Myocardial blood flow and coronary flow reserve late after anatomical correction of transposition of the great arteries

Coronary microvascular dysfunction in childhood: An emerging pathological entity and its clinical implications

Coronary microvascular dysfunction (CMD) encompasses a spectrum of structural and functional alterations in coronary microvasculature resulting in impaired coronary blood flow and consequent myocardial ischemia without obstruction in epicardial coronary artery. The pathogenesis of CMD is complex involving both functional and structural alteration in the coronary microcirculation. In adults, CMD is predominantly discussed in context with anginal chest pain or existing ischemic heart disease and its risk factors. The presence of CMD suggests increased risk of adverse cardiovascular events independent of coronary atherosclerosis. Coronary microvascular dysfunction is also known in children but is rarely recognized due to paucity of concommitent coronary artery disease. Thus, its clinical presentation, underlying mechanism of impaired microcirculation, and prognostic significance are poorly understood. In this review article, we will overview variable CMD reported in children and delineate its emerging clinical significance.

Impaired coronary microvascular reactivity in youth with bipolar disorder

BACKGROUND

Cardiovascular disease (CVD) is excessively prevalent and premature in bipolar disorder (BD), even after controlling for traditional cardiovascular risk factors. The increased risk of CVD in BD may be subserved by microvascular dysfunction. We examined coronary microvascular function in relation to youth BD.

METHODS

Participants were 86 youth, ages 13-20 years (n = 39 BD, n = 47 controls). Coronary microvascular reactivity (CMVR) was assessed using quantitative T2 magnetic resonance imaging during a validated breathing-paradigm. Quantitative T2 maps were acquired at baseline, following 60-s of hyperventilation, and every 10-s thereafter during a 40-s breath-hold. Left ventricular structure and function were evaluated based on 12-15 short- and long-axis cardiac-gated cine images. A linear mixed-effects model that controlled for age, sex, and body mass index assessed for between-group differences in CMVR (time-by-group interaction).

RESULTS

The breathing-paradigm induced a significant time-related increase in T2 relaxation time for all participants (i.e. CMVR; β = 0.36, p < 0.001). CMVR was significantly lower in BD v. controls (β = -0.11, p = 0.002). Post-hoc analyses found lower T2 relaxation time in BD youth after 20-, 30-, and 40 s of breath-holding (d = 0.48, d = 0.72, d = 0.91, respectively; all pFDR < 0.01). Gross left ventricular structure and function (e.g. mass, ejection fraction) were within normal ranges and did not differ between groups.

CONCLUSION

Youth with BD showed evidence of subclinically impaired coronary microvascular function, despite normal gross cardiac structure and function. These results converge with prior findings in adults with major depressive disorder and post-traumatic stress disorder. Future studies integrating larger samples, prospective follow-up, and blood-based biomarkers are warranted.

Myocardial Functional Imaging in Pediatric Nuclear Cardiology

The role of nuclear medicine in pediatric cardiology has grown rapidly over the years, providing useful functional and prognostic information and playing a complementary role to morphological imaging in the evaluation of myocardial perfusion, cardiovascular inflammation and infections, and cardiac sympathetic innervation. The aim of this narrative review is to summarize and highlight the most important evidence on pediatric nuclear cardiology, describing clinical applications and the possibilities, advantages, and limitations of nuclear medicine techniques. Moreover, a special focus will be given to the minimization of radiation exposure in pediatric nuclear cardiology imaging, a critical topic in children.

The Use of Stress Cardiovascular Imaging in Pediatric Population

Although not frequent in the pediatric population, ischemia could occur in children due to several congenital and acquired disease. Stress imaging is key for the non-invasive evaluation of myocardial abnormalities and perfusion defect in this clinical setting. Moreover, beyond ischemia assessment, it can provide complementary diagnostic and prognostic information in valvular heart disease and cardiomyopathies. When performed using cardiovascular magnetic resonance, it could detect, in addition, myocardial fibrosis and infarction, increasing the diagnostic yield. Several imaging modalities are currently available for the evaluation of stress myocardial perfusion. Advances in technologies have also increased the feasibility, safety and availability of these modalities in the pediatric age group. However, despite the established role of stress imaging and its increasing use in daily clinical practice, there are currently no specific guidelines, and little data are available in the literature on this topic. The aim of this review is to summarize the most recent evidence on pediatric stress imaging and its clinical application with a focus on the advantages and limitations of each imaging modality currently available.

Coronary Microvascular Dysfunction in Patients with Congenital Heart Disease

Congenital heart diseases represent a wide range of cardiac malformations. Medical and surgical advances have dramatically increased the survival of patients with congenital heart disease, leading to a continuously growing number of children, adolescents, and adults with congenital heart disease. Nevertheless, congenital heart disease patients have a worse prognosis compared to healthy individuals of similar age. There is substantial overlap in the pathophysiology of congenital heart disease and heart failure induced by other etiologies. Among the pathophysiological changes in heart failure, coronary microvascular dysfunction has recently emerged as a crucial modulator of disease initiation and progression. Similarly, coronary microvascular dysfunction could be important in the pathophysiology of congenital heart diseases as well. For this systematic review, studies on maximal vasodilatory capacity in the coronary microvascular bed in patients with congenital heart disease were searched using the PubMed database. To date, coronary microvascular dysfunction in congenital heart disease patients is incompletely understood because studies on this topic are rare and heterogeneous. The prevalence, extent, and pathophysiological relevance of coronary microvascular dysfunction in congenital heart diseases remain to be elucidated. Herein, we discuss what is currently known about coronary microvascular dysfunction in congenital heart disease and future directions.

Myocardial Perfusion in Hypoplastic Left Heart Syndrome

BACKGROUND

The status of the systemic right ventricular coronary microcirculation in hypoplastic left heart syndrome (HLHS) is largely unknown. It is presumed that the systemic right ventricle's coronary microcirculation exhibits unique pathophysiological characteristics of HLHS in Fontan circulation. The present study sought to quantify myocardial blood flow by cardiac magnetic resonance imaging and evaluate the determinants of microvascular coronary dysfunction and myocardial ischemia in HLHS.

METHODS

One hundred nineteen HLHS patients (median age, 4.80 years) and 34 healthy volunteers (median age, 5.50 years) underwent follow-up cardiac magnetic resonance imaging ≈1.8 years after total cavopulmonary connection. Right ventricle volumes and function, myocardial perfusion, diffuse fibrosis, and late gadolinium enhancement were assessed in 4 anatomic HLHS subtypes. Myocardial blood flow (MBF) was quantified at rest and during adenosine-induced hyperemia. Coronary conductance was estimated from MBF at rest and catheter-based measurements of mean aortic pressure (n=99).

