Left bundle branch block causes relative but not absolute septal underperfusion during exercise.
OBJECTIVE
Left bundle branch block (LBBB) often causes septal perfusion defects in radionuclide myocardial perfusion imaging using exercise (Ex) but rarely using vasodilator stress. We studied whether this is due to an underlying structural disease inherent to spontaneous LBBB or whether it is also found in temporary LBBB induced by right ventricular pacing (PM) indicating a functional rather than a structural alteration.


RESULTS
Regional myocardial blood flow (MBF) at rest and at Ex was measured with 15O-H2O and PET in 10 age-matched healthy volunteers (controls), 10 LBBB patients and 10 PM patients with right ventricular pacing off and on (PM off and PM on). Although at Ex septal MBF tended to be higher in LBBB than in controls (3.04 +/- 1.18 vs. 2.27 +/- 0.72 mL/min/g; P = ns), the ratio septal/lateral MBF was 19% lower in LBBB than in controls (P < 0.05). Similarly, switching PM on at Ex decreased the ratio septal/lateral MBF by 17% (P < 0.005).


CONCLUSIONS
The apparent septal perfusion defect in LBBB is mainly due to a relative lateral hyperperfusion rather than to an absolute septal flow decrease. This pattern seems to be reversibly inducible by right ventricular pacing, suggesting a functional rather than a structural alteration.
Koepfli
Pascal
P
Cardiac Imaging, University Hospital, NUK C42, Raemistr. 100, CH-8091 Zurich, Switzerland.
Wyss
Christophe A
CA
Gaemperli
Oliver
O
Siegrist
Patrick T
PT
Klainguti
Michael
M
Schepis
Tiziano
T
Namdar
Mehdi
M
Bechir
Markus
M
Hoefflinghaus
Tobias
T
Duru
Firat
F
Kaufmann
Philipp A
PA
D000368:Aged; D002037:Bundle-Branch Block / Q000000981:diagnostic imaging / Q000503:physiopathology* / Q000628:therapy; D002304:Cardiac Pacing, Artificial; D009202:Cardiomyopathies / Q000209:etiology* / Q000503:physiopathology; D016022:Case-Control Studies; D003326:Coronary Circulation / Q000502:physiology*; D015444:Exercise / Q000502:physiology*; D005260:Female; D006346:Heart Septum / Q000503:physiopathology*; D006801:Humans; D008297:Male; D008875:Middle Aged; D049268:Positron-Emission Tomography