The Imaging Program at the 7th World Congress highlighted the versatility and diagnostic power of the current and upcoming imaging tools in Pediatric Cardiology and Cardiac Surgery. Several experts presented interesting as well as practical data on the use of 2D and 3D Echocardiography, magnetic resonance imaging and computed tomography in the fetus, child, and adult with congenital heart disease. Bridging sessions coupled use of these imaging modalities and screening practices in patients with acquired heart disease. Hot topics included nomenclature of ventricular septal defects, the challenging diagnosis of double outlet right ventricle, cardiac tumors, and imaging of aortapathies. Several talks concentrated on the quantitative assessment of ventricular function and reviewed numerous exciting new modalities that currently serve as research tools. In summary, Imaging Sessions truly represented how far we have advanced the field of Imaging in Pediatric Cardiology and Cardiovascular Surgery.

We studied 11 patients with pulmonary atresia and intact ventricular septum who died at ages ranging from one day to three years. All but two neonates died after surgery. Pre-surgical catheterization with left and right cineventriculography was performed in nine patients, and quantitative parameters were calculated. By histologic examination of transverse transmural sections, the incidence and extent of myocardial ischemia or infarction were determined, as well as the percentage area per field occupied by vessels, myocytes orientated longitudinally or transversely, interstitial space, and disarrayed fibers. Comparable sections were obtained from six normal neonates to constitute a control group. Myocardial ischemia or infarction were frequent complications. Morphometric analysis demonstrated a significant difference between the control group and the patients with regard to the percentage of myocytes (longitudinal and transverse), the percentage of area occupied by myocardial disarray, and the presence of fibrosis. The highest values for the proportion of disarray were seen in those patients with small right ventricles. The percentage of myocytes varied, but the highest degree of disarray always correlated with the lowest percentage of myocytes. The highest percentage value of left ventricular disarray was associated with the lowest ratio of left ventricular mass to end diastolic volume (inadequate hypertrophy). The lowest indices of contractility and left ventricular pump function were associated with myocytes less than 55% of normal. A linear correlation was found between the percentage area of fibrosis and the ratio of systolic pressure to end systolic volume in the left ventricle, arid between fibrosis and ejection fraction. Values for fibrosis exceeding 15% were associated with decreased functional indices. Disarray, therefore, seems to express a primary inability of myocardium to respond to anomalous overload with adequate hypertrophy and/or hyperplasia.

The development of newer, load-independent indices of contractility has not substantially reduced general clinical reliance on ejection fraction and shortening fraction to detect abnormalities of contractility, in spite of common understanding of the preload and afterload dependence of percent fiber shortening. The more widespread application of sensitive indices of contractility has been impeded in part by complex methods of acquisition and analysis of data as well as uncertainty concerning the clinical importance of the additional derived information. Substantial recent experience with analysis of stress-shortening and stress-velocity, nonetheless, demonstrates that physiologically meaningful indices of afterload, preload, and contractility can be obtained noninvasively without hemodynamic interventions. There is extensive theoretical and experimental basis for these methods, and the limitations are similar to other global indices of myocardial mechanics. The superiority of methods which allow distinction between contractile abnormalities and abnormal load are particularly important when altered ventricular loading conditions are a prominent feature of the disease state. Several clinical situations have been identified for which analysis of stress-shortening and stress-velocity demonstrates that assessment by fiber shortening alone has resulted in misrepresentation of myocardial status. The clinical utility of assessment of ventricular function is considerably enhanced when the relative contribution of load and contractile performance is determined.

Cross-sectional echocardiography was performed on 108 healthy children (7 days – 17 years old) and 55 children (6 months - 16.5 years old) with interatrial communication. Right ventricular end-diastolic volume, end-systolic volume, stroke volume, ejection fraction, muscle volume, and the ratio of muscle to cavity were calculated on the basis of outlined cavity and myocardium of an apical fourchamber view.

In the normal subjects right ventricular end-diastolic volume, end-systolic volume, stroke volume and muscle volume correlated with body surface area (end-diastolic volume: y=12.5x+7.8x2, r=0.99; end-systolic volume: y=4.8x+3.6x2, r=0.98; stroke volume: y=7.7x+4.2x2, r=0.98; muscle volume: y=14.1x+2.9x2, r=0.97), muscle/cavity ratio (0.85±0.17) and ejection fraction (58.9 ± 6.2%) were unrelated to body surface area. In the subjects with interatrial communication, the right ventricular volumes were significantly larger (p<0.001) than the normal values with a linear relationship to the ratio of pulmonary to systemic flows.

Right ventricular volumes can be determined in normal children with acceptable repeatability using a standard apical four-chamber view. The growth related normal values provide a basis for future quantitative studies.

