[Pacemaker implantation in children: is this a therapy or a pathogenetic mechanism for ventricular dysfunction?]

Ventricular pacing, typically initiated from a right ventricular apical electrode, inherently causes abnormal biventricular activation, decreases left ventricular function, and may cause histopathological changes. Data regarding cardiac resynchronization therapy in pediatric patients are limited. Some authors evaluated the potential of improving paced left ventricular function by a septal electrode implant site. For this reason the role of pacing is not clear in children. In isolated congenital atrioventricular block, cardiac pacing represents a satisfactory treatment. However, recent evidence has demonstrated that a subset of patients with isolated congenital complete atrioventricular block develops dilated cardiomyopathy. Patients with congenital heart diseases after surgery represent a unique and expanding population. Some will require pacemaker or implantable defibrillator therapy. They pose technical and management challenges not encountered in other groups receiving pacing, and the complication and reintervention rates specific to this population are not well defined. Moreover, the small patient size, structural cardiac abnormalities, and growth may complicate pediatric pacemaker management. Better knowledge of risk factors for lead failure in these patients may help improve future outcomes. In this review we analyzed many of these problems.

Cell transplantation: Differential effects of myoblasts and mesenchymal stem cells

BACKGROUND

Cellular transplantation has emerged as a novel therapeutic option for treatment of ventricular dysfunction. Both skeletal myoblasts (SM) and mesenchymal stem cells (MSC) have been proposed as ideal cell for this aim. The aim of this study is to compare the efficacy of these cells in improving ventricular function and to evaluate the different histological findings in a rat model of severe post-infarct ventricular dysfunction.

METHODS

Myocardial infarction was induced in Wistar rats by left coronary occlusion. Animals with resulting ejection fraction (EF) lower than 40% were included. Heterologous SM were obtained by lower limb muscle biopsy and MSC by bone marrow aspiration. Nine days after infarction, rats received intramyocardial injection of SM (n=8), MSC (n=8) or culture medium, as control (n=11). Echocardiographic evaluation was performed at baseline and after 1 month. Histological evaluation was performed after HE and Gomori's trichrome staining and immunostainig against desmin, fast myosin and factor VIII.

RESULTS

There was no difference in baseline EF and left ventricular end diastolic (LVEDV) and systolic volume (LVESV) between all groups. After 1 month a decrease was observed in the EF in the control group (27.0+/-7.10% to 21.46+/-5.96%, p=0.005) while the EF markedly improved in SM group (22.66+/-7.29% to 29.40+/-7.01%, p=0.04) and remained unchanged in the MSC group (23.88+/-8.44% to 23.63+/-10.28%, p=0.94). Histopathology identified new muscular fibers in the group that received SM and new vessels and endothelial cells in the MSC.

CONCLUSION

Skeletal myoblasts transplantation resulted in myogenesis and improvement of ventricular function. In contrast, treatment with mesenchymal stem cells resulted in neoangiogenesis and no functional effect.

Myocardial infarction in isolated ventricular non-compaction: Contrast echo and MRI

We describe the case of an occasional discovery of isolated ventricular non-compaction in an adult recovered for an acute myocardial infarction, in which only the echocardiogram revealed an isolated ventricular non-compaction, confirmed by MRI: an unusual association between coronary artery disease and isolated ventricular non-compaction.

Electrophysiological mechanisms of ventricular arrhythmias in relation to Andersen-Tawil syndrome under conditions of reduced IK1: a simulation study

