Background-Transmyocardial laser revascularization (TMR) has been shown to improve refractory angina not amenable to conventional coronary interventions. However, the mechanism of action remains controversial, because improved myocardial perfusion has not been consistently demonstrated. We hypothesized that TMR relieves angina by causing myocardial sympathetic denervation. Methods and Results-PET imaging of resting and stress myocardial perfusion with [13 N]ammonia (NH 3 ) and of sympathetic innervation with [11 C]hydroxyephedrine (HED) was performed before and after TMR in 8 patients with class IV angina ineligible for CABG or PTCA. A mean of 50Ϯ11 channels were created in the left ventricle (LV) with a holmium:YAG laser. A semiautomated program was used to determine NH 3 uptake and HED retention in the LV. Perfusion and innervation defects were defined as the percentage of LV with tracer uptake or retention Ͼ2 SD below normal mean values. All patients experienced improvement in their angina by 2.4Ϯ0.5 angina classes after surgery, Pϭ0.008. Sympathetic innervation defects exceeded resting perfusion defects in all patients before TMR (34.6Ϯ27.3% for HED versus 9.4Ϯ10.8% for NH 3 , Pϭ0.008). TMR did not significantly affect resting or stress myocardial perfusion but increased the extent of sympathetic denervation in 6 of 8 patients by 27.5Ϯ15.9%, Pϭ0.03. In the remaining 2 patients, both sympathetic denervation and stress perfusion defects decreased after surgery. Conclusions-TMR causes decreased myocardial HED uptake in most patients without significant change in resting or stress myocardial perfusion, suggesting that the improvement in angina may be at least in part due to sympathetic denervation. (Circulation. 1999;100:135-140.)

Intermediate Septal Bypass Tracts. Introduction: Intermediate seplal (TS) AV bypass tracts, located uli>n}> the tricuspid annulus hetween the His hund(e and coronary sinus os. lie in close proximity to the AV node. Surgical or catheter ahlation of IS hypass tracts incurs increased risk for development of complete heart hlwk. We report additional unusual features of some IS hypass tracts that distinguish them from typical hypass tracts in other anatomic regions.Methods and Results: We analyzed a consecutive series of 150 patients with a history of Wolff-Parkinson-White syndrome and supraventricular tachycardia who underwent ahiation of hypass tracts. We studied the incidence and characteristics of AV conduction of IS hypass tracts compared with hypass tracts in other locations. Of the 150 patients in the stndy. 21 had an IS hypass tract (all had anterograde \\ conduction). Ten (4KVr) of these 21 IS hypass tracts demonstrated anterograde decremental properties with atrial pacing versus 3 (2%) of 129 non-IS hypass tracts (P < 0.001). During ahlation, a change in delta wave morphology before total loss of conduction in the IS hypass tract also iK'curred in 3 {\49c) of 21 IS hypass tracts versus 0 of I2M non-lS hypass tracts (P = OJMMMl. During ahlation. a change in P wave to delta wave interval occurred in 4 (I9f^) of 21 IS bypass tracts versus 0 of 129 non-IS hypass tracts (P < O.4HK)I). One IS patient exhihited retrograde Wenckehach hlock in the hypass tract, and two IS patients showed loss of retrograde hypass tract conduction after ahlation attempts that first changed the delta wave morphology. No non-IS patient had these features (P < O.OOOI for each comparison).Conclusion: Some IS bypass tracts have unusual properties that distinguish them from hypass tracts in other locations, perhaps due to the presence of multiple ventricular insertions of the bypass tract. It is possible that some cases represent true "nodoventricular" pathways. (J Cardiovasc Electrophysiol. VoL II. pp. 7M)-7S5. July 20()0) Wolff-Parkinson-White syndrome, catheter ablation, preexcitation variantsThis manuscript was prtx'cssed by a guest editor.

Catheter mapping and radiofrequency ablation of postinfarct sustained ventricular tachycardia (VT) remain one of the greatest challenges for the electrophysiologist. Although there were no major breakthroughs during the past year, several refinements and clarifications of existing mapping criteria were published. In addition, initial reports appeared describing new mapping systems and ablation technologies that may significantly impact the way ablation studies are performed as well as the way in which they affect success rates. Uncertainties remain as to how effective catheter ablation will be as a longterm cure for this type of VT. For the foreseeable future, catheter ablation in postinfarct VT will remain adjunctive rather than primary therapy.

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