Effect of left ventricular dyssynchrony on plasma B-type natriuretic peptide levels in patients with long-term right ventricular apical pacing

Left ventricular systolic dysfunction induced by ventricular ectopy: a novel model for premature ventricular contraction-induced cardiomyopathy

BACKGROUND

Premature ventricular contractions (PVCs) commonly coexist with cardiomyopathy. Recently, PVCs have been identified as a possible cause of cardiomyopathy. We developed a PVC-induced cardiomyopathy animal model using a novel premature pacing algorithm to assess timeframe and reversibility of this cardiomyopathy and examine the associated histopathologic abnormalities.

METHODS AND RESULTS

Thirteen mongrel dogs were implanted with a specially programmed pacemaker capable of simulating ventricular extrasystoles. Animals were randomly assigned to either 12 weeks of bigeminal PVCs (n = 7) or no PVCs (control, n = 6). Continuous 24-hour Holter monitoring corroborated ventricular bigeminy in the PVC group (PVC, 49.8% versus control, < 0.01%; P<0.0001). After 12 weeks, only the PVC group had cardiomyopathy, with a significant reduction in left ventricular ejection fraction (PVC, 39.7 ± 5.4% versus control, 60.7 ± 3.8%; P < 0.0001) and an increase in left ventricular end-systolic dimension (PVC, 33.3 ± 3.5 mm versus control, 23.7 ± 3.6 mm; P < 0.001). Ventricular effective refractory period showed a trend to prolong in the PVC group. PVC-induced cardiomyopathy was resolved within 2 to 4 weeks after discontinuation of PVCs. No inflammation, fibrosis, or changes in apoptosis and mitochondrial oxidative phosphorylation were observed with PVC-induced cardiomyopathy.

CONCLUSIONS

This novel PVC animal model demonstrates that frequent PVCs alone can induce a reversible form of cardiomyopathy in otherwise structurally normal hearts. PVC-induced cardiomyopathy lacks gross histopathologic and mitochondrial abnormalities seen in other canine models of cardiomyopathy.

Interpretation and use of natriuretic peptides in non-congestive heart failure settings

Natriuretic peptides (NPs) have been found to be useful markers in differentiating acute dyspneic patients presenting to the emergency department (ED) and emerged as potent prognostic markers for patients with congestive heart failure (CHF). The best-established and widely used clinical application of BNP and NT-proBNP testing is for the emergent diagnosis of CHF in patients presenting with acute dyspnea. Nevertheless, elevated NPs levels can be found in many circumstances involving left ventricular (LV) dysfunction or hypertrophy; right ventricular (RV) dysfunction secondary to pulmonary diseases; cardiac inflammatory or infectious diseases; endocrinology diseases and high output status without decreased LV ejection fraction. Even in the absence of significant clinical evidence of volume overload or LV dysfunction, markedly elevated NP levels can be found in patients with multiple comorbidities with a certain degree of prognostic value. Potential clinical applications of NPs are expanded accompanied by emerging reports regarding screening the presence of secondary cardiac dysfunction; monitoring the therapeutic responses, risk stratifications and providing prognostic values in many settings. Clinicians need to have expanded knowledge regarding the interpretation of elevated NPs levels and potential clinical applications of NPs. Clinicians should recognize that currently the only reasonable application for routine practice is limited to differentiation of acute dyspnea, rule-out-diagnostic-tests, monitoring of therapeutic responses and prognosis of acute or decompensated CHF. The rationales as well the potential applications of NPs in these settings are discussed in this review article.

Tissue doppler changes in pediatric complete heart block patients who are chronically paced

INTRODUCTION

Pediatric patients with complete heart block (CHB) often require pacemaker therapy. Adult studies have shown chronic right ventricular pacemaker therapy may be associated with decreased echocardiographic parameters and increased brain natriuretic peptide (BNP) values. The goal of this study was to determine if there are echocardiographic or BNP changes in a pediatric population that is chronically paced.

METHODS

Patients were recruited if they had CHB and had a pacemaker. Patients were excluded if they had congenital structural heart disease. Standard two-dimensional echocardiograms, including tissue Doppler imaging (TDI), were performed. BNP values were obtained. Nonparametric Spearman's rank correlation was used for analysis. Rho < or = 0.05 was considered significant.

RESULTS

Eighteen patients (16.4 +/- 7.3 years) with CHB were studied. Age at implant was 8.6 +/- 6.6 years and length of pacing was 7.8 +/- 6.6 years. Pacing mode was VDD, DDD, DDDR, or VVIR. All patients were ventricularly paced >95% of the time. Ejection fraction was 58.5 +/- 7.5%. All BNP values were <40 pg/mL. There was no correlation between ejection fraction or BNP level with the length of pacing years. Pacing years significantly correlated with mitral and tricuspid E/A ratios (rho =-0.56, -0.56, respectively). Pacing years also correlated with right ventricular and interventricular TDI a wave (rho = 0.61 and 0.68, respectively). Furthermore, pacing years correlated with right ventricular TDI e/a ratio (rho =-0.58).

CONCLUSIONS

Ejection fraction and BNP levels were not sensitive parameters in evaluating pediatric patients who are chronically paced. Subtle diastolic changes, especially of the right ventricle, were detected by TDI.

Asymmetrical myocardial expression of natriuretic peptides in pacing-induced heart failure

High-frequency pacing of the left ventricle (LV) free wall causes a dyssynchronous pattern of contraction that leads to progressive heart failure (HF) with pronounced differences in regional contractility. Aim of this study was to evaluate possible changes in brain natriuretic peptide (BNP) and C-type natriuretic peptide (CNP) mRNA expression in the anterior/anterior lateral region (pacing site, PS) as compared to the infero-septal region (opposite site, OS) and to explore possible association between the contractiling pattern and biomarker expression. Cardiac tissue was collected from minipigs with pacing-induced HF (n=8) and without (control, n=6). The samples were selectively harvested from the anterior left ventricular (LV) wall, PS, and from an area remote to the pacing-site, OS. BNP and CNP mRNA expression was evaluated by semi-quantitative polymerase chain reaction (PCR). A significant difference in BNP expression was found in the PS between HF animals and controls (BNP/GAPDH: 0.65+/-0.11 vs. 0.35+/-0.04, p=0.02), but not in the OS (BNP/GAPDH: 0.36+/-0.05, ns vs. controls). CNP expression was not different compared to controls, although higher levels were observed in the PS and in the OS with respect to the controls (CNP/GAPDH: controls 0.089+/-0.036, PS 0.289+/-0.23, OS 0.54+/-0.16). This finding was in tune with an increase of CNP tissue concentration (controls: 0.69+/-0.13; PS=1.56+/-0.19; OS=1.70+/-0.42 pg/mg protein; p=0.039 controls vs. OS). Higher BNP mRNA expression in the PS is consistent with a reduction in contractile function in this region, while higher CNP mRNA expression in the OS suggests the presence of concomitant endothelial dysfunction in the remote region.