RESULTS

Hyperemic MBF in the systemic ventricle was lower in HLHS compared with controls (1.89±0.57 versus 2.70±0.84 mL/g per min; P<0.001), while MBF at rest normalized by the rate-pressure product, was similar (1.25±0.36 versus 1.19±0.33; P=0.446). Independent risk factors for a reduced hyperemic MBF were an HLHS subtype with mitral stenosis and aortic atresia (P=0.017), late gadolinium enhancement (P=0.042), right ventricular diastolic dysfunction (P=0.005), and increasing age at total cavopulmonary connection (P=0.022). The coronary conductance correlated negatively with systemic blood oxygen saturation (r, -0.29; P=0.02). The frequency of late gadolinium enhancement increased with age at total cavopulmonary connection (P=0.014).

CONCLUSIONS

The coronary microcirculation of the systemic ventricle in young HLHS patients shows significant differences compared with controls. These hypothesis-generating findings on HLHS-specific risk factors for microvascular dysfunction suggest a potential benefit from early relief of frank cyanosis by total cavopulmonary connection.

Feasibility and Utility of Adenosine Stress Echocardiography in Children Following Post-Arterial Switch Operation: A Comparison with Technetium 99m-Sestamibi Myocardial Perfusion SPECT (MPS)

There is a need for a sensitive, safe, and cost-effective tool for coronary assessment among asymptomatic post-operative children who have undergone arterial switch operation (ASO) for transposition of great arteries (TGA). Adenosine stress echocardiography may be useful in assessing major structures as well for coronary functional assessment. Twenty-six children [median age 6.0 years; IQR 4.9-7.1 years, (22 boys)], who had undergone ASO at a median age of 40 days (IQR 30-75 days), were prospectively included. Left ventricular ejection fraction (LVEF) was calculated in both rest and stress studies (140 µg/kg/min of adenosine IV over 4 min), along with assessment of regional myocardial wall motion. Coronary flow reserve (CFR) was also measured in the left anterior descending artery (LAD). Technetium 99m-MIBI [0.2mCi/kg] was injected after 2 min of adenosine infusion. Adenosine infusion had to be stopped in two children, due to transient atrioventricular (AV) block. The LVEF increased from 55.87 ± 7.27 to 61.20 ± 7.70% (p  < 0.001) with adenosine stress. No significant regional wall motion abnormality was seen in rest or stress. Distal LAD could not be visualized in four patients. Basal and peak coronary flow velocities were 41.51 ± 14.12 and 74.18 ± 6.01 cm/s. Mean CFR was 1.91 ± 0.51. Myocardial perfusion scintigraphy (MPS) was normal in all the patients. Four patients were lost to follow-up and remaining children did not develop any adverse events in the follow-up period of 64.5 ± 7.19 months. Adenosine stress echocardiography is feasible as the initial screening test in the assessment of asymptomatic post-operative children with ASO, at minimal to no inconvenience to the patient. The findings concurred with stress MPS.

Pediatric Cardiac PET/CT Imaging

With the routine availability of PET/CT imaging for oncologic purposes, there has been renewed interest in and acceptance of cardiac and neurologic applications of PET/CT. As our understanding of the pathophysiology underlying various pediatric heart diseases has improved, there has been a parallel advance in imaging modalities. Cardiac MR imaging and cardiac PET continue to improve in the pediatric domain. Molecular imaging holds promise to provide a more robust assessment of the cardiac pathophysiology in a 1-stop setting with less radiation exposure to the patient, an important consideration for the pediatric patient population.

Evaluation of Left Ventricular Function Long Term After Arterial Switch Operation for Transposition of the Great Arteries

Long-term after arterial switch operation for transposition of the great arteries, abnormal coronary anatomy and altered loading conditions could compromise ventricular function. The current study investigates whether left ventricular function, measured with echocardiographic bi-plane ejection fraction and deformation imaging, in patients long term after arterial switch operation for transposition of the great arteries differs from healthy peers. A cross-sectional cohort study of patients at least 12 years after arterial switch operation was analyzed with bi-plane Simpson's left ventricular ejection fraction (LVEF) and deformation (speckle tracking) echocardiography. 81 patients, median age 20.6 (interquartile range 13.5-28.4) years, were included. LVEF was normal on average at 55.5 ± 6.1%. Global longitudinal strain (GLS) was lower in patients compared to healthy peers throughout all age groups and on pooled average (- 15.4 ± 1.1% vs. - 23.2 ± 0.9%). Although LVEF is normal on average in patients after arterial switch operation for transposition of the great arteries, GLS is impaired compared to healthy peers. The reduced GLS could indicate sub-clinical myocardial dysfunction.

Attenuation of Pulse Pressure Amplification in Patients with Complete Transposition of the Great Arteries After an Arterial Switch Operation in Children

Although the arterial switch operation has become the standard procedure for infants with complete transposition of the great arteries, possible late adverse events after surgery have not been fully elucidated. One such problem may be the postoperative function of the aorta that is radically manipulated. The current study enrolled 12 patients aged 4-9 years who had undergone an arterial switch operation. The ascending and descending aortic pressure waveforms were recorded by a catheter-mounted pressure sensor. The pressure values were compared with those of 28 age-matched controls. The mean patient age was 6.5 ± 1.0 years, and the mean age at the time of surgery was 15.2 ± 8.7 days. The pulse pressure in the ascending aorta was greater in the patients than in the controls (37.7 ± 5.7 vs. 33.5 ± 5.3 mmHg, p = 0.042), while no difference was observed at the descending aorta between the two groups (39.5 ± 5.1 vs. 37.4 ± 5.4 mmHg, respectively, p = 0.27). The pulse pressure amplification, defined as the pulse pressure in the descending aorta minus that in the ascending aorta, was significantly lower in patients who had undergone the arterial switch operation than in control patients (1.8 ± 1.6 vs. 4.0 ± 2.3 mmHg, p = 0.0052). The augmented pulse pressure in the ascending aorta and attenuated pulse pressure amplification observed in children treated with arterial switch surgery for complete transposition of the great arteries may implicate the procedure as a cause of future cardiovascular disease.

Peripheral Endothelial Function After Arterial Switch Operation for D-looped Transposition of the Great Arteries

Coronary artery re-implantation during arterial switch operation in patients with D-looped transposition of the great arteries (D-TGA) can alter coronary arterial flow and increase shear stress, leading to local endothelial dysfunction, although prior studies have conflicting results. Endothelial pulse amplitude testing can predict coronary endothelial dysfunction by peripheral arterial testing. This study tested if, compared to healthy controls, patients with D-TGA after arterial switch operation had peripheral endothelial dysfunction. Patient inclusion criteria were (1) D-TGA after neonatal arterial switch operation; (2) age 9-29 years; (3) absence of known cardiovascular risk factors such as hypertension, diabetes, hypercholesterolemia, vascular disease, recurrent vasovagal syncope, and coronary artery disease; and (4) ability to comply with overnight fasting. Exclusion criteria included (1) body mass index ≥85th percentile, (2) use of medications affecting vascular tone, or (3) acute illness. We assessed endothelial function by endothelial pulse amplitude testing and compared the results to our previously published data in healthy controls (n = 57). We tested 20 D-TGA patients (16.4 ± 4.8 years old) who have undergone arterial switch operation at a median age of 5 days (0-61 days). Endothelial pulse amplitude testing indices were similar between patients with D-TGA and controls (1.78 ± 0.61 vs. 1.73 ± 0.54, p = 0.73).In our study population of children and young adults, there was no evidence of peripheral endothelial dysfunction in patients with D-TGA who have undergone arterial switch operation. Our results support the theory that coronary arterial wall thickening and abnormal vasodilation reported in these patients is a localized phenomenon and not reflective of overall atherosclerotic burden.