Patients with Andersen-Tawil syndrome (ATS) mostly have mutations on the KCNJ2 gene, producing loss of function or dominant-negative suppression of the inward rectifier K(+) channel Kir2.1. However, clinical manifestations of ATS including dysmorphic features, periodic paralysis (hypo-, hyper-, or normokalemic), long QT, and ventricular arrhythmias (VAs) are considerably variable. Using a modified dynamic Luo-Rudy simulation model of cardiac ventricular myocytes, we attempted to elucidate mechanisms of VA in ATS by analyzing effects of the inward rectifier K(+) channel current (I(K1)) on the action potential (AP). During pacing at 1.0 Hz with extracellular K(+) concentration ([K(+)](o)) at 4.5 mM, a stepwise 10% reduction of Kir2.1 channel conductance progressively prolonged the terminal repolarization phase of the AP along with gradual depolarization of the resting membrane potential (RMP). At 90% reduction, early afterdepolarizations (EADs) became inducible and RMP was depolarized to -52.0 mV (control: -89.8 mV), followed by emergence of spontaneous APs. Both EADs and spontaneous APs were facilitated by a decrease in [K(+)](o) and suppressed by an increase in [K(+)](o). Simulated beta-adrenergic stimulation enhanced delayed afterdepolarizations (DADs) and could also facilitate EADs as well as spontaneous APs in the setting of low [K(+)](o) and reduced Kir2.1 channel conductance. In conclusion, the spectrum of VAs in ATS may include 1) triggered activity mediated by EADs and/or DADs and 2) abnormal automaticity manifested as spontaneous APs. These VAs can be aggravated by a decrease in [K(+)](o) and beta-adrenergic stimulation and may potentially induce torsade de pointes and cause sudden death. In patients with ATS, the hypokalemic form of periodic paralysis should have the highest propensity to VAs, especially during physical activity.

[Echocardiographic criteria for the definition of ventricular dysfunction severity in aortic banded rats]

OBJECTIVE

The purpose of this study was to identify echocardiographic parameters that allow distinguishing different levels of cardiac dysfunction in aortic banded rats.

METHODS

Wistar male rats (90-100 g) were subjected to aortic banding (n=23) or a sham operation (n=12). The following echocardiographic parameters were evaluated and used to group rats into groups with similar characteristics using cluster analysis: absolute values and after normalization to body weight of left ventricular end-diastolic diameter (LVDD) and left atrial systolic diameter; left ventricular end-systolic diameter (LVSD); LV weight to body weight ratio (LVW/BW); three indexes of left ventricular shortening (endocardial fractional shortening, EFS; midwall FS, MFS; and posterior wall shortening velocity, (PWSV).

RESULTS

The cluster analysis could group aortic banded rats into two groups: mild (n=13) and severe (n=9) stage of heart failure. There was no overlapping among the values of the 95% confidence interval of the following parameters between the two groups: LVDD, LVSD, EFS, MFS, LVW/BW, and PWSV.

CONCLUSION

It is feasible to distinguish two groups of aortic banded rats according to the level of cardiac dysfunction using those echocardiographic parameters. This allows to perform longitudinal studies in homogeneous groups of rats with aortic banding and cardiac dysfunction.

Ambient particulate air pollution and cardiac arrhythmia in a panel of older adults in Steubenville, Ohio

OBJECTIVES

Ambient particulate air pollution has been associated with increased risk of cardiovascular morbidity and mortality. Pathways by which particles may act involve autonomic nervous system dysfunction or inflammation, which can affect cardiac rate and rhythm. The importance of these pathways may vary by particle component or source. In an eastern US location with significant regional pollution, the authors examined the association of air pollution and odds of cardiac arrhythmia in older adults.

METHODS

Thirty two non-smoking older adults were evaluated on a weekly basis for 24 weeks during the summer and autumn of 2000 with a standardised 30 minute protocol that included continuous electrocardiogram measurements. A central ambient monitoring station provided daily concentrations of fine particles (PM(2.5), sulfate, elemental carbon) and gases. Sulfate was used as a marker of regional pollution. The authors used logistic mixed effects regression to examine the odds of having any supraventricular ectopy (SVE) or ventricular ectopy (VE) in association with increases in air pollution for moving average pollutant concentrations up to 10 days before the health assessment.

