Pediatric Cardiology

Dobutamine stress cardiac MRI is safe and feasible in pediatric patients with anomalous aortic origin of a coronary artery (AAOCA). Doan TT, Molossi S, Sachdeva S, Wilkinson JC, Loar RW, Weigand JD, Schlingmann TR, Reaves-O'Neal DL, Pednekar AS, Masand P, Noel CV.Int J Cardiol. 2021 Apr 20:S0167-5273(21)00667-7. doi: 10.1016/j.ijcard.2021.04.031. Online ahead of print.PMID: 33892043 Take home points: Dobutamine stress cardiac MRI (DSCMR) is feasible and safe in pediatric patients with AAOCA, with very low risk of major or minor adverse events Inducible hypoperfusion was present in a small percentage of patients, along with wall motion abnormalities, suggesting that detection of myocardial ischemia with this modality may be helpful in the management of these patients Commentary from Dr. Jared Hershenson (Greater Washington DC), section editor of Pediatric Cardiology Journal Watch:  Testing to reliably risk stratify patients with AAOCA has not yet been fully elucidated. It is well known that exercise stress testing, stress echo and nuclear perfusion imaging have a low negative predictive valve in detecting myocardial ischemia. This is especially true in patients with anomalous origin of the right coronary artery (AAORCA). This single center study from Texas Children’s Hospital prospectively enrolled all patients < 20 years old with AAOCA. DSCMR and dobutamine administration was performed via the following protocol showed in Figure 1. First pass imaging was added to the protocol due to previous research studies showing reversible ischemia preceding wall motion abnormalities. Dobutamine increases heart rate and contractility, decreases systemic vascular resistance and increases coronary vasodilation which makes it a useful agent to increase oxygen consumption. Atropine was added to achieve the target HR of at least 150 bpm. They also targeted a calculated rate pressure product (RPP) of greater than 20x10^3 bpm*mmHg, which was considered an indirect estimate of high intermediate myocardial oxygen consumption. Inducible hypoperfusion predicts adverse outcomes in adults with ischemic heart disease, so this study was done to assess the feasibility and safety in the pediatric population and to help decision making with their cohort (eg. surgery vs. observation). 221 DSCMRs were completed on 182 patients. 14% had AAOLCA, 9% had intraseptal AAOLCA, and 77% had AAORCA.  Maximum dobutamine dose of 40 mcg/kg/min was given in 94% of studies, and atropine was given in 63%. Sedation was provided in 17% of patients primarily due to younger age. 86% achieved the target RPP. Heart rate did not affect first pass perfusion image quality and only HR > 85% age-predicted maximum reduced cine image quality, which was still adequate in all patients. Intraobserver agreement was very good. No major events (ventricular arrhythmia, MI, cardiac arrest) occurred, and 12.5% had minor events (severe HTN, chest pain, nausea/vomiting, paradoxical bradycardia, rash, anxiety, dizziness, or dyspnea) with none associated with sedation.   Inducible hypoperfusion was detected in 31/221, with 13/31 having wall motion abnormalities. See Table 2. Of the 161 first time DSCMR, 80% had AAORCA, 10% AAOLCA, and 10% intraseptal AAOLCA. Symptoms of exertional chest pain or exertional syncope were associated with inducible hypoperfusion. 13% of AAORCA, 18% AAOLCA, and 44% intraseptal had inducible hypoperfusion (total 27/161). 70% of those underwent successful surgical intervention, 15% were pending, and 15% were medically managed. Post-surgery, only 1 had inducible hypoperfusion on DSCMR that resolved on a follow up study and no patients with a negative DSCMR had any concerning symptoms or events during the time of the study. Figure 4 shows the distribution of regional inducible hypoperfusion seen in AAOLCA and AAORCA. While this study was mostly observational/feasibility, it is important to mention a few caveats. First, it was not clear which patients received surgery, although this may be published elsewhere. Many centers will operate on all patients with AAOLCA regardless of stress testing or MRI, so the utility of DSCMR in this subgroup may be less relevant. Additionally, there was no mention of any patients who had exertional symptoms but a negative DSCMR.  There was no discussion on whether any assessment of the RV could be done on MRI, a known limitation of all stress imaging tests, including MRI, and potentially more important in AAORCA. The authors discuss the lack of an evidence-based target hemodynamic response in the assessment of FPP, so it could be possible that this is not providing the same hemodynamics as exercise or in the pathophysiology of sudden cardiac death. All pediatric and sports cardiologist hope that we can find better testing to risk assess this challenging population, specifically those with AAORCA, where many are diagnosed incidentally and are asymptomatic. This study was not designed to assess negative predictive value so longer term studies will be necessary. Overall though, it is very helpful to know that this test can be done with good quality, and with more centers adding this to the arsenal of testing, hopefully we will have more meaningful data in the future.  