Outcomes after Arterial Switch Operation for Simple Transposition

Without intervention, babies born with transposed great arteries (TGA) are doomed to a rapid death. Jatene and coworkers deserve the credit for performing the first successful arterial switch operation (ASO) in a patient with TGA and ventricular septal defect (VSD) in 1975. Since then ASO has become the procedure of choice in most medical centers. This review article summarizes the historical aspects of arterial switch operation and assesses this procedure's outcomes.

Clinical applications of radionuclide imaging in the evaluation and management of patients with congenital heart disease

Non-invasive testing of children with congenital heart disease (CHD) began in the 1950s with the introduction of radionuclide studies to assess shunt fractions, pulmonary blood flow, and ventricular contractile function. Echocardiography and cardiac magnetic resonance imaging have since replaced radionuclide imaging in many of these roles. Concurrently, percutaneous and surgical repairs of complex CHD evolved, creating new roles for radionuclide imaging. In this paper on applications of radionuclide imaging in CHD, we review the multiple mechanisms for myocardial ischemia in CHD. We critically compare optimal radionuclide imaging techniques to other imaging modalities for assessing ischemia in CHD. We present the current role of nuclear imaging for assessing viability and pulmonary blood flow. We highlight the value added by advances in dedicated cardiac SPECT scanners, novel reconstruction software, and cardiac PET in performing low-dose radionuclide imaging in CHD. Finally, we discuss the emerging clinical indications for radionuclide imaging in CHD including coronary flow reserve assessment and evaluation of cardiovascular prosthesis and device infections.

Anesthetic Considerations and Management of Transposition of the Great Arteries

Transposition of the great arteries was once an almost uniformly fatal disease in infancy. Six decades of advances in surgical techniques, intraoperative care, and perioperative management have led to at least 90% of patients reaching adulthood, most with a good quality of life. This review summarizes medical and surgical decision making during the neonatal perioperative period, with a special emphasis on factors pertinent to the anesthetic evaluation and care during primary surgical repair of transposition of the great arteries. A review is also provided of anesthetic considerations for noncardiac surgery later in childhood or adulthood, for those survivors of the arterial switch operation, Rastelli procedure, Nikaidoh procedure, and the réparation á l’étage ventriculaire procedure.

Coronary flow dynamics in children after repair of Tetralogy of Fallot

OBJECTIVES

To assess the possible effect of a stiff right ventricle on the coronary flow (CF) in patients with post-operative Tetralogy of Fallot (TOF).

BACKGROUND

Right ventricular restrictive physiology i.e. forward flow during atrial contraction (RVRP), is characteristic to many patients with post-operative TOF.

METHODS

A total of 34 patients with TOF anatomically corrected through transatrial repair were included. Coronary flow parameters were registered with transthoracic Doppler echocardiography from posterior descending (PDCA) and left anterior descending (LAD) coronary arteries in the same patient in 24/34 (71%) patients. Twenty age-matched healthy children were used as controls. Cardiac magnetic resonance (CMR) imaging was used to detect myocardial fibrosis, RV volume, and RVRP.

RESULTS

The mean age at investigation was 10.2 ± 2.8 years. RV end diastolic and end systolic volumes indexed for BSA were larger in patients with RVRP (p=0.002 and 0.008 respectively). Peak flow velocity in diastole and flow velocity time integral was increased in patients compared to controls. They were increased in the LAD in patients with fibrosis of RV (n=11) compared to patients without fibrosis (n=9) (p=0.01 and 0.047 respectively). LAD coronary flow was especially increased in patients with RVRP (n=9) as compared with those without (n=11), (p=0.006).

CONCLUSIONS

Patients at mid-term followup after correction of TOF show increase of coronary flow. This increase is more pronounced in patients with fibrosis and RVRP of the RV.

Adenosine stress myocardial perfusion scintigraphy in pediatric patients after arterial switch operation

Context:

Arterial switch operation (ASO) has become the established treatment for correction of transposition of great arteries (TGA). Despite the immediate correction of abnormal hemodynamics, acute and delayed complications related to the coronaries may cause morbidity and mortality.

Aims:

We evaluated the incidence of perfusion abnormalities and safety of adenosine by stress–rest myocardial perfusion single-photon emission computed tomography (SPECT) [myocardial perfusion scintigraphy (MPS)] using Tc-99m Sestamibi (MIBI) in asymptomatic children post-ASO.

Settings and Design:

Prospective study.

Materials and Methods:

We conducted a prospective, single-institutional study where stress–rest MPS was performed on 10 children of age between 1.25 and 6 years. Two of the patients had additional ventricular septal defect, one patient had left ventricular outflow tract obstruction, and another had Taussig–Bing anomaly. All the patients underwent corrective surgery as a single-stage procedure at the age of 176 ± 212 days (range 9-560 days). Adenosine was administered at a rate of 140 μg/kg/min intravenously as continuous infusion for duration of 6 min.

Statistical Analysis Used:

All the continuous variables were summarized as mean ± standard deviation, or range and median. Mann–Whitney test for unpaired data and Wilcoxon Rank test for paired samples were used.

Results:

The average increase in heart rate over the basal heart rate after adenosine stress was 59.7 ± 17.0%. No acute or remote complications were observed in any case. None of the patients demonstrated myocardial perfusion defects, either at rest or after adenosine stress.

Conclusions:

MPS post-adenosine induced vasodilatation is safe and feasible in patients of ASO for transposition of great arteries. One-stage repair, implantation of excised coronary buttons within neo-aortic sinus, and minimal or no mobilization of proximal coronaries may eliminate the occurrence of perfusion defects in patients of corrected TGA.

Twenty-eight years' experience of arterial switch operation for transposition of the great arteries in a single institution

OBJECTIVES

We reviewed our 28 years of experience of arterial switch operation (ASO) for transposition of the great arteries to investigate late sequelae of this procedure.

METHODS

387 patients who underwent ASO from 1984 to 2010 were included in this retrospective study. The longitudinal data were estimated by the Kaplan-Meier method and compared using a log-rank test. Risk factors for late sequelae were analysed by the multivariable Cox proportional hazards model.