RESULTS

Participant specific mean counts of arrhythmia over the protocol varied between 0.1-363 for SVE and 0-350 for VE. The authors observed odds ratios for having SVE over the length of the protocol of 1.42 (95% CI 0.99 to 2.04), 1.70 (95% CI 1.12 to 2.57), and 1.78 (95% CI 0.95 to 3.35) for 10.0 microg/m3, 4.2 microg/m3, and 14.9 ppb increases in five day moving average PM2.5, sulfate, and ozone concentrations respectively. The other pollutants, including elemental carbon, showed no effect on arrhythmia. Participants reporting cardiovascular conditions (for example, previous myocardial infarction or hypertension) were the most susceptible to pollution induced SVE. The authors found no association of pollution with VE.

CONCLUSION

Increased levels of ambient sulfate and ozone may increase the risk of supraventricular arrhythmia in the elderly.

Hypocalcemic Heart Failure in Thalassemic Patients

Hypocalcemic cardiomyopathy in primary or secondary hypoparathyroidism is usually refractory to conventional treatment of cardiac failure. We report the case of a thalassemic patient with severe cardiac failure that might have been attributed to several factors, such as hemosiderosis, hypomagnesemia, and hypocalcemia, refractory to conventional cardiac therapy. Cardiac echocardiography showed impaired biventricular performance, and laboratory analyses revealed hypoparathyroidism due to hemosiderosis. When concomitant treatment of heart failure and calcium supplementation was initiated, correction of hypocalcemia resulted in clinical and laboratory improvement, providing strong evidence in support of our hypothesis about hypocalcemic myocardiopathy.

Intrafamilial variability of noncompaction of the ventricular myocardium

BACKGROUND

Noncompaction of the ventricular myocardium (NVM) is a relatively uncommon form of cardiomyopathy characterized by a highly trabeculated myocardium. This report describes the clinical and genetic evaluation of a 3-generation kindred.

METHODS

Family members were initially evaluated by 2-dimensional echocardiography. Most family members with signs of NVM were further evaluated by magnetic resonance imaging. Genetic analyses included mutational screening of the taffazin (TAZ) and alpha-dystrobrevin (DTNA) genes.

RESULTS

Eight family members had signs of NVM. Considerable interindividual variation was noted in terms of spatial distribution and severity of affected regions and ventricular dysfunction. Depending on which of 2 previously proposed quantitative diagnostic criteria were used and where ventricular myocardial measurements were taken, between 4 and 7 of these individuals had findings that were considered diagnostic. Magnetic resonance imaging served as a useful adjunct for confirming or establishing diagnoses in all 8 individuals. No mutation was found in TAZ or DTNA.

CONCLUSIONS

This kindred demonstrates the remarkably wide phenotypic spectrum that can be seen in familial cases of NVM, ranging from prenatal/neonatal lethality to a complete lack of symptoms. The fact that all 8 affected individuals either have shown improvement in ventricular function or symptoms during childhood or have been asymptomatic indicates that NVM can have a relatively benign course. The degree and nature of cardiac involvement are also quite varied, and there is a weak correlation with ventricular function and symptoms. Evaluation of families with NVM requires careful assessment that uses a combination of imaging techniques and diagnostic criteria.

Biventricular diastolic filling patterns after coronary artery bypass graft surgery

OBJECTIVE

We sought to study the evolution of biventricular filling properties after coronary artery bypass grafting.

BACKGROUND

The evolution of diastolic function as defined with newer echocardiographic modalities after coronary artery bypass grafting surgery is unknown in patients with preoperative left ventricular diastolic dysfunction.

METHODS

Transthoracic echocardiography was performed preoperatively and 48 hours and 6 months after coronary artery bypass grafting in 49 patients (randomized to milrinone [n = 25]) or placebo [n = 24]) with preoperative left ventricular diastolic dysfunction classified according to published criteria. Mild right ventricular diastolic dysfunction was defined as the ratio of early to atrial filling velocity of less than 1 in transtricuspid flow or the velocity of reversed atrial flow of greater than 50% of that of systolic flow in hepatic venous flow or the ratio of tricuspid annulus velocity during early and atrial filling of less than 1 if both the ratio of early to atrial filling velocity and the ratio of systolic to diastolic velocity was greater than 1 in hepatic venous flow. Moderate right ventricular diastolic dysfunction was diagnosed when there was a ratio of early to atrial filling velocity of greater than 1 with a ratio of systolic to diastolic velocity of less than 1. Severe right ventricular diastolic dysfunction was defined as a ratio of early to atrial filling velocity of greater than 1 associated with reversed systolic wave in hepatic venous flow.

