Excerpt

The application of phase analysis most likely originated with software algorithms used to define the atrioventricular plane in equilibrium radionuclide angiograms (ERNA) for the purpose of calculating the left ventricular ejection fraction. That application was intuitive since the left atrium and left ventricle are 180° out of phase. Given adequate count statistics to generate reliable Fourier transforms, the technique is quite robust. Early on, the first clinical applications used phase analysis to identify the timing of the onset of mechanical contraction using ERNA in order to characterize electrical phenomena that caused either delays in contraction (LBBB, RBBB) or premature mechanical contraction (site of pre-excitation in WPW, site of origin of ventricular tachycardia). However, despite the elegance of the approach, its application did not gain traction in clinical cardiology. At the time, electrophysiology as a clinical discipline was in its infancy and with its maturation, there was really no need for other noninvasive techniques to demonstrate the location of a Kent bundle or the site of earliest activation during ventricular tachycardia. And so, phase analysis was relegated to the file of curios, something to show trainees or dredge up for an exam. …