Exercise-dependent changes in ventricular-arterial coupling and aortopulmonary collateral flow in Fontan patients: a real-time CMR study

AIMS

Inefficient ventricular-arterial (V-A) coupling has been described in Fontