Left ventricular performance following the arterial switch operation: use of noninvasive wall stress analysis in the postoperative period

Post-operative troponin levels and left ventricular function in patients with d-transposition of the great arteries following the arterial switch operation

The aim of this study was to assess the significance of post-operative troponin levels as a surrogate for left ventricular (LV) dysfunction measured by global longitudinal strain (GLS) in patients with dextro-transposition of the great arteries (d-TGA) who undergo an arterial switch operation (ASO), and to explore the LV GLS recovery in the mid-term follow-up period. Seventy-eight neonates were included, of whom 41 had troponin-I measurements and 37 had troponin-T measurements. The primary outcome of LV GLS was assessed and compared with healthy controls at the pre-operative stage and time of discharge, 3 months, 6 months and 12 months of age. Secondary outcomes included deaths or transplantations and other clinical markers such as length of hospital stay. D-TGA patients had worse LV GLS post-operatively compared to age-matched controls (p < 0.01) which improved by 12 months of age (p = 0.53). No association was found between changes in troponin-I or troponin-T levels and LV GLS at the time of discharge (r = 0.4, p = 0.64 and r = -0.5, p = 0.91, respectively). In addition, there were no deaths or transplantations in this cohort over a period of 12 months. LV GLS appears to worsen in the early post-operative period for d-TGA patients who undergo neonatal ASO but this recovers through the first post-operative year. Troponin levels have limited value in predicting early or midterm LV dysfunction and recovery.

The clinical value of ultrasonic cardiac output monitor in very-low birth-weight and extremely-low-birth-weight infants undergoing PDA ligation

BACKGROUND

Cardiorespiratory instability occurs very often in very-low-birth-weight (VLBW) and extremely-low-birth-weight (ELBW) infants undergoing patent ductus arteriosus (PDA) ligation during the early postoperative period. This study aimed to investigate ultrasonic cardiac output monitor (USCOM) as a bedside tool by evaluating the hemodynamic changes in preterm infants following PDA ligation and assessing factors that may influence these changes.

METHODS

This was a single-center prospective observational study at a third-level neonatal intensive care unit. A total of 33 infants, including 21 VLBW and 12 ELBW infants, were involved. Hemodynamic measurements were performed in these infants using a USCOM preoperatively as well as 0-1 h, 8-10 h, and 24 h postoperatively.

RESULTS

The PDA ligation was associated with reductions of the left ventricular cardiac output (LVCO) (P < 0.001), cardiac index (P < 0.001), flow time corrected (FTC) (P < 0.001), Smith-Madigan inotropy index (SMII) (P < 0.001), oxygen delivery (DO₂) (P < 0.001), and oxygen delivery index (DO₂I) (P < 0.001) and an increase of the systemic vascular resistance index (SVRI) (P < 0.001) at 0-1 h, 8-10 h, and 24 h post-ligation compared with the respective preoperative values. Compared with the respective values at 0-1 h post-ligation, there was no significant difference in the CI, SMII, or FTC at 8-10 h and 24 h post-ligation. However, the SVRI decreased at 8-10 h and 24 h post-ligation. Moreover, the DO₂I increased at 8-10 h and 24 h post-ligation, and the LVCO and DO₂ increased at 24 h post-ligation.

CONCLUSION

Our study confirmed that the hemodynamic changes measured by the USCOM were similar to those measured by echocardiography in previous reports. Thus, USCOM is a useful and convenient bedside tool for assessing hemodynamic changes to guide the use of fluids, inotropic agents, and vasopressors and help modify the post-ligation course, and they may be a surrogate for repeated echocardiography during the early post-ligation period in preterm infants or a preliminary screening method.

Measurement of inotropy and systemic oxygen delivery in term, low- and very-low-birth-weight neonates using the Ultrasonic Cardiac Output Monitor (USCOM)

Background The aim of this study was to assess the normal values of the Smith-Madigan inotropy index (SMII) and oxygen delivery index (DO2I) in low-birth-weight (LBW) and very-low-birth-weight (VLBW) newborns on the first 3 days of life, and to identify how different degrees of maturity influence cardiovascular alterations during the transitional period compared with term neonates. Methods Twenty-eight VLBW newborns, 46 LBW newborns and 50 normal full-term newborns admitted to our department were studied. Hemodynamics of the left heart were measured in all neonates over the first 3 days using the Ultrasonic Cardiac Output Monitor (USCOM). This was combined with hemoglobin concentration and pulse oximetry to calculate DO2I. Blood pressure was combined with the hemodynamic measures and hemoglobin concentration to calculate SMII. Results SMII showed statistically significant differences among the three groups (VLBW 0.48 ± 0.11; LBW 0.54 ± 0.13; term 0.69 ± 0.17 W/m2 P < 0.001), which was in line with the following myocardial parameters: stroke volume index (SVI) and cardiac index (CI) (P < 0.001 and <0.001). For systemic oxygen delivery (DO2) parameters, significant differences were found for DO2I (P < 0.001) while hemoglobin concentration and pulse oximetry demonstrated no significant differences. In the VLBW group, SMII and DO2I showed no significant change over the 3 days. Conclusion Normal inotropy and systemic DO2I values in VLBW neonates over the first 3 days of life were assessed. SMII and DO2I were significantly lower in VLBW neonates during the first 72 h of life. With increasing birth weight, higher myocardial inotropy and DO2 were found. The addition of USCOM examination to standard neonatal echocardiography may provide further important information regarding cardiac function.

Ventricular performance after surgery for a congenital heart defect as assessed using advanced echocardiography: from doppler flow to 3D echocardiography and speckle-tracking strain imaging

A varying degree of impairment of ventricular performance is observed over the long-term after surgery for a congenital heart defect (CHD). Impaired ventricular performance has been shown to be of prognostic value for increased risk of cardiovascular events in adult CHD patients. This emphasizes the importance of delineating the timing and cause of this postoperative impairment. Impairment of ventricular performance could develop over time as a consequence of residua, sequelae and complications of the CHD or surgical procedure. Yet, impaired ventricular performance has also been observed immediately after surgery and can persist and/or worsen over time. This postoperative impairment of ventricular performance is the focus of this review. This article provides an overview of echocardiographic techniques currently used to assess ventricular performance. Furthermore, we review current literature describing ventricular performance, as assessed using echocardiography, after correction of a CHD. In general, a decrease in ventricular performance is observed directly after surgery for CHD’s. Subsequent follow-up of ventricular performance is characterized by a varying degree of postoperative recovery. A consistent observation is the persistent impairment of right-ventricular performance after repair in several different subgroups of CHD patients ranging from ventricular septal defect repair to surgery for Tetralogy of Fallot.

Measurement of systemic oxygen delivery and inotropy in healthy term neonates with the Ultrasonic Cardiac Output Monitor (USCOM)

INTRODUCTION

The aim of this study was to assess the normal values for Smith-Madigan inotropy (SMI), Smith-Madigan inotropy index (SMII), oxygen delivery (DO2) and oxygen delivery index DO2I in healthy term neonates on the first day of life and during circulatory adaptation over the first three days of life.

METHODS

Hemodynamics of the left heart were measured non-invasively in 71 normal full-term neonates over the first three days using the Ultrasonic Cardiac Output Monitor (USCOM). This was combined with hemoglobin concentration from umbilical cord blood and pulse oximetry to calculate DO2 and DO2I. Blood pressure was measured using automated oscillometry and combined with the hemodynamic measures and hemoglobin concentration using the Smith-Madigan method to calculate inotropy (SMI) and inotropy index (SMII).

RESULTS

SMI and SMII showed no significant change during the study period, ranging from 154 to 168 mW and 694 to 731 mW/m(2). Mean (SD) DO2 and DO2I showed a significant fall over three days from 131 (63) ml/min and 596 (278) ml/m(2)/min to 118 (46) ml/min and 517 (173) ml/m(2)/min (p<0.01 and <0.001 respectively) with a corresponding decrease in cardiac output from 758 (143) ml/min to 658 (131) ml/min, (p=0.002). There was no significant change in stroke volume, heart rate, SMI or SMII within the first day. DO2 and DO2I showed small but significant decreases within the first day from 153 (46) ml/min and 699 (174) ml/min/m(2) to 129 (36) ml/min and 609 (141) ml/min/m(2) (p=0.017 and 0.048 respectively).

CONCLUSIONS

Normal inotropy of the left heart and systemic DO2 values in healthy full-term neonates over the first three days of life were assessed using the USCOM. Subjects showed stable myocardial contractility over the first three days with decreasing DO2 and DO2I in line with the decrease in cardiac output (CO). DO2 and DO2I showed small but significant reductions during the first 24 h. USCOM proved to be a feasible and convenient non-invasive bedside tool to assess inotropy and oxygen delivery in neonates.

