DEMONSTRATION OF THE MECHANICAL EQUIVALENT OF ELECTRICAL PREEXCITATION

The mechanical consequence of electrical pre-excitation is earlier contraction. A variety of techniques have been previously investigated to demonstrate this including roentgenkymography and echocardiography. We used phase analysis of the gated cardiac radionuelide ventriculogram for t h s purpose. Eight patients with manifest pre-excitation and three with “concealed” accessory pathways were studied. Standard electrocardiograms were available in all and endocardia1 electrophysiological mapping was performed in seven of the eleven patients. Oesophageal pacing was atteniptcd in seven of the patients. The patients ranged in age from 13 to 62 years. Three patients had no evidence of pre-excitation on the surface ECG but an accessory pathway was found to be the retrograde limb of the re-entrant circuit during electrophysiologically induced tachycardias in each. Four patients had a typc A ECG pattern (Ueda et id.). one a type B and three a type C on the surface ECG during sinus rhythm. The phase pattern during sinus rhythm was no different from the normal pattern (previously determined in ten normal volunteers) in two of the eight patients with manifest pre-excitation and type C ECG pattern. Ncither of these patients had electrophysiological studies. The phase pattern was different from normal in the remaining six of the eight patients with manifest preexcitation. Ectopic segments that emptied early were seen in the left ventricle in five patients and in the right ventricle in one patient. Electrophysiologic mapping was available in four of these six patients and s h o w d concordant results. All three of the patients with “concealed” accessory pathways had abnormal phase patterns. Two had ectopic islands of early emptying in the left ventricle and one in the right ventricle despite the absence of delta waves on the ECG. Electrophysiological mapping in all three confirmed the presence of an accessory pathway capable of retrograde conduction only in two and bidirectional conduction in one patient. The site of the pathway corresponded to the phase maps in all three patients. With transoesophageal atrial pacing, two patients had larger delta waves. One showed an enlargement in the leftsided focus of early emptying on the phase image, the other patient, whose phase map was normal during sinus rhythm, showed n o change from normal. One patient had a normalisation of the QRS with pacing and a concomitant diminution of the right-sided focus of early emptying in the phase image. Four patients developed supraventricular tachycardia with pacing and the abnormal phase maps during sinus rhythm were converted to normal ones. Conclusion: Phase analysis can clearly demonstrate the mechanical equivalent of electrical pre-excitation in most patients with manifest pre-excitation. “Concealed” accessory pathways are visible on phase images even if they are not evident on surface ECG. The presence of a normal phase map does not excludc pre-excitation. This technique rcquires further study, but appears useful as a screening procedure for latcralising the site of pre-excitation.