RESULTS

Moderate and severe left ventricular diastolic dysfunction increased from preoperatively to 48 hours after coronary artery bypass grafting from 8.2% to 53.7% and from 2.0% to 9.7%, respectively (P < .0001, 48 hours vs preoperatively for both), and the patterns at 6 months were similar to those observed preoperatively. Similar evolution over time was found for right ventricular diastolic dysfunction.

CONCLUSIONS

In patients with preoperative left ventricular diastolic dysfunction, biventricular filling patterns are impaired initially but return to preoperative status 6 months after coronary artery bypass grafting.

Diastolic dysfunction in stunned myocardium: a state of abnormal excitation–contraction coupling that is limited by Na+–H+ exchange inhibition

OBJECTIVE

The systolic and diastolic effects of myocardial stunning were studied to evaluate the contributions of the endocardial and epicardial segments of the ventricular myocardial band, and determine if preconditioning by Na+-H+ exchange (NHE) inhibition effected post-stunning dysfunction.

METHODS

Thirteen Yorkshire-Duroc pigs (27.3-38.2 kg) underwent 15 min of mid-LAD clamping. Seven had no protective measures and six were pretreated with IV Cariporide 5 mg/kg 15 min before ischemia. Sonomicrometer crystals evaluated systolic dysfunction (impaired regional shortening) and diastolic dysfunction (contraction extending into early diastole).

RESULTS

Before ischemia, contraction started first on the endocardial side followed 82+/-23 ms later by the subepicardium. Endocardial shortening stopped first, coinciding with negative dP/dt onset, while epicardial shortening phase persisted for 92+/-33 ms more during occurrence of rapid LVP descent and development of peak negative dP/dt. Ischemia produced paradoxical bulging of both segments. Sixty minutes after ischemia systolic segment shortening recovered 36+/-24% of baseline values without pretreatment, compared to 75.8+/-15% with Cariporide (p<0.05). Global ejection force (maximum dP/dt) fell 32+/-20% in the unprotected group, but was maintained by Cariporide pretreatment. Diastolic dysfunction always showed continued endocardial contraction into early diastole (occupying 38+/-16% of diastole in untreated hearts), whereas Cariporide treatment reduced this dysfunction to 5+/-10% (p<0.05). Persistent diastolic dysfunction raised left ventricle end diastolic pressure (LVEDP) 4 mmHg in untreated hearts, whereas Cariporide returned LVEDP to normal. Less elevation of creatine kinase MB (CK-MB) and conjugated dienes followed Cariporide pretreatment.

CONCLUSIONS

Temporary LAD ischemia alters the normal sequential pattern of contraction responsible for ejection and suction by (a) reducing systolic contractile force, and (b) prolonging endocardial contraction into early diastole to disrupt the normal endocardial-epicardial sequence responsible for ventricular suction. NHE inhibition before ischemia limits postischemic systolic and diastolic dysfunction by re-establishing the expected shortening sequences within the ventricular myocardial band model.

Impaired left ventricular filling due to right-to-left ventricular interaction in patients with pulmonary arterial hypertension

