Diminished cardiac fibrosis in heart failure is associated with altered ventricular arrhythmia phenotype.
OBJECTIVE
We sought to define the role of interstitial fibrosis in the proarrhythmic phenotype of failing ventricular myocardium.


BACKGROUND
Multiple cellular events that occur during pathological remodeling of the failing ventricle are implicated in the genesis of ventricular tachycardia (VT), including interstitial fibrosis. Recent studies suggest that ventricular fibrosis is reversible, and current anti-remodeling therapies attenuate ventricular fibrosis. However, the role of interstitial fibrosis in the proarrhythmic phenotype of failing ventricular myocardium is currently not well defined.


METHODS
Class II histone deacetylases (HDACs) have been implicated in promoting collagen biosynthesis. As these enzymes are inhibited by protein kinase D1 (PKD1), we studied mice with cardiomyocyte-specific transgenic over-expression of a constitutively active mutant of PKD1 (caPKD). caPKD mice were compared with animals in which cardiomyopathy was induced by severe thoracic aortic banding (sTAB). Hearts were analyzed by echocardiographic and electrocardiographic means. Interstitial fibrosis was assessed by histology and quantified biochemically. Ventricular arrhythmias were induced by closed-chest, intracardiac pacing.


RESULTS
Similar degrees of hypertrophic growth, systolic dysfunction and mortality were observed in the two models. In sTAB mice, robust ventricular fibrosis was readily detected, but myocardial collagen content was significantly reduced in caPKD mice. As expected, VT was readily inducible by programmed stimulation in sTAB mice and VT was less inducible in caPKD mice. Surprisingly, episodes of VT manifested longer cycle lengths and longer duration in caPKD mice.


CONCLUSIONS
Attenuated ventricular fibrosis is associated with reduced VT inducibility, increased VT duration, and significantly longer arrhythmia cycle length.
Department of Internal Medicine (Cardiology), University of Texas Southwestern Medical Center, Dallas, Texas 75390-8573, USA.
Jorge
J
Massare
Jeff M
JM
Berry
Xiang
X
Luo
Farhana
F
Rob
Janet L
JL
Johnstone
John M
JM
Shelton
Rhonda
R
Bassel-Duby
Joseph A
JA
Hill
R Haris
RH
Naseem
D000200:Action Potentials; D000818:Animals; D002311:Cardiomyopathy, Dilated / Q000150:complications* / Q000201:enzymology / Q000473:pathology / Q000503:physiopathology; D004195:Disease Models, Animal; D022062:Electrophysiologic Techniques, Cardiac; D005355:Fibrosis; D005838:Genotype; D006333:Heart Failure / Q000201:enzymology / Q000209:etiology* / Q000473:pathology / Q000503:physiopathology; D008297:Male; D051379:Mice; D008810:Mice, Inbred C57BL; D008822:Mice, Transgenic; D009154:Mutation; D009206:Myocardium / Q000201:enzymology / Q000473:pathology*; D010641:Phenotype; D011493:Protein Kinase C / Q000235:genetics / Q000378:metabolism; D017180:Tachycardia, Ventricular / Q000201:enzymology / Q000209:etiology* / Q000235:genetics / Q000473:pathology / Q000503:physiopathology / Q000517:prevention & control; D015854:Up-Regulation; D020257:Ventricular Remodeling
C089212:protein kinase D; D011493:Protein Kinase C