Using combined epicardial echocardiography and high-fidelity intraventricular pressure recordings, the acute effects of transition to a Fontan circulation were studied in 10 patients. Measurements were made before and after cardiopulmonary bypass. The Fontan operation had no significant effect on load-dependent indices, or on a load independent index (Vmax) of ventricular systolic function. Large changes were observed in ventricular geometry. Maximum and minimum cavity dimensions were reduced, while maximum and minimum thicknesses of the posterior wall were increased.While simultaneous Doppler/intraventricular pressure measurements suggested that the compliance of the ventricle was unchanged, the pattern of atrioventricular flow changed from predominantly early diastolic (E wave) to predominantly atrial systolic (A wave) as a result of surgery in four patients. The time constant of ventricular relaxation was prolonged in all patients and five developed Doppler echocardiographic evidence of incoordinate relaxation of the ventricle, with intraventricular flow occurring during isovolumic relaxation. Thus, the Fontan operation causes acute hypertrophy of the systemic ventricle due to a sudden reduction in ventricular preload in the presence of a maintained shortening fraction. While global ventricular diastolic compliance may be unchanged by the operative procedure, filling of the ventricle during early diastole is altered as a result of incoordinate relaxation and a prolonged time constant of ventricular relaxation.

There has been increasing interest in the study of ventricular function in the patient with congenital heart disease. Numerous indexes have been derived for the assessment of ventricular function, suggesting that none is ideal. While the derivation of some measures of ventricular function have relied on advanced mathematical principles, it is still possible for the non-mathematician to obtain important insights into ventricular function from an assessment of the events which underpin the cardiac cycle. In this review, I use the mechanics of the cardiac cycle to introduce basic concepts of ventricular function for the non-expert. In this way, I analyse ventricular systolic and diastolic performance and describe the contribution of regional variability of function to overall performance. This approach also highlights the role of the ventricle in overall cardiovascular and metabolic homeostasis.

Objective: To study the adaptive potential of the right ventricular myocardium after 30 days of mechanical-induced overload in rats from two different age groups. Materials and methods: We banded the pulmonary trunk, so as to increase the systolic work load of the right ventricle, in 19 adult Sprague-Dawley rats at the age of 10 weeks, and 16 weanlings when they were 3 weeks-old, using 10 adults and 10 weanlings as controls. We analysed the functional adaptation and structural changes of the right ventricular myocardium, blood vessels and interstitial tissue after 30 days of increased afterload. Results: The increased workload induced an increase of the right ventricular weight and free wall thickness in animals from both age groups when compared to controls. These changes were mostly related to cardiomyocytic hypertrophy, as confirmed by the expression of myocardial hypertrophic markers, without any apparent increase of their number, a “reactive” fibrosis especially evident in the adult rats, with p-value less than 0.0001, and a more extensive neocapillary network in the weanlings compared to the adults aubsequent to banding, the p-value being less than 0.0001. Conclusion: In response to right ventricular afterload, weanlings showed a higher adaptive capillary growth, which hampered the development of fibrosis as seen in the adult rats. Age seems to be a risk factor for adverse structural-functional changes of right ventricle subjected to increased workload.

Summary

Background and objective: Measurement of central blood volumes (CBV), such as global end-diastolic volume (GEDV) and right ventricular end-diastolic volume (RVEDV) are considered appropriate estimates of intravascular volume status. However, to apply those parameters for preload assessment in mechanically ventilated patients, the influence of tidal volume (TV) and positive endexpiratory airway pressure (PEEP) on those parameters must be known. Methods: In 13 mechanically ventilated piglets, the effect of low (10 mL kg−1) and high (20 mL kg−1) TVs on CBV was investigated in absence and presence of PEEP (0 and 15 cmH2O). GEDV, RVEDV, right heart (RHEDV) and left heart end-diastolic volume (LHEDV) were measured by thermodilution. Blood flow on the descending thoracic aorta measured with an ultrasonic flow-probe served to determine stroke volume (SV). Measurements were performed during baseline conditions, after volume loading with previously extracted haemodilution blood (20 mL kg−1) and following haemorrhage (30 mL kg−1). Results: Application of PEEP decreased GEDV and SV significantly (P < 0.05). Augmenting TV did not reduce GEDV systematically, but significantly reduced SV (P < 0.05). Changes in ventilator settings only influenced RVEDV following volume loading (P < 0.05). RHEDV and LHEDV decreased following application of PEEP, but only RHEDV decreased after augmenting TV at baseline and following volume loading. Correlation of SV with parameters of CBV was r = 0.487 (P < 0.01) for GEDV, r = 0.553 (P < 0.01) for RVEDV, r = 0.596 (P < 0.01) for RHEDV and r = 0.303 (P < 0.01) for LHEDV. Conclusion: Application of PEEP decreases CBV and SV. Augmenting TV reduces SV but not CBV. There is a moderate correlation between parameters of CBV and cardiac performance.

The identification of the important relationship between shape and function of ventricular chambers represents a milestone of modern cardiology. Application of the law of Laplace for an ideal sphere furnishes intuitive insights on the progression of heart failure. A dilated heart, by virtue of its large size, must generate greater stress in the myocardial wall to achieve sufficient pressure so as to eject the required amount of blood. The mural hypertrophy represents a compensatory mechanism, guaranteeing a lower stress. When the ratio between the radius of the chamber and the thickness of its wall increases abnormally, the heart fails.

Objective: To evaluate the role of the concentration of brain natriuretic peptide in the plasma, and its correlation with haemodynamic right ventricular parameters, in children with overload of the right ventricle due to congenital cardiac disease. Methods: We studied 31 children, with a mean age of 4.8 years, with volume or pressure overload of the right ventricle caused by congenital cardiac disease. Of the patients, 19 had undergone surgical biventricular correction of tetralogy of Fallot, 11 with pulmonary stenosis and 8 with pulmonary atresia, and 12 patients were studied prior to operations, 7 with atrial septal defects and 5 with anomalous pulmonary venous connections. We measured brain natriuretic peptide using Triage®, from Biosite, United States of America. We determined end-diastolic pressures of the right ventricle, and the peak ratio of right to left ventricular pressures, by cardiac catheterization and correlated them with concentrations of brain natriuretic peptide in the plasma. Results: The mean concentrations of brain natriuretic peptide were 87.7, with a range from 5 to 316, picograms per millilitre. Mean end-diastolic pressure in the right ventricle was 5.6, with a range from 2 to 10, millimetres of mercury, and the mean ratio of right to left ventricular pressure was 0.56, with a range from 0.24 to 1.03. There was a positive correlation between the concentrations of brain natriuretic peptide and the ratio of right to left ventricular pressure (r equal to 0.7844, p less than 0.0001) in all patients. These positive correlations remained when the children with tetralogy of Fallot, and those with atrial septal defects or anomalous pulmonary venous connection, were analysed as separate groups. We also found a weak correlation was shown between end-diastolic right ventricular pressure and concentrations of brain natriuretic peptide in the plasma (r equal to 0.5947, p equal to 0.0004). Conclusion: There is a significant correlation between right ventricular haemodynamic parameters and concentrations of brain natriuretic peptide in the plasma of children with right ventricular overload due to different types of congenital cardiac disease. The monitoring of brain natriuretic peptide may provide a non-invasive and safe quantitative follow up of the right ventricular pressure and volume overload in these patients.

The appropriate timing of intervention in patients with chronic aortic incompetence allows recovery of ventricular function. We sought to determine the optimal timing of the Ross procedure for chronic aortic incompetence in young patients. We retrospectively analysed case notes, and measured pre- and postoperative echocardiographic indexes of left ventricular function, in patients who had undergone the Ross procedure for chronic aortic incompetence. Methods and results: We found 21 patients with preoperative and postoperative data suitable for analysis. Their age at operation ranged from 5.6 to 26 years, with a median of 13.8 years, and the duration of follow-up was from 0.5 to 6.8 years, with a median of 2.4 years. The preoperative left ventricular end-diastolic dimension was converted to a z-score, and this was used as a threshold to divide the population. Using the threshold of a preoperative left ventricular z-score of more than 3 to divide the population did not show any difference in postoperative parameters of left ventricular function. Significant differences were found postoperatively, however, in both the left ventricular z-score and the ratio of left ventricular end-diastolic radius to posterior wall thickness in diastole, with a cutoff preoperative threshold z-score greater than 4. Conclusion: The increase in the ratio of left ventricular end-diastolic radius to the thickness of the posterior wall in diastole would suggest that there is disruption of left ventricular short axis architecture and myocardial contractile function when intervention is postponed. The significantly larger left ventricular dimension at end-diastole, despite the reduction in volume loading post surgery, may also demonstrate irreversible structural changes. Our data would suggest that recovery of left ventricular function is less likely when the left ventricular z-score has reached the value of 4, and that, ideally, intervention should be performed when the z-score approaches or exceeds 3.

Summary

Background and objective: To investigate the effects of barbiturates on batrachotoxin-modified sodium channels from different regions of the human heart. Single sodium channels from human atria were studied and compared with existing data from the human ventricle and from the central nervous system.