Echocardiography as a hemodynamic monitor in critically ill children

Echocardiography is a widely used modality to assess myocardial structure and function in pediatric intensive care settings. While the use of echocardiography for diagnostic purposes remains important, its use as a hemodynamic monitoring tool has not been well established. The benefits of echocardiography are in its widespread availability, relative ease of use, and importance in diagnosing structural disease and simple changes in myocardial function. However, echocardiography in pediatric critical care is limited in its use because it requires the acquisition of quality images and the accurate interpretation of the study. To date, the literature on echocardiography in pediatric critical care is limited. The purpose of this review is to examine the scientific evidence for the usefulness of echocardiography as a hemodynamic monitoring tool in pediatric critical care.

Comparison of classifications for heart failure in children undergoing valvular surgery

OBJECTIVES

To characterize correlations between clinical classifications of heart failure and diagnostic workup.

STUDY DESIGN

Pre- and postoperative characteristics of 20 children with heart failure secondary to valvular rheumatic disease were studied.

RESULTS

Both scoring systems correlated with N-terminal pro-brain natriuretic peptide (N-proBNP) but not with troponin I (TnI). The PHFI correlated with N-proBNP, end-systolic wall stress, left ventricular mass index and left atrium to aorta diameter ratio. No correlation could be established between modified Ross score, or the New York Heart Association (NYHA) grade and echocardiographic measurements. Cardiothoracic and Sokolow indexes were correlated with the PHFI as well as to the NYHA classification.

CONCLUSION

In this study, PHFI seems better correlated with radiologic, electrocardiographic, echocardiographic, and biologic assessment of heart failure in children. Clinical severity was correlated with N-proBNP but not with TnI.

Evidence of adverse ventricular interdependence in patients with atrial septal defects

Right ventricular (RV) volume overload is associated with left ventricular (LV) distortion and dysfunction. The availability of transcatheter device closure of secundum atrial septal defect (ASD) provides an ideal model for investigating the immediate effects of elimination of RV volume overload and avoiding the confounding effects of surgery on LV function. Echocardiograms before and after device closure of ASD were analyzed for ejection fraction, percent changes in cross-sectional area and circumference, percent changes in free wall and septal endocardial lengths, and eccentricity. We enrolled 34 patients (median age 9 years) who underwent device closure of ASD (pulmonary to systemic shunt 1.6 +/- 0.4). Ejection fraction and LV end-diastolic volume, reflective of chamber preload, were significantly decreased in the presence of RV volume overload and normalized after defect closure with normalization of LV shape. Altered LV geometry secondary to RV volume overload was associated with regional variation in preload,such that diastolic circumference, a surrogate of myofiber preload, increased after closure of ASD secondary to a small increase in LV free wall arc length in conjunction with a much more significant increase in septal length. Thus, LV dysfunction associated with RV volume overload is secondary to altered chamber geometry and decreased myofiber preload. This physiology is immediately reversible and is independent of heart rate and afterload.

Echocardiographic Assessment of the Right Ventricular Stress-Velocity Relationship Under Normal and Chronic Overload Conditions

The effects of chronic volume or pressure overload on the velocity of right ventricular ejection have not been previously well defined. We hypothesized that, as formerly shown for the left ventricle, there would be a direct relationship between the velocity of ejection and an estimate of systolic wall stress.

METHODS

Echocardiograms of asymptomatic patients, not on cardiac medications, with either an isolated secundum atrial septal defect > or = 5 mm in diameter or isolated pulmonic stenosis with a peak instantaneous pressure gradient > or = 20 mmHg, were reviewed. Forty-one patients with an atrial septal defect and 34 with pulmonary stenosis met criteria, and were compared to age-matched normal controls. Total subjects were 127 with ages ranging from 1 day to 54 years. Right ventricular monoplane ejection fraction, ejection time corrected for heart rate (ETc), mean normalized systolic ejection rate (MNSERc) and meridianal peak-systolic wall stress (WSps) were measured.

RESULTS

Compared to controls, ejection fractions were not significantly different, but WSps averaged 81% and 110% higher, ETc 8% and 9% longer, and MNSERc 5% and 9% slower in the atrial septal defect and pulmonary stenosis groups, respectively. Among all subjects WSps had a significant linear correlation with ETc (r = 0.61, P < 0.01), MNSERc (r =-0.46, P < 0.01), and ejection fraction (r =-0.19, P < 0.05).

CONCLUSIONS

Increases in WSps cause an incremental slowing of MNSERc in the right ventricle, with a relationship that is linear over a wide range of normal and abnormal loading conditions.

Monitoring cardiac function in intensive care

Systolic cardiac function results from the interaction of four interdependent factors: heart rate, preload, contractility, and afterload. Heart rate can be quantified easily at the bedside, while preload estimation has traditionally relied on invasive pressure measurements, both central venous and pulmonary artery wedge. These have significant clinical limitations; however, adult literature has highlighted the superiority of several novel preload measures. Measurement of contractility and afterload is difficult; thus in clinical practice the bedside assessment of cardiac function is represented by cardiac output. A variety of techniques are now available for cardiac output measurement in the paediatric patient. This review summarises cardiac function and cardiac output measurement in terms of methodology, interpretation, and their contribution to the concepts of oxygen delivery and consumption in the critically ill child.

