Nuclear electrophysiology

Correlations between cardiac imaging and electrophysiological studies: what is the state of the art?

Changes in ventricular activation produced by bundle branch block, pre-excitation, and ventricular tachycardia and pacing have been studied by various cardiac imaging modalities. We reviewed results of previously published and newly generated imaging data correlated with known or measured electrophysiological studies. Echocardiography has been demonstrated to grossly correlate with abnormal ventricular wall motion when activation sequence was altered. However, phase analysis of radionuclide and cine-computed tomography have provided detailed noninvasive activation data that correlated reasonably well with measured electrical activation sequence in both animals and man. Analysis of wall motion may not predict activation sequence when muscle is damaged or excessive translational movement of the heart occurs. Body surface mapping of electrical potentials has the capability to accurately but noninvasively register an electrical activation image of the heart that circumvents the problems of imaging contraction sequence. In the future, body surface potential mapping should be more widely used clinically and experimentally.

Detection of electrocardiographically imperceptible ventricular pre-excitation by phase imaging

The sequence of ventricular contraction was studied by radionuclide phase imaging in 25 patients with Wolff-Parkinson-White syndrome. The studies were performed when no signs of precontraction were present in the electrocardiogram; in these cases pre-excitation was either intermittent or suppressable by injection of ajmaline. In 11 of the 16 patients with free wall accessory pathways, precontraction could be detected in spite of electrocardiographically absent pre-excitation. Discrete precontraction was seen also in 2 of the 9 patients with paraseptal accessory pathways. We conclude that antegrade conduction through the accessory pathway does not need to be completely blocked if signs of pre-excitation are absent on the electrocardiogram, and that phase imaging is, at least in some patients (especially those with free wall accessory pathways), a more sensitive technique for detection of pre-excitation (precontraction) than the electrocardiogram.

Nuclear tomographic phase analysis: localization of accessory conduction pathway in patients with Wolff-Parkinson-White syndrome

The purpose of this study was to evaluate the usefulness of tomographic phase analysis in detecting the site of the accessory conduction pathway (ACP) in patients with Wolff-Parkinson-White (WPW) syndrome. Gated emission computed tomography and planar gated blood pool scintigraphy were performed in 20 patients with WPW syndrome, 14 with delta waves and six without delta waves (two intermittent types and four concealed types). The abnormal initial contractions in both planar and tomographic phase images were compared with the sites of ACPs confirmed by epicardial mapping and surgery. The atrioventricular ring was divided into eight segments on each side, and the identification of the initial phase in the segment in which the ACP was located, or that adjacent to it, was considered to be the correct diagnosis. In planar phase analysis, the abnormal initial phase was identified correctly in 8 of 14 patients (57%), whereas in tomographic phase analysis, the site of the ACP was detected in 12 of 14 patients (86%). Tomographic phase analysis can be a helpful adjunctive method in patients with WPW syndrome.