Methods: Sodium channels from preparations of human atrial muscle were incorporated into planar lipid bilayers in the presence of batrachotoxin, a sodium channel activator. The steady-state behaviour of single sodium channels was recorded in symmetrical 500 mmol NaCl before and after the addition of pentobarbital 0.34–1.34 mmol.

Results: The batrachotoxin-treated human atrial sodium channel had an average single-channel conductance of 23.8 ± 1.6 pS in symmetrical 500 mmol NaCl and a channel fractional open time of 0.83 ± 0.06. The activation mid-point potential was −98.0 ± 2.3 mV. Extracellular tetrodotoxin (a specific sodium channel blocking agent) blocked these channels with a k1/2 = 0.53 μmol at 0 mV. Pentobarbital reduced the time average conductance of single atrial sodium channels in a concentration-dependent manner (ID50 = 0.71 mmol). In the same way, the steady-state activation was shifted to more hyperpolarized potentials (−10.6 mV at 0.67 mmol pentobarbital).

Conclusions: The properties of batrachotoxin-modified sodium channels from human atrial tissue did not differ greatly from those described for ventricular sodium channels in the literature. Our data yielded no explanation for the observed functional diversity. However, cardiac sodium channels differ from those found in the central nervous system.

Background and objective Transoesophageal echocardiography is increasingly used for evaluation and monitoring of left ventricular function in anaesthetized patients. However, the only available reference values for transoesophageal echocardiography were derived from studies in awake subjects.

Methods We determined left ventricular dimensions and systolic function in 45 patients without clinical evidence of heart disease who voluntarily underwent transesophageal echocardiography under conditions of balanced general anaesthesia, controlled fluid administration, supine position, muscle relaxation and controlled ventilation.

Results The left ventricular dimensions obtained during these conditions were lower than the published normal values in awake subjects. The indices of global left ventricular function, however, were similar to the normal values obtained by either awake transesophageal echocardiography or transthoracic echocardiography.

Conclusion We propose using the values obtained in our study as reference values for evaluation of left ventricular function in patients under general anaesthesia and controlled ventilation.

Background and Objective To investigate the response to general anaesthetics of different sodium channel subtypes, we examined the effects of pentobarbital, a close thiopental analogue, on single sodium channels from human ventricular muscle and compared them with existing data from human brain channels.

Methods Sodium channels from preparations of human ventricular muscle were incorporated into planar lipid bilayers in the presence of batrachotoxin, a sodium channel activator. Single channel currents were recorded in symmetrical 100mmolL−1 and 500mmolL−1 NaCl before and after the addition of the anaesthetic pentobarbital (0.34–1.34mmolL−1).

Results The blocking effect of pentobarbital on the fractional open time had an IC50 of 690 μmol L−1 in 500 mmolL−1 NaCl, whereas it had a significantly lower IC50 of 400 μmol L−1 in 100 mmolL−1 NaCl. Pentobarbital caused a significant shift of steady-state activation to hyperpolarized potentials (fmax = −42 mV, IC50=2 mmolL−1). This effect was independent of NaCl concentration.

Conclusion Despite pharmacological and electrophysiological differences between human cardiac and human brain sodium channels their responses to pentobarbital are similar. The finding of channel block being dependent on the electrolyte concentration is novel for sodium channels.

Background and objective Although there is concern that cibenzoline, an antidysrhythmic drug for the treatment of ventricular and supraventricular dysrhy-thmias, may be associated with dose-dependent inhibition of myocardial contractility there are few reports about the relationship between myocardial metabolism and cardiac function when it is used. The present study was designed to investigate the effects of cibenzoline on cardiac function and metabolism. The effects of cibenzoline on cardiac function and myocardial metabolism were assessed in the isolated rat heart-lung preparation.

Methods Thirty-two male Wistar-ST rats were divided into four groups: control, and those to receive cibenzoline, either 300, 900 or 3000 ngmL−1. The cibenzoline was administered into the perfusate 5min after the start of perfusion. Heart rates in the 3000ngmL−1 group were significantly lower than those in the control group. Cardiac output in the 3000 ng mL−1 group at 15 and 30 min was significantly lower than in the control group. In all groups, values for %LV dP/df max (the ratio of values at each time to those at 5 min) at 20, 25, 30 min were significantly higher than at 5min. Myocardial adenosine tripho-sphate concentration in the 3000ngmL−1 group was significantly lower than in controls. There was no difference between groups in the lactate/pyruvate ratio.

Conclusion The therapeutic range of cibenzoline has few effects on cardiac function and metabolism, although concentrations 10 times greater may cause a deterioration in myocardial metabolism.