Left atrial strain and function in pediatric hypertrophic cardiomyopathy. Jhaveri S, Komarlu R, Worley S, Shahbah D, Gurumoorthi M, Zahka K.J Am Soc Echocardiogr. 2021 Apr 26:S0894-7317(21)00431-4. doi: 10.1016/j.echo.2021.04.014. PMID: 33915246 Take home points: Left atrial (LA) strain and dysfunction are markers of diastolic dysfunction, associated with poor exercise capacity in hypertrophic cardiomyopathy patients. Children with phenotype positive hypertrophic cardiomyopathy have reduced LA function, measurable by both volumetric and strain analysis. LA conduit function, LA reservoir function and LA reservoir strain were lower in Phenotype positive hypertrophic cardiomyopathy than in Genotype positive and phenotype negative patients. Children with phenotypic HCM have lower left atrial strain values. Altered LA mechanics are associated with poor exercise capacity. Lower LA conduit function is associated with worsened aerobic capacity in pediatric HCM.         Commentary from Dr. Manoj Gupta (New York, USA), chief section editor of Pediatric & Fetal Cardiology Journal Watch Introduction Literature on the assessment of diastolic dysfunction in pediatric HCM has focused primarily on the use of tissue Doppler indices, left atrial (LA) size, and inflow patterns. Research in adult HCM has shown that LAS values are independently associated with adverse outcomes, including heart failure, worsened exercise capacity, arrhythmias, stroke, and death. Left atrial Parameters Volumetric analysis of the left atrium was performed from apical four-chamber and two chamber views and was indexed to body surface area. LA volume (LAV) was collected at three points in the cardiac cycle as follows: (1) maximum LAV just before mitral valve opens (LAV max), (2) minimal LAV at the end of diastole when the mitral valve closes (LAV min), and (3) LAV just before atrial systole, before the p wave on electrocardiography (LAV pre-A). Reservoir function = LAV max - LAV min/ LAV min Conduit function = LAV max - LAV pre-A/LAV max Booster pump function = LAV pre-A - LAV min/LAV pre-A RESULTS The HCM cohort consisted of 78 subjects with a median age of 16 years (range, 3–25 years), of whom 60 (64%) were male). Phenotypic criteria for HCM were present in 59% patients (P+ group, n = 46) whereas the remaining carried the genotype but lacked phenotypic characteristics (G+P- group, n = 32). (Table 1) Diastolic Parameters The maximal LA volume index (LAVI) was higher in patients with P+ HCM compared with the G+P- and control groups (median, 28 vs 20 vs 19 mL/m2 , respectively; P < .001). Nearly one third of the P+ group (32% [n = 14]) had LAVI > 34 mL/m2 , which is the adult cutoff for LA dilation. Higher LAVI was associated with higher NTproBNP (r = 0.43; 95% CI, 0.05–0.71; P = .029). DISCUSSION Left atrial strain and volumetric function parameters were significantly lower in patients with phenotypic (P+) HCM compared with those with a positive genotype but without significant hypertrophy (G+P-). On the basis of these results and known literature, it can be concluded that children with HCM have impaired reservoir and conduit function, similar to their adult counterparts. However, given that they have preserved contractile pump function in childhood years, it can be speculated that changes in their atrial contractile function probably take place as they age. CONCLUSION Altered atrial mechanics, as measured by volumetric and strain analysis, are present even in the pediatric population with phenotypic HCM.