The aim of this study was to investigate the contribution of direct right-to-left ventricular interaction to left ventricular filling and stroke volume in 46 patients with pulmonary arterial hypertension (PAH) and 18 control subjects. Stroke volume, right and left ventricular volumes, left ventricular filling rate, and interventricular septum curvature were measured by magnetic resonance imaging and left atrial filling by transesophageal echocardiography. Stroke volume, left ventricular end-diastolic volume, and left ventricular peak filling rate were decreased in PAH patients compared with control subjects: 28 ± 13 vs. 41 ± 10 ml/m2( P < 0.001), 46 ± 14 vs. 61 ± 14 ml/m2( P < 0.001), and 216 ± 90 vs. 541 ± 248 ml/s ( P < 0.001), respectively. Among PAH patients, stroke volume did not correlate to right ventricular end-diastolic volume or mean pulmonary arterial pressure but did correlate to left ventricular end-diastolic volume ( r = 0.62, P < 0.001). Leftward interventricular septum curvature was correlated to left ventricular filling rate ( r = 0.64, P < 0.001) and left ventricular end-diastolic volume ( r = 0.65, P < 0.001). In contrast, left atrial filling was normal and not correlated to left ventricular end-diastolic volume. In PAH patients, ventricular interaction mediated by the interventricular septum impairs left ventricular filling, contributing to decreased stroke volume.

Increased Intra-QRS Fragmentation in Magnetocardiography as a Predictor of Arrhythmic Events and Mortality in Patients with Cardiac Dysfunction After Myocardial Infarction

INTRODUCTION

Increased intra-QRS fragmentation score (FRA) in magnetocardiography (MCG) has shown association with sustained ventricular arrhythmias in post-MI patients suggesting its relation to arrhythmia substrate. The aim of this study was to investigate whether increased FRA in MCG predicts arrhythmic events and mortality after acute myocardial infarction (MI) with cardiac dysfunction.

METHODS AND RESULTS

A series of 158 patients with acute MI and left ventricular ejection fraction (LVEF) <50% were studied. Their age was 60 +/- 10 years and LVEF 40 +/- 6%. MCG was registered and FRA was computed. For comparison, QRS duration in 12-lead ECG was measured. In a mean follow-up of 50 +/- 15 months, 32 (20%) patients died and 18 (11%) had an arrhythmic event. Both arrhythmic event rate and all-cause mortality were significantly higher in patients with increased FRA (P < 0.001 for both). In contrast, increased QRS duration in ECG predicted all-cause mortality (P < 0.05) but not arrhythmic events. In multivariate analysis, FRA was an independent predictor of both arrhythmic events and all-cause mortality. Using a combined criterion of increased FRA and LVEF < 30% yielded positive and negative predictive accuracies of 50% and 91% for arrhythmic events.

CONCLUSION

In post-MI patients with left ventricular dysfunction, increased intra-QRS fragmentation in high-resolution magnetocardiography predicts arrhythmic events, whereas QRS duration in 12-lead ECG predicts all-cause mortality. Analysis of intra-QRS fragmentation by MCG may assist in guiding therapy of post-MI patients, for example, by selecting those who would benefit most from prophylactic implantable cardioverter-defibrillator therapy.

Monocyte chemoattractant protein-1 induces a novel transcription factor that causes cardiac myocyte apoptosis and ventricular dysfunction

Monocyte chemoattractant protein-1 (MCP-1; CCL2)-mediated inflammation plays a critical role in the development of ischemic heart disease (IHD). However, the gene expression changes caused by signal transduction, triggered by MCP-1 binding to its receptor CCR2, and their possible role in the development of IHD are not understood. We present evidence that MCP-1 binding to CCR2 induces a novel transcription factor (MCP-induced protein [MCPIP]) that causes cell death. Gene microarray analysis showed that when expressed in hiuman embryonic kidney 293 cells, MCPIP induced apoptotic gene families before causing cell death. Mutagenesis studies showed that the structural features required for transcription factor-like activity were also required for causing cell death. Activation of caspase-3 was detected after MCPIP transfection and Z-VAD-fmk partially inhibited cell death. Cardiomyocyte-targeted expression of MCP-1 in mice caused death by heart failure at 6 months of age. MCPIP expression increased in parallel with the development of ventricular dysfunction. In situ hybridization showed the presence of MCPIP transcripts in the cardiomyocytes and immunohistochemistry showed that MCPIP was associated with the cardiomyocyte nuclei of apoptotic cardiomyocytes. CCR2 expression in cardiomyocytes increased with the development of IHD. MCPIP production induced by MCP-1 binding to CCR2 in the cardiomyocytes is probably involved in the development of IHD in this murine model. MCPIP transcript levels were much higher in the explanted human hearts with IHD than with nonischemic heart disease. These results provide a molecular insight into how chronic inflammation and exposure to MCP-1 contributes to heart failure and suggest that MCPIP could be a potential target for therapeutic intervention.