Measurement of cardiac output and tissue perfusion

Recent technologic innovations have allowed a greater scope for cardiac output measurement in critically ill children. There is a move toward both less invasive and continuous methods, several of which also offer novel measures of preload. Many of the new methods are still undergoing preliminary evaluation in the pediatric population and will be summarized in this article.

Impaired urinary cortisol excretion and early cardiopulmonary dysfunction in immature baboons

Early adrenal insufficiency is associated with cardiopulmonary dysfunction in immature infants. Isolated cortisol levels and ACTH stimulation testing may not adequately show ontogeny of postnatal cortisol secretion nor identify at risk infants. Our objectives were 1) to determine postnatal urinary cortisol excretion rate (UCER) from birth to 14 d in immature baboons and 2) to evaluate the relation between UCER and cardiac performance. UCER was assessed via 6-h blocked urine collections from birth to 336 h of age in twenty-one 125-d gestation (term = 185 d) baboons. Urinary cortisol was measured by RIA. Cardiopulmonary parameters were averaged over the same time periods as urine collection. Serial two-dimensional echocardiograms were performed. After 24-h age, a subgroup (n = 8) received up to four doses (0.5-1.0 mg/kg each) of hydrocortisone for refractory hypotension. UCER significantly increased from 0 to 6 h through 66 to 72 h age for non-cortisol-treated infants. Significantly reduced UCER patterns between birth and 24 h were found for animals subsequently requiring cortisol treatment. Cortisol-treated infants had lower mean blood pressure, worse metabolic acidosis, increased fluid needs, and impaired left ventricular function between 12 and 48 h of age. No group differences were found in gas exchange or ventilator support. We conclude that adrenal cortisol secretion significantly improves over the initial 72 h of life in the 125-d immature baboon. Failure to increase UCER after 12-24 h of life correlated with poor cardiovascular function that improved with hydrocortisone therapy. Adrenal hypofunction in the immature baboon is similar to the very preterm human and could serve as a model for future postnatal investigations.

Clinical applications of wall-stress analysis in the pediatric intensive care unit

OBJECTIVE

To determine whether serial, noninvasive assessment of afterload, contractility, and Doppler-derived cardiac output reliably detects variations in cardiac function in unstable pediatric patients.

DESIGN

Prospective, blinded clinical trial.

SETTING

The pediatric intensive care unit at Massachusetts General Hospital.

PATIENTS

Fourteen critically ill pediatric patients.

INTERVENTIONS

Pediatric patients meeting criteria for hemodynamic instability underwent serial echocardiograms every 6 hrs until they met exit criteria, generating 75 studies.

MEASUREMENTS AND MAIN RESULTS

Shortening fraction, cardiac index (CI), end-systolic wall stress (ESWS), and corrected velocity of circumferential shortening (Vcfc) were measured in each patient. Data points were plotted as a stress-velocity relationship, compared with published normal values, then correlated with changes in vital signs and pharmacologic interventions. Fourteen of 16 patients who were enrolled completed the study. A strong negative correlation between ESWS and Vcfc was confirmed (p < .001). As an internal measure of validity, Vcfc had a strong positive correlation with CI measurements (p = .012). An increase in dopamine infusion was associated with a fall in ESWS (p = .02), an increase in Vcfc (p = .03), and an increase in the CI as measured by Doppler (p = .035). The infusion of dopamine above renal perfusion levels moved patients from zones of normal or compensated contractility for afterload on a modified stress-velocity relationship to a zone of high contractility for afterload. Urine output was the only clinical index of cardiac function that had a significant correlation with the echocardiographic indices. Hemodynamically unstable patients followed similar patterns of deterioration and recovery on the modified stress-velocity graph. All surviving patients returned to a normal or compensated zone.

CONCLUSIONS

Wall-stress analysis of cardiac function is easily and safely performed on mechanically ventilated pediatric patients with the production of consistently high-quality data. For internal validity, Vcfc and CI measurements were correlated and were strongly positive. Wall-stress indices reliably detected patient deterioration, recovery, and response to changes in dopamine infusion. Patients who failed to return to areas of normal or compensated levels of contractility and afterload did poorly in this study. Noninvasive measures of afterload and contractility appear useful for monitoring cardiac function of critically ill children in an intensive care setting.