RESULTS

The mean follow-up time was 10.0 years. There were 13 early deaths and 17 late deaths. All late deaths were within 1 year, except for three patients. Actuarial survival was 92.2 and 91.6% at 10 and 20 years, respectively. Sixty-six patients (17.1%) had developed pulmonary stenosis (PS) and 29 patients (7.5%) had developed moderate or more aortic insufficiency (AI) during follow-up. Selective coronary angiography was performed in 210 patients (54.3%) at 9.6 ± 5.1 years after ASO. Left main tract occlusion was found in 2 patients (2/210; 1.0%) and hypoplastic left coronary artery was found in 10 patients (10/210; 4.8%). Among these 12 patients, 8 patients were asymptomatic. Re-operation was performed in 76 patients (19.6%), pulmonary artery plasty for PS in 58 patients (15.0%), aortic valve replacement for AI including two Bentall operations in 9 patients (2.3%) and others. Freedom from re-operation was 78.2 and 62.8% at 10 and 20 years, respectively. The risk factor for PS was the use of equine pericardium for reconstruction (P < 0.0001). Factors associated with moderate or more AI was the presence of left ventricular outflow tract obstruction (P = 0.004). There were no risk factors for late coronary lesions. Three hundred and forty surviving patients (340/357; 95.2%) were in NYHA functional class I. Treadmill test, which was performed on 217 patients (56.1%) at 14.3 ± 5.4 years after ASO, revealed that the maximum heart rate was 97.5 ± 7.6% of normal and peak oxygen consumption was 105.2 ± 20.5% of normal.

CONCLUSIONS

ASO was performed with satisfactory results in the overall survival and functional status. PS was the main reason for re-operation. Coronary lesions can appear late without any symptoms. Benefits of ASO can be achieved by long-term follow-ups of PS, AI and coronary lesions.

Cardiac outcomes in young adult survivors of the arterial switch operation for transposition of the great arteries

OBJECTIVES

We sought to determine cardiac outcomes in young adults with complete transposition of the great arteries (TGA) after the arterial switch operation (ASO).

BACKGROUND

Although cardiac outcomes in the pediatric population with TGA after ASO have been well described, outcomes in the adult population have not to our knowledge been studied.

METHODS

We determined late survival in all operative survivors with TGA after ASO performed before 1991 at our local pediatric referring hospital. In the subset of adults (n = 65) followed in our adult congenital cardiac clinic, we examined cardiac outcomes in adulthood.

RESULTS

Survival of the 132 infants discharged from hospital after ASO was 97% (70% confidence interval [CI]: 95.0% to 98.1%) at 20 years. In the 65 patients (mean age 21 +/- 3 years, 62% male) followed at our institution, 17% (11 of 65) had at least 1 clinically significant cardiac lesion, including ventricular dysfunction, valvular dysfunction, or arrhythmias. Residual lesions were more common in those who had had cardiac reinterventions in childhood (odds ratio: 10.7, 95% CI: 2.1 to 55). In adulthood, 5 patients (8%) had arrhythmia requiring treatment and 7 patients (11%) required reinterventions (5 reoperations and 2 pacemaker implantations). Intervention for aortic valve regurgitation and aortic root dilation were not observed. Exercise capacity was reduced in most adults (82%) after ASO.

CONCLUSIONS

Although most adults after ASO are well, and few have residual defects, there are subgroups, particularly those who needed further cardiac intervention in childhood, who are at higher risk for ventricular and valve dysfunction and arrhythmias.

Myocardial perfusion magnetic resonance imaging for detecting coronary function anomalies in asymptomatic paediatric patients with a previous arterial switch operation for the transposition of great arteries

BACKGROUND

The main cause of long-term morbidity and mortality after the arterial switch operation for transposition of great arteries is complication at the coronary arteries. Myocardial perfusion magnetic resonance imaging represents a relatively novel and appealing tool for detecting myocardial ischaemia but with little experience in paediatric patients. The purpose of this paper is to report a single centre experience with myocardial perfusion magnetic resonance imaging for detecting ischaemia after the arterial switch operation for transposition of great arteries.

METHODS

Twenty-eight patients aged 13-16 years with an arterial switch operation for transposition of great arteries were included in the study. Coronary pattern, operative and postoperative complications, and long-term follow-up events were reviewed. Patient functional evaluation included clinical examination, electrocardiogram and echocardiogram. Every patient underwent magnetic resonance imaging perfusion scanning at rest and under adenosine-induced stress.

RESULTS

All patients were symptom free with no ischaemic signs on the electrocardiogram. All magnetic resonance imaging examinations were generally well tolerated with minor adenosine secondary effects in 36% of the patients. Two stress myocardial perfusion magnetic resonance studies were excluded from analysis for technical reasons. No perfusion stress defects were detected at the remaining 26. Myocardial delayed enhancement was performed in all 28 patients. In five subjects, a subendocardial late enhancement consistent with patch tissue for septal defect closure at the time of repair was indentified.

CONCLUSION

Magnetic resonance imaging evaluation of myocardial perfusion and viability is feasible in paediatric patients long after arterial switch operation. No signs of myocardial ischaemia or necrosis were documented in this young asymptomatic population. Further studies including coronary angiography correlation are needed to validate magnetic resonance imaging results.

Coronary diameter and vasodilator function in children following arterial switch operation for complete transposition of the great arteries

Coronary reimplantation during arterial switch operation (ASO) may affect coronary artery growth and function during childhood. The purpose of this study was to assess coronary artery diameter and regional myocardial blood flow (MBF) and myocardial flow reserve (MFR) in children after neonatal ASO. We measured proximal diameters of left anterior descending (LAD), left circumflex, and posterior descending coronary arteries on coronary angiogram in 12 children (median age 11 years, range 7.6 to 15.1) with a history of neonatal ASO. These children then underwent cardiac positron emission tomographic imaging using nitrogen-13 ammonia to assess MBF at baseline and during intravenous adenosine hyperemia in regions supplied by these 3 coronary arteries. Coronary artery z-scores were within normal range (-2.0 to 2.0) for 32 of 36 coronary arteries. MFR (ratio of hyperemic to basal MBF) was normal (>2.5) in all myocardial regions in 10 of 12 patients. The remaining 2 patients, 1 with a dual LAD and 1 with LAD origin from the right coronary artery, had generalized impairment of hyperemic MBF (<2.0 ml/g/min) and low MFR (<2.5). Coronary artery z-scores and MFR in corresponding myocardial territories were not correlated (r = 0.15, p = 0.36). In conclusion, coronary growth and function appear to be normal in most children after neonatal ASO. Children with anatomic LAD abnormalities may be at increased risk of impaired MFR.

