Genotypic and phenotypic predictors of complete heart block and recovery of conduction after surgical repair of congenital heart disease.

BACKGROUND: Complete heart block (CHB) is a major complication that occurs after congenital heart surgery. We hypothesized that genetic and clinical factors are associated with the development of postoperative CHB and recovery of atrioventricular (AV) conduction. OBJECTIVE: The purpose of this study was to identify predictors of CHB and recovery after congenital heart surgery. METHODS: Patients undergoing congenital heart surgery at our institution from September 2007 through June 2015 were prospectively enrolled in a parent study of postoperative arrhythmias. Patients with onset of CHB within 48 hours postoperatively were included in the study. Daily rhythm assessment was performed until demonstration of 1:1 conduction or pacemaker implantation. RESULTS: Of 1199 subjects enrolled, 56 (4.7%) developed postoperative CHB. In multivariate analysis, preoperative digoxin exposure (odds ratio [OR] 2.4, 95% confidence interval [CI] 1.3-4.4), aortic cross-clamp time (OR 1.08, 95% CI 1.04-1.11), ventricular septal defect closure (OR 2.2, 95% CI 1.2-4.1), and a common polymorphism in the gene encoding connexin-40 (GJA5 rs10465885 TT genotype; OR 2.1, 95% CI 1.2-3.8) were independently associated with postoperative CHB. Junctional acceleration (JA) (OR 4.0, 95% CI 1.1-15.1) and intermittent conduction noted during complete AV block (OR 9.1, 95% CI 1.0-80) were independently associated with 1:1 AV conduction recovery. Use of a multivariate model including both JA and intermittent conduction demonstrated good discrimination with a positive predictive value of 86% (95% CI 67%-96%) in predicting 1:1 conduction recovery. CONCLUSION: Preoperative factors, including a missense polymorphism in GJA5, are independently associated with increased risk for CHB. JA and intermittent conduction may prove useful in predicting recovery of AV conduction among patients with CHB after congenital heart surgery.

A common angiotensin-converting enzyme polymorphism and preoperative angiotensin-converting enzyme inhibition modify risk of tachyarrhythmias after congenital heart surgery.

BACKGROUND: The angiotensin-converting enzyme insertion/deletion (ACE I/D) polymorphism is described in association with numerous phenotypes, including arrhythmias, and may provide predictive value among pediatric patients undergoing congenital heart surgery. OBJECTIVE: The purpose of this study was to examine the role of a common polymorphism on postoperative tachyarrhythmias in a large cohort of pediatric patients undergoing congenital heart surgery with cardiopulmonary bypass (CPB). METHODS: Subjects undergoing congenital heart surgery with CPB at our institution were consecutively enrolled from September 2007 to December 2012. In addition to DNA, perioperative clinical data were obtained from subjects. RESULTS: Postoperative tachyarrhythmias were documented in 45% of 886 enrollees and were associated with prolonged mechanical ventilation (P <.001) and intensive care unit length of stay (P <.001). ACE I/D was in Hardy-Weinberg equilibrium (19% I/I, 49% I/D, 32% D/D). I/D or D/D genotypes were independently associated with a 60% increase in odds of new tachyarrhythmia (odds ratio [OR] 1.6, 95% confidence interval [CI] 1.1-2.3, P = .02). Preoperative ACE inhibitor administration was independently associated with a 47% reduction in odds of postoperative tachyarrhythmia in the entire cohort (OR 0.53, 95% CI 0.32-0.88, P = .01), driven by a 5-fold reduction in tachyarrhythmias among I/I genotype patients (OR 0.19, 95% CI 0.04-0.88, P = .02). CONCLUSION: The risk of tachyarrhythmias after congenital heart surgery is independently affected by the ACE I/D polymorphism. Preoperative ACE inhibition is associated with a lower risk of postoperative tachyarrhythmias, an antiarrhythmic effect that appears genotype dependent. An understanding of genotype variation may play an important role in the perioperative management of congenital heart surgery.

Membrane-type-1 matrix metalloproteinase transcription and translation in myocardial fibroblasts from patients with normal left ventricular function and from patients with cardiomyopathy.

Past studies have identified that a unique type of matrix metalloproteinase, the membrane-type-1 MMP (MT1-MMP), is increased within the left ventricle (LV) of patients with dilated cardiomyopathy (DCM). However, the cellular and molecular basis for this induction of MT1-MMP with DCM is unknown. LV myocardial biopsies from nonfailing, reference normal patients (defined as LV ejection fraction >50%, elective coronary bypass surgery, no perfusion defect at biopsy site, n = 6) and DCM patients (LV ejection fraction <20%, at transplant, n = 5) were used to establish fibroblast cultures (FIBROS). Confluent LV FIBROS from culture passages 2-5 were measured with respect to MT1-MMP mRNA and protein levels and the distribution of the MT1-MMP mRNA pool in ribosomal fractions. Total MT1-MMP mRNA within DCM FIBROS increased by over 140%, and MT1-MMP protein increased by over 190% from reference normal FIBROS (both P < 0.05). MT1-MMP mRNA in monosome fractions decreased by over twofold in DCM FIBROS compared with reference normal (P < 0.05) and remained lower in polyribosomal fractions (i.e., 15.7 +/- 5.2 vs. 1.4 +/- 0.6% in polysomal fraction 6, P < 0.05). These differences in DCM MT1-MMP FIBROS transcription and translation persisted throughout passages 2-5. The unique findings from this study demonstrated that elevated steady-state MT1-MMP mRNA and protein levels occurred in DCM FIBROS despite a decline in translational deficiency. These phenotypic changes in DCM fibroblasts may provide the basis for developing cell specific pharmacological targets for control of MT1-MMP expression.

Alterations in cultured myocardial fibroblast function following the development of left ventricular failure.

A structural event in the progression of left ventricular (LV) failure is myocardial extracellular matrix (ECM) remodeling. The myocardial fibroblast is a major cell type influencing the ECM, but whether and to what degree specific phenotypic differences in myocardial fibroblasts can be demonstrated to occur in culture with the development of LV failure remains unclear. Adult pigs (25 kg) were used for control myocardial fibroblast preparations (N=5) or following pacing-induced LV failure (N=5; 240 bpm, 3 weeks). LV remodeling occurred with pacing as evidenced by increased LV end diastolic volume (132+/-11 vs. 60+/-4 mL for control; P<0.05). Functional parameters including migration, adhesion, collagen and matrix metalloproteinase release were assessed in fibroblast cultures from passages 1-4. The following findings were consistent with each passage and the results were analyzed with control values set to 100%. Migration of LV failure fibroblasts increased by over 170% (P<0.05). Adhesion to collagen I, laminin and fibronectin was increased by over 160% in LV failure fibroblasts (P<0.05). beta(1) integrin density decreased by 50% in LV failure fibroblasts (P<0.05). Fibrillar collagen release increased by over 130% and matrix metalloproteinase-2 increased by 140% in LV failure fibroblasts (P<0.05). The unique findings of this study are two-fold. First, after a pathological stimulus in-vivo, adult myocardial fibroblasts maintain a consistent phenotype through early passages in-vivo. Second, a differential release of, and response to ECM components occurred in LV failure fibroblasts. Thus, a phenotypic transformation of the myocardial fibroblast occurs with the development of LV failure, which in turn may contribute to matrix remodeling and presents as a potential cellular therapeutic target.

Altered fibroblast function following myocardial infarction.

Adequate wound healing and scar formation is an essential response to myocardial infarction (MI), and fibroblasts are primary cellular components regulating the process. How fibroblast functions are altered post-MI and to what extent these abnormalities persist in vitro is not well understood. Accordingly, we isolated myocardial fibroblasts from MI and non-MI (remote) regions at 7 days post-MI (n=35) and from the free wall and septum of unoperated control C57BL/6 mice (n=14). Proliferation was increased 182+/-28% in MI, but not in remote, fibroblasts compared with unoperated controls (P=0.01). Migration decreased 61+/-8%, adhesion to laminin decreased 79+/-8%, adhesion to collagen IV increased 196+/-27%, and collagen synthesis increased 169+/-24% in fibroblasts isolated from the MI region (all P<0.05). Migration, adhesion, and collagen synthesis changes were similar in remote fibroblasts, and the phenotypic differences were maintained through passage four. Transforming growth factor beta1 (TGFbeta1) is a bioactive molecule that has been shown to affect fibroblast function. Stimulation of unoperated control fibroblasts with 10 ng/ml TGFbeta(1) increased proliferation 137+/-7% (P=0.03 vs. unstimulated), increased adhesion to collagen IV 149+/-6% (P<0.01), and increased collagen I levels 187+/-10% (P=0.01). TGFbeta1 may, therefore, explain some of the changes in post-MI fibroblast phenotype. These data demonstrate for the first time region specific alterations in post-MI fibroblast biology that are maintained in vitro. Additionally, our model provides a novel in vitro template for examining the cellular mechanisms of wound healing and scar formation post-MI.