Diastolic asynchrony is more frequent than systolic asynchrony in dilated cardiomyopathy and is less improved by cardiac resynchronization therapy

OBJECTIVES

To compare the incidence of diastolic and systolic asynchrony, assessed by tissue Doppler imaging (TDI), in patients with congestive heart failure (CHF) and severe left ventricular (LV) dysfunction, and to assess TDI changes induced by cardiac resynchronization therapy (CRT).

BACKGROUND

Thirty percent of CRT candidates are nonresponders. Besides QRS width, the presence of echographic systolic asynchrony has been used to identify future responders. Little is known about diastolic asynchrony and its change after CRT.

METHODS

Tissue Doppler imaging was performed in 116 CHF patients (LV ejection fraction 26 +/- 8%). Systolic and diastolic asynchrony was calculated using TDI recordings of right ventricular and LV walls.

RESULTS

The CHF group consisted of 116 patients. Diastolic asynchrony was more frequent than systolic, concerning both intraventricular (58% vs. 47%; p = 0.0004) and interventricular (72 vs. 45%; p < 0.0001) asynchrony. Systolic and diastolic asynchrony were both present in 41% patients, but one-third had isolated diastolic asynchrony. Although diastolic delays increased with QRS duration, 42% patients with narrow QRS presented with diastolic asynchrony. Conversely, 27% patients with large QRS had no diastolic asynchrony. Forty-two patients underwent CRT. Incidence of systolic intraventricular asynchrony decreased from 71% to 33% after CRT (p < 0.0001), but diastolic asynchrony decreased only from 81% to 55% (p < 0.0002). Cardiac resynchronization therapy induced new diastolic asynchrony in eight patients.

CONCLUSIONS

Diastolic asynchrony is weakly correlated with QRS duration, is more frequent than systolic asynchrony, and may be observed alone. Diastolic asynchrony is less improved by CRT than systolic. Persistent diastolic asynchrony may explain some cases of lack of improvement after CRT despite good systolic resynchronization.

Magnetic resonance imaging assessment of ventricular dyssynchrony: current and emerging concepts

Despite the numerous documented benefits of cardiac resynchronization therapy (CRT), a significant proportion of patients undergoing CRT do not demonstrate symptomatic or morphologic improvement, triggering the search to improve targeting of this therapy. Many studies now support direct assessment of mechanical dyssynchrony as a method to better identify CRT responders. Among the methods used, echo-Doppler imaging has taken center stage and is covered in other articles in this special issue; however, these methods have several inherent limitations, and other alternatives are also being explored such as magnetic resonance imaging (MRI). This review discusses the concepts and clinical use of MRI methods for quantitative assessment of mechanical dyssynchrony, highlighting newer acquisition and analysis methods and focusing on how the data can be synthesized into robust indexes of dyssynchronous heart failure.

Diastolic dysfunction and pulmonary hypertension in sickle cell anemia: is there a role for L-carnitine treatment?

Clinical manifestations of cardiovascular abnormalities in patients with sickle cell (SC) anemia are well documented. Many variables were assessed in our study before and after administration of L-carnitine to randomly selected 37 SC disease (SCD) children for a period of 6 months. Variables such as weight, height, serum ferritin levels, units of blood transfused and the number of veno-occlusive crises all showed significant improvement after the 6 months of therapy with L-carnitine. Our study also showed that cardiac diastolic function and pulmonary hypertension are common in pediatric SCD patients. These two disorders showed some improvement after L-carnitine administration. Therefore, L-carnitine deserves a rigorous large-scale randomized clinical trial to evaluate its potential benefits as treatment for SCD patients with cardiac complications.