A study of the physiological consequences of sympathetic denervation of the heart caused by the arterial switch procedure

BACKGROUND

The arterial switch operation is the corrective operation for transposition of the great arteries, defined as the combination of concordant atrioventricular and discordant ventriculo-arterial connections, but there have been concerns about silent subendocardial ischaemia on exercise and coronary artery growth. The arterial switch divides the majority of the sympathetic nerves entering the heart; we have studied the effects of coronary flow and sensitivity to catecholamine stimulation in an animal model.

METHODS

A total of 10 piglets were operated on cardiopulmonary bypass with section and resuturing of aortic trunk, pulmonary artery and both coronary arteries, with 13 sham-operated controls. After 5-7 weeks of recovery, seven simulated switch survivors and 13 controls were studied.

RESULTS

Basal heart rate was significantly higher in switch piglets: in vivo mean (standard deviation) 112 (12) versus sham 100 (10) beats per minute, (p = 0.042); in vitro (Langendorff preparation): 89 (9) versus sham 73 (8) beats per minute (p = 0.0056). In vivo maximal heart rate in response to epinephrine was increased in switch piglets, 209 (13) versus 190 (17) beats per minute (p = 0.044). In vitro dose-response curves to norepinephrine were shifted leftward and upwards (p = 0.0014), with an 80% increase in heart rate induced by 0.095 (0.053) norepinephrine micromole per litre perfusate in switch hearts versus 0.180 (0.035) norepinephrine micromole per litre (p = 0.023). Increase in coronary flow on norepinephrine stimulation and maximal coronary flow were significantly reduced in switch hearts: 0.3 (0.2) versus 0.8 (0.4) millilitre per gram heart weight (p = 0.045) and 2.5 (0.4) versus 3.1 (0.4) millilitre per gram heart (p = 0.030), respectively.

CONCLUSIONS

A combination of increased intrinsic heart rate, increased sensitivity to chronotropic actions of norepinephrine, and a decreased maximal coronary flow creates potential for a mismatch between perfusion and energy demands.

Long-term outcomes after an arterial switch operation for simple complete transposition of the great arteries

BACKGROUND AND OBJECTIVES

Although coronary artery obstruction, aortic insufficiency (AI), and pulmonary stenosis (PS) have been reported after arterial switch operation (ASO), limited long-term studies on ASO exist. Our study aimed to examine long-term outcomes after ASO for simple complete transposition of the great arteries (TGA).

SUBJECTS AND METHODS

All 108 patients with simple complete TGA who underwent ASO at Seoul National University Children's Hospital between 1987 and 2004 were enrolled. We retrospectively reviewed the patients' medical records and the results of various functional and imaging studies.

RESULTS

Among 108 cases of ASO for simple TGA, 96 have been followed-up through the present time (mean follow-up duration was 11.7+/-8.6 years: range= 4 to 23 years). The 20-year rates of freedom from significant AI, PS, and coronary obstruction were 78.6%, 67.8%, and 95.8%, respectively. AI showed a tendency to progress as follow-up time increased in 21.4% of the population studied (p=0.014); however, AS, PS, and PI showed no such progression. Late coronary artery occlusion was not associated with the initial coronary arterial pattern. Re-operations were done for 13 patients (13.5%) at an average of 8+/-4.3 years after ASO. The survival rate was 96%, while the re-operation-free was 90% at 10 years and 83% at 20 years. Most patients showed normal physical growth with good activity {98%; New York Heart Association (NYHA) class 1 activity} and normal development (96%).

CONCLUSION

Although most patients showed normal physical growth and development after successful ASO, meticulous long-term follow-up is necessary because of progressive AI and coronary complications.

Stress imaging in congenital cardiac disease

In patients with coronary arterial disease, stress imaging is able to demonstrate abnormalities in the motion of the ventricular walls, and abnormalities in coronary arterial perfusion not apparent at rest. It can also provide information on prognostic factors. In patients with congenitally malformed hearts, stress imaging is used to determine contractile reserve, abnormalities of mural motion, and global systolic function, but also to assess diastolic and vascular function. In most of these patients, stress is usually induced using pharmacological agents, mainly dobutamine given in varying doses. The clinical usefulness of abnormal responses to the stress induced in such patients has to be addressed in follow-up studies. The abnormal stress might serve as surrogate endpoints, predicting primary endpoints at an early stage, which are useful for stratification of risk in this population of growing patients. We review here the stress imaging studies performed to date in patients with congenitally malformed hearts, with a special emphasis on echocardiography and cardiac magnetic resonance imaging.

Determinants of exercise capacity after arterial switch operation for transposition of the great arteries

Patients who undergo the arterial switch operation for transposition of the great arteries (TGA) are at risk of reduced exercise capacity, with most reports focusing on chronotropic incompetence as the cause. Residual right ventricular outflow tract (RVOT) obstruction is relatively common after the arterial switch operation, but its effect on exercise capacity is unknown. We studied 60 patients (44 males, age 13.3 +/- 3.4 years) who had undergone a neonatal arterial switch operation using the cardiopulmonary exercise test and transthoracic echocardiography. The peak exercise oxygen uptake (VO(2)), and heart rate were recorded and are expressed as the percentage of predicted values. The greatest velocity detected by echocardiography across the pulmonary valve, pulmonary trunk, or pulmonary branches was used in the analysis as an index of RVOT obstruction. The peak VO(2)% was 84 +/- 15%, and the peak heart rate percentage was 97 +/- 8%. Of the 60 patients, 29 had an abnormal peak VO(2)% (< or =84%) and 3 (5%) had an abnormal peak heart rate percentage (< or =85%). The maximal RVOT velocity was 2.3 +/- 0.6 m/s, and it correlated with the peak VO(2)% (r = -0.392, p = 0.004). On multivariate analysis, the presence of residual RVOT obstruction (p = 0.0007) was the only variable associated with a reduced peak VO(2)%. Patients with a RVOT maximal velocity > or =2.5 m/s had a lower peak VO(2)% than those with lower velocities (p <0.0001). No relation was found between age at testing and the peak VO(2)%. In conclusion, a reduced exercise capacity is relatively common in children and young adults who have undergone an arterial switch operation, but it does not decrease with age. The presence of residual RVOT obstruction seems to have an effect on exercise capacity.

Aortic reservoir function after arterial switch operation in elementary school-aged children

BACKGROUND

After the arterial switch procedure, decreased distensibility of the aortic root has been reported, which means impaired aortic reservoir function of the coronary circulation, but there have been no reports regarding the relationship of this issue to myocardial perfusion. Therefore, in the present study the aortic reservoir function and coronary supply-demand balance were examined in patients after undergoing the arterial switch operation (ASO) around the time of entering elementary school.

