Left bundle branch block induces ventricular remodelling and functional septal hypoperfusion.
OBJECTIVE
Left ventricular (LV) dilatation, hypertrophy, and septal perfusion defects are frequently observed in patients with left bundle branch block (LBBB). We investigated whether isolated LBBB causes these abnormalities.


RESULTS
In eight dogs, LBBB was induced by radio frequency ablation. Two-dimensional echocardiography showed that 16 weeks of LBBB decreased LV ejection fraction (by 23+/-14%) and increased LV cavity volume (by 25+/-19%) and wall mass (by 17+/-16%). The LV septal-to-lateral wall mass ratio decreased by 6+/-9%, indicating asymmetric hypertrophy. After onset of LBBB, myocardial blood flow (MBF, fluorescent microspheres) and systolic circumferential shortening [CS(sys), magnetic resonance (MR) tagging] decreased in the septum to 83+/-16% and -11+/-20% of baseline, respectively, and increased in LV lateral wall to 118+/-12% and 180+/-90% of baseline, respectively. MBF and CS(sys) values did not change over 16 weeks of LBBB. Changes in external mechanical work paralleled those in CS(sys). Glycogen content was not significantly different between septum and LV lateral wall of LBBB hearts (16 weeks) and control samples, indicating absence of hibernation.


CONCLUSIONS
The asynchronous ventricular activation during LBBB leads to redistribution of circumferential shortening and myocardial blood flow and, in the long run, LV remodelling. Septal hypoperfusion during LBBB appears to be primarily determined by reduced septal workload.
Vernooy
Kevin
K
Department of Physiology, Cardiovascular Research Institute Maastricht, PO Box 616, 6200 MD Maastricht, The Netherlands. k.vernooy@fys.unimaas.nl
Verbeek
Xander A A M
XA
Peschar
Maaike
M
Crijns
Harry J G M
HJ
Arts
Theo
T
Cornelussen
Richard N M
RN
Prinzen
Frits W
FW
D000818:Animals; D001145:Arrhythmias, Cardiac / Q000209:etiology / Q000503:physiopathology; D002037:Bundle-Branch Block / Q000150:complications* / Q000473:pathology / Q000503:physiopathology; D002311:Cardiomyopathy, Dilated / Q000473:pathology / Q000503:physiopathology; D003326:Coronary Circulation / Q000502:physiology; D004285:Dogs; D005260:Female; D018810:Magnetic Resonance Angiography / Q000379:methods; D008297:Male; D013318:Stroke Volume / Q000502:physiology; D013599:Systole / Q000502:physiology; D020257:Ventricular Remodeling / Q000502:physiology*