QRS axis

“…Electrical activation of the ventricles has perhaps the greatest effect on QRS axis (Bennett, 2013). We know from our discussions of bundle branch blocks and pre-excitation that abnormalities in conduction can alter the pattern of depolarisation in the ventricles (Sampson, 2016a;Sampson, 2016b). These abnormalities can also alter the QRS axis, although Garcia (2015) suggests that this rarely occurs due to bundle branch block.…”

Understanding the ECG. Part 7: Chamber enlargement

“…We need to remember that pre-excitation alters the electrical activation of the ventricles, and therefore the shape of the QRS complexes (Maden et al, 2015). Pre-excitation can alter normal R-wave progression, and cause axis deviation (Sampson, 2016c). Patients with pre-excitation need specialist evaluation because of an increased risk of arrhythmias and sudden cardiac death (Obeyesekere et al, 2012).…”