METHODS AND RESULTS

Diastolic runoff (DR), which is the percentage of diastolic blood flow to total cardiac output, was measured as the index of aortic reservoir function. The subendocardial viability ratio was investigated as the index of coronary supply - demand balance. In the patient group, the aortic root was dilated (p<0.0001) and distensibility was impaired (p<0.0001) in comparison with an age-matched control group. However, there was no difference between the 2 groups in DR or subendocardial viability ratio.

CONCLUSIONS

Coronary supply - demand balance was preserved in the pediatric ASO patients, despite the aortic root dysfunction. The preserved DR suggests that dilatation of the aorta compensates for aortic reservoir function. Because large artery dysfunction predicts future cardiovascular diseases, careful follow-up is crucial.

Intraoperative coronary artery pulse Doppler patterns in patients with complete transposition of the great arteries undergoing the arterial switch operation

BACKGROUND

Arterial switch operation is standard repair for complete transposition of the great arteries (TGA). Coronary artery abnormalities are the most common cause of morbidity and mortality in the acute postoperative phase. This study was designed to determine whether coronary artery pulse Doppler flow patterns obtained by transesophageal echocardiography during the arterial switch operation are correlated with acute postoperative outcomes.

METHODS

A retrospective review of all patients with TGA undergoing the arterial switch operation between 2004 and 2006 was performed. Intraoperative coronary artery pulse Doppler flow patterns were analyzed by 2 blinded investigators. Associations of coronary artery pulse Doppler flow patterns with clinical outcomes were sought using multivariable linear and logistic regression analysis.

RESULTS

Sixty-three patients (48 male, gestational age 38 +/- 2 weeks, birth weight 3,514 +/- 613 g) were analyzed. Three patients needed mechanical support (2 died), 19 had delayed sternal closure, 17 had arrhythmias, and 9 had ST changes. The most common coronary artery pulse Doppler flow pattern consisted of a late systolic peak followed by low-velocity flow throughout diastole. A left main coronary artery (LMCA) velocity time integral >0.14 (P = .01) and an LMCA peak systolic velocity >0.6 cm/s (P = .05) were associated with need for surgical revision.

CONCLUSION

Abnormalities in LMCA flow were associated with the need for surgical revision in patients with TGA undergoing the arterial switch operation. Normal coronary artery pulse Doppler flow patterns after the arterial switch operation consisted of a late systolic peak followed by low-velocity flow throughout diastole.

Preliminary data on the diagnostic accuracy of rubidium-82 cardiac PET perfusion imaging for the evaluation of ischemia in a pediatric population

Evaluation of myocardial perfusion is sometimes necessary in children with congenital heart disease or acquired coronary artery abnormalities. Limited information is available regarding the clinical utility of myocardial perfusion imaging in children. PET imaging with rubidium-82 may provide a convenient clinical means of assessing regional circulatory compromise in pediatric patients with small hearts, due to its improved spatial resolution. Clinically indicated cardiac PET studies obtained in 22 pediatric patients were reviewed by two blinded observers and assigned myocardial perfusion scores using a standard 17-segment model. PET results were correlated with coronary angiography, available in 15 cases, to determine the accuracy of PET scanning for evaluating compromise of the myocardial circulation. Reversible defects consistent with myocardial ischemia were present in 6 of 15 (40%) PET cases. The sensitivity and specificity of cardiac PET for the detection of significant coronary artery disease were 100% and 82%, respectively. The positive predictive value of cardiac PET was 67%, while the negative predictive value was 100%. Cardiac PET imaging with rubidium-82 appears promising for the noninvasive assessment of myocardial perfusion in the pediatric population. The findings from this small series suggest that prospective study in a larger patient cohort merits consideration.

Coronary artery pattern and age impact exercise performance late after the arterial switch operation

OBJECTIVE

The impact of coronary artery pattern on exercise performance after the arterial switch operation is unknown. The purpose of this study was to evaluate the relationship between coronary artery pattern and exercise performance late after the arterial switch operation.

METHODS

Patients who underwent the arterial switch operation and were referred for exercise stress testing between January of 1996 and April of 2005 were included. Univariate and multivariate analyses were performed to identify risk factors for lower maximum heart rate and percent of predicted peak oxygen consumption.

RESULTS

Fifty-three patients were included; 72% were male. The median age at the arterial switch operation was 5 days (1 day to 3.6 years); 32% had concurrent ventricular septal defect repair. The time from the arterial switch operation to exercise stress testing was 14.1 years (7.7-20.6 years). There were 37 patients with the usual coronary artery pattern, and 16 patients (30%) with variant coronary artery patterns. At exercise stress testing, there was no difference in respiratory exchange ratio (1.16 +/- 0.1 for both), indicating similar effort. Compared with patients with the usual coronary artery pattern, patients with variant coronary artery patterns had a significantly lower maximum heart rate (177 +/- 16 beats/min [89% predicted] vs 186 +/- 11 beats/min [93% predicted], respectively, P = .04). Percent of predicted peak oxygen consumption was not significantly different between patients with the usual coronary pattern and patients with variant coronary artery patterns (89% +/- 20% vs 80% +/- 17%, respectively, P = .12). In multivariate analysis, variant coronary artery patterns (P = .03) and ventricular septal defect (P = .004) were predictors of significantly lower maximum heart rate and were associated with a trend toward lower percent of predicted peak oxygen consumption (P < .09). Longer follow-up time was the strongest predictor of lower percent of predicted peak oxygen consumption (P < .001).

CONCLUSIONS

Variant coronary artery patterns are associated with chronotropic impairment, and longer follow-up time is the strongest predictor of diminished aerobic capacity late after arterial switch operation.

Obesity is a common comorbidity in children with congenital and acquired heart disease

OBJECTIVES

Obesity may pose additional cardiovascular risk to children with acquired and congenital heart disease. Many children with heart disease are sedentary as a result of physician-, parent-, and/or self-imposed restrictions. The aim of this study was to evaluate the impact of the epidemic of obesity on children with heart disease.

PATIENTS AND METHODS

A cross-sectional review was performed of children evaluated in 2004 at 2 cardiology outpatient clinics. Differences in the prevalence of obese (BMI > or = 95%) and overweight (BMI 85%-95%) children were compared with national data and healthy control subjects. Dictated letters were reviewed to determine whether obesity was discussed with referring practitioners.

RESULTS

Of 2921 patients assessed, 1523 had heart disease. Diagnostic subgroups included "mild" heart disease (n = 401), arrhythmia (n = 447), biventricular repair (n = 511), univentricular palliation (Fontan; n = 108), and heart transplantation (n = 56). More than 25% of the patients with heart disease were obese or overweight; the prevalence of obese and overweight children was significantly lower only in the Fontan group (15.9%). Pediatric cardiologists failed to document obesity or weight counseling in the majority of clinic letters.

CONCLUSIONS

Obesity is common in children with congenital and acquired heart disease. Pediatric cardiologists demonstrate inadequate communication regarding this problem to referring practitioners. Healthy-lifestyle counseling and routine exercise in children with heart disease may be underemphasized.