Perioperative management of patients with poorly functioning ventricles in the setting of the functionally univentricular heart

The patient with a functionally univentricular heart is at increased risk for ventricular dysfunction for a variety of reasons. At birth, the pulmonary and systemic circulations are in parallel, leading to pulmonary overcirculation and a volume-loaded functional ventricle. Significant atrioventricular valvar regurgitation, abnormal ventriculoarterial coupling, diastolic dysfunction, and altered ventricular geometry can also contribute to long-term ventricular dysfunction. These collected circumstances place the patient at increased risk for perioperative morbidity and mortality. We will discuss in this review the pathophysiology that leads to ventricular dysfunction at each stage of surgical palliation, as well as the strategies for perioperative management. In addition, we will highlight novel strategies for management of ventricular dysfunction.

Mechanical support of the functionally single ventricle

Children with a functionally single ventricle constitute just over 1% of congenital cardiac defects.1A majority of children with the functionally univentricular circulation undergo a three-staged reconstruction to achieve completion of the Fontan circulation. The first stage is usually performed in the neonatal period, and is either banding of the pulmonary trunk, an aorto-pulmonary shunt alone, or the shunt included as part of the first stage of reconstruction. In recent years, a conduit placed from the right ventricle to the pulmonary arteries is being used as an alternate source of flow of blood to the lungs. The second stage is the bidirectional cavopulmonary anastomosis, the two surgical variations being the so-called “hemifontan”, and “bidirectional Glenn” procedures, while the third stage is the completion of the Fontan circulation, the two surgical variations being either construction of a lateral tunnel, or placement of an extra-cardiac conduit, each being possible with or without a fenestration. In many centres, patients with the functionally univentricular circulation make up one-fifth of the total surgical volume. The syndrome of low cardiac output is quite common in this population through all three stages of reconstruction, and some of these patients will eventually require cardiac transplantation. While conventional therapy, with inotropic support and afterload reduction, remains the mainstay of therapy for the failing heart in children, mechanical support is being increasingly used.3Most of this experience is limited to extracorporeal membrane oxygenation.2–5In this review, we discuss the current experiences with extracorporeal membrane oxygenation in patients with a functionally univentricular circulation, and describes some of their unique features. We also focus on the pulsatile ventricular assist devices capable of providing support over the longer term, and other new devices that may have a role in the future in these patients.6

Metalloproteinase inhibitor counters high-energy phosphate depletion and AMP deaminase activity enhancing ventricular diastolic compliance in subacute heart failure

Cardiac matrix metalloproteinases (MMPs) stimulated by the sympathomimetic action of angiotensin II (AII) exacerbate chamber diastolic stiffening in models of subacute heart failure. Here we tested the hypothesis that MMP inhibition prevents such stiffening by favorably modulating high-energy phosphate (HEP) stores more than by effects on matrix remodeling. Dogs were administered AII i.v. for 1 week with tachypacing superimposed in the last two days (AII+P; n = 8). A second group (n = 9) underwent the same AII+P protocol but was preceded by oral treatment with an MMP inhibitor PD166793 [(S)-2-(4-bromo-biphenyl-4-sulfonylamino-3-methyl butyric acid] 1 week before and during the AII+P period. Pressure-volume analysis was performed in conscious animals, and myocardial tissue was subjected to in vitro and in situ zymography, collagen content, and HEP analysis (high-performance liquid chromatography). As reported previously, AII+P activated MMP9 and MMP2 and specifically exacerbated diastolic stiffening (+130% in chamber stiffness). PD166793 cotreatment prevented these changes, although myocardial collagen content, subtype, and cross-linking were unaltered. AII+P also reduced ATP, free energy of ATP hydrolysis (DeltaG(ATP)), and phosphocreatine while increasing free [ADP], AMP catabolites (nucleoside-total purines), and lactate. PD166793 reversed most of these changes, in part due to its inhibition of AMP deaminase. MMP activation may influence cardiac diastolic function by mechanisms beyond modulation of extracellular matrix. Interaction between MMP activation and HEP metabolism may play an important role in mediating diastolic dysfunction. Furthermore, these data highlight a potential major role for increased AMP deaminase activity in diastolic dysfunction.