Exercise Intolerance in Adults with Congenital Heart Disease

This article describes the ways to assess exercise capacity in adults with congenital heart disease (ACHD) and the impact of exercise intolerance in the population. It also discusses the likely pathogenesis of exercise intolerance in ACHD, the similarities between ACHD and acquired heart failure, and potential therapeutic options.

Is the arterial switch operation as good over the long term as we thought it would be?

Surgical intervention for hearts with transposition, defined as concordant atrioventricular and discordant ventriculo-arterial connections, has been one of the landmark achievements in the field of paediatric cardiac surgery. In the early 1950s, pioneer surgeons attempted to palliate patients with transposed arterial trunks with an early form of the arterial switch operation. As a result of initially dismal outcomes secondary to difficulties with coronary arterial transfer, the unprepared nature of the morphologically left ventricle, and primitive methods for cardiopulmonary bypass, the arterial switch was abandoned in favour of several procedures achieving correction at atrial and venous levels, culminating in the Mustard and Senning operations.1,2These innovative procedures produced the earliest surviving children with transposition. Although the atrial switch procedures achieved widespread acceptance and success during the mid-1960s through the mid-1980s, the search for an operation to return the great arteries to their normal anatomic positions continued. This pursuit was stimulated primarily by the accumulating observations in mid-to-late term follow up studies of: an increasing frequency of important arrhythmic complications, including sinus nodal dysfunction, atrial arrhythmias, and sudden, unexplained death, by the development of late right ventricular dysfunction and significant tricuspid regurgitation in a ventricle potentially unsuited for a lifetime of systemic function by a small but important prevalence of obstruction of the systemic and/or pulmonary venous pathways, and by dissatisfaction with the operative mortality in the subgroup of infants complicated by additional presence of a large ventricular septal defect.3–6As we have already discussed, a number of novel procedures to achieve anatomic correction had been described as early as 1954, but clinical success was not accomplished until 1975, when Jatene and co-workers7astounded the world of paediatric cardiology with their initial description.

Myocardial scars determined by delayed-enhancement magnetic resonance imaging and positron emission tomography are not common in right ventricles with systemic function in long-term follow up

OBJECTIVE

To test the hypothesis that myocardial scars are common in patients with systemic right ventricles.

METHODS

27 consecutive patients with systemic right ventricle were studied with delayed-enhancement magnetic resonance imaging and positron emission tomography. Of the 27 patients, 18 had had an atrial switch operation a mean of 21.8 (SD 4.5) years previously and were 23.4 (SD 5.3) years old. Nine patients without previous heart surgery had congenitally corrected transposition of the great arteries and were 35.3 (SD 15.6) years old.

RESULTS

Only one patient had a subendocardial scar identified by delayed-enhancement magnetic resonance imaging. Positron emission tomography identified no myocardial scars.

CONCLUSIONS

This study shows that the hypothesis that myocardial scars are common in patients with systemic right ventricles is not correct.

Abnormal Vasomotor Function of the Epicardial Coronary Arteries in Children Five to Eight Years After Arterial Switch Operation

OBJECTIVES

This study sought to test the vasoreactivity of the translocated coronary arteries after arterial switch operation (ASO) using quantitative angiographic analysis and intracoronary Doppler flow wire velocimetry.

BACKGROUND

Late coronary artery events occur in 3% to 8% of patients after the ASO. Previous studies of coronary flow reserve have yielded disparate results.

METHODS

Nineteen children previously underwent ASO (13 boys, age 5.4 +/- 3.2 years, weight 22.3 +/- 10.6 kg), and six control patients were enrolled in the study. Each patient underwent quantitative angiographic assessment of the epicardial coronary arteries before and after administration of nitroglycerin and coronary blood flow volume assessment before and after administration of adenosine and acetylcholine. The results were compared between groups.

RESULTS

Epicardial coronary artery dilation in response to intracoronary nitroglycerin was significantly less in the ASO group than in the control group (left anterior descending [LAD], 5.0 +/- 0.05% vs. 18.0 +/- 4.5%, p = 0.0009; right coronary artery [RCA], 4.0 +/- 0.07% vs. 32.7 +/- 12.7%, p = 0.006). Moreover, the coronary blood flow volume reserve was reduced in ASO patients compared with control patients after intracoronary infusion of acetylcholine (2.3 +/- 0.9 vs. 4.9 +/- 1.7, p = 0.0003) or adenosine (2.7 +/- 1.5 vs. 5 +/- 0.5, p = 0.002).

CONCLUSIONS

Epicardial coronary arteries fail to dilate normally in children after ASO, and the calculated coronary flow volume reserve is consequently reduced.

Assessment of left ventricular function long term after arterial switch operation for transposition of the great arteries by dobutamine stress echocardiography

OBJECTIVES

To use dobutamine stress echocardiography to determine left ventricular (LV) function and wall motion of children long term after arterial switch operation (ASO) for transposition of the great arteries.

DESIGN AND PATIENTS

31 patients (24 boys) with ASO performed at a mean (SD) of 15.5 (4.3) days of life were studied at an age of 9.4 (2.0) years. All had normal coronary angiographic findings. LV echocardiographic indexes, including fractional shortening, ejection fraction, rate corrected velocity of circumferential fibre shortening (VCFc), and wall stress, as well as LV wall motion abnormalities were determined at rest and under dobutamine stress. The results were compared with those of 20 healthy age matched control participants.

SETTING

Tertiary paediatric cardiac centre.

RESULTS

Fractional shortening, ejection fraction, and VCFc were significantly lower in patients than in controls at rest (all with p < 0.001). Stress-velocity index detected impaired LV contractility in 19 (61%) patients at rest. An older age at operation (p = 0.01), longer bypass (p = 0.01) and circulatory arrest times (p = 0.045), and an unusual coronary artery pattern (p = 0.059) were associated with impaired resting LV contractility. Dobutamine stress echocardiography unmasked wall motion abnormalities in 23 (74%) patients. Exercise myocardial perfusion scan, performed in 22 patients, showed reversible myocardial perfusion defects in 17. These defects corresponded to segments of hypokinesia as detected by dobutamine stress echocardiography.

CONCLUSION

A significant proportion of children, albeit asymptomatic, had impaired baseline LV contractility and reversible myocardial perfusion defects and mild wall motion abnormalities on stress after ASO.

Posterior descending coronary artery flow reserve assessment by Doppler echocardiography in children with and without congenital heart defect: comparison with invasive technique

To evaluate whether transthoracic Doppler echocardiography can reliably measure coronary flow velocity and coronary flow velocity reserve (CFVR) in the posterior descending coronary artery (PD) in children, we examined 32 patients who had congenital heart disease (ventricular septal defect in 10, tetralogy of Fallot in 6, tricuspid atresia in 3, double-outlet right ventricle in 2, patent ductus arteriosus in 2, and aortic valve stenosis in 2) and 7 patients who had a history of Kawasaki disease without stenosis or aneurysm formation of the coronary artery. Average peak flow velocity (APV) in the PD was measured by transthoracic Doppler echocardiography at the time of intracoronary Doppler study. CFVR was defined as the ratio of hyperemic to basal APV. Clear envelopes of basal and hyperemic APV in the PD were obtained in 23 of 32 patients by transthoracic Doppler echocardiography. APV obtained from transthoracic Doppler echocardiography correlated highly with that from the Doppler guidewire method (r=0.91). The mean difference between transthoracic Doppler echocardiography and the Doppler guidewire method was 0.1+/-2.9. There was an excellent correlation between transthoracic Doppler echocardiography and the Doppler guidewire method for the measurements of CFVR (r=0.84). The mean difference between transthoracic Doppler echocardiography and Doppler guidewire was -0.016+/-0.198. Noninvasive measurement of coronary flow velocity and CFVR in the PD using transthoracic Doppler echocardiography accurately reflects invasive measurement of coronary flow velocity and CFVR by the Doppler guidewire method in pediatric patients with various heart diseases.

Coronary flow velocity and coronary flow velocity reserve in children with ventricular septal defect

To assess coronary flow characteristics in congenital heart defect with left ventricular (LV) volume overload, we examined 24 children (mean 12.1 +/- 7.1 months) with ventricular septal defect. The pulmonary to systemic flow ratio ranged from 1.1 to 3.0. Control group consisted of 10 age-matched children who had a history of Kawasaki disease with angiographically normal coronary artery in the acute phase. LV end-diastolic volume and LV mass were measured by left ventriculogram. With Doppler flow guide wire (0.014-inch), average peak flow velocity (APV) in left anterior descending coronary artery was recorded at rest and during hyperemia (0.16 mg/kg/min adenosine infusion intravenously). Coronary flow velocity reserve (CFVR) was calculated as the ratio of hyperemic/baseline APV. Seven patients were also studied 5-7 months after surgery. Compared with control subjects, CFVR was significantly reduced in patients with LVvolume overload (1.78 +/- 0.24 vs. 2.66 +/- 0.42, p < .0001) because baseline APV was significantly greater (30 +/- 8 vs. 23 +/- 5 cm/sec, p = 0.0027). Significant correlations were observed between CFVR and Qp/Qs, baseline APV, LV end-diastolic volume, or LVmass. Stepwise regression analysis showed that baseline APV and Qp/Qs were important determinants of CFVR (CFVR = 2.64-0.202 [Qp/Qs]-0.015 [APV] r = 0.83, p < 0.0001). In 7 patients with LVvolume overload, CFVR improved significantly after surgery because of reduction of baseline APV. CFVR is limited in patients with LV volume overload because of the elevation of baseline resting APV. LAD flow pattern is dependent on LV volume overload level and its changes after surgery.

Magnetic resonance imaging evaluation of myocardial perfusion and viability in congenital and acquired pediatric heart disease

This study examined the feasibility and potential clinical utility of magnetic resonance imaging (MRI) evaluation of myocardial perfusion (first-pass contrast enhancement) and viability (myocardial delayed enhancement) in 30 patients with congenital and acquired pediatric heart disease. Good agreement was found between MRI evaluation of myocardial perfusion and viability and analysis of segmental wall motion as well as coronary angiography (n = 10) and single photon emission computed tomography (n = 6).

Coronary flow reserve in the newborn lamb: an intracoronary Doppler guide wire study

Recent studies indicate a severely reduced coronary flow reserve (CFR) in neonates with congenital heart disease. The significance of these studies remains debatable, as the ability of the anatomically normal neonatal heart to increase coronary flow is currently unknown. This study was designed to establish normal values for CFR in newborns after administration of adenosine [pharmacologic CFR (pCFR)] and as induced by acute hypoxemia (reactive CFR). Thirteen mechanically ventilated newborn lambs were studied. Coronary flow velocities were measured in the proximal left anterior descending coronary artery before and after adenosine injection (140 and 280 microg/kg i.v.) using an intracoronary 0.014-in Doppler flow-wire. Measurements were made at normal oxygen saturation (SaO(2)) and during progressive hypoxemia induced by lowering the fraction of inspired oxygen. CFR was defined as the ratio of hyperemic to basal average peak flow velocity. In a hemodynamically stable situation with normal SaO(2), pCFR was 3.0 +/- 0.5. pCFR decreased with increasing hypoxemia. Regression analysis showed a linear relation between SaO(2) and pCFR (R = 0.86, p < 0.0001). Reactive CFR obtained at severe hypoxemia (Sao(2) <30%) was 4.2 +/- 0.8, and no significant further increase in coronary flow velocity occurred by administration of adenosine. Newborn lambs have a similar capacity to increase coronary flow in response to both pharmacologic and reactive stimuli as older subjects. Administration of adenosine does not reveal the full capacity of the newborn coronary circulation to increase flow, however, as the flow increase caused by severe hypoxemia is significantly more pronounced.

Coronary flow reserve assessment by Doppler echocardiography in children with and without congenital heart defect: comparison with invasive technique

To evaluate whether transthoracic Doppler echocardiography can reliably measure coronary flow velocity (CFV) and CFV reserve (CFVR) in the left anterior descending coronary artery (LAD) in children, we examined 12 patients who had a history of Kawasaki disease without stenosis or aneurysm formation of coronary artery and 9 patients who had congenital heart disease (ventricular septal defect in 6, patent ductus arteriosus in 2, tricuspid atresia in 1). The pulmonary-to-systemic flow ratio ranged from 1.7 to 2.8. CFV in the proximal LAD was measured by transthoracic Doppler echocardiography at the time of Doppler guidewire examination. CFV in the proximal LAD was measured at baseline and hyperemic conditions by both transthoracic Doppler echocardiography and Doppler guidewire techniques. CFVR was defined as "the ratio of peak hyperemic to basal CFV in the proximal LAD." Clear envelopes of basal and hyperemic CFV in the proximal LAD were obtained in 19 of 21 patients by transthoracic Doppler echocardiography. There was a significant correlation between transthoracic Doppler echocardiography and Doppler guidewire methods for the measurements of CFV (r = 0.84, P <.0001). The mean difference between the 2 methods was -0.5 +/- 5.9 cm/s. CFVR from transthoracic Doppler echocardiography correlated well with that from Doppler guidewire examinations (r = 0.83, P <.0001). The mean difference between the 2 methods was 0.06 +/- 0.24. Noninvasive measurement of CFV and CFVR in the proximal LAD using transthoracic Doppler echocardiography accurately reflects invasive measurement of CFV and CFVR by Doppler guidewire method in pediatric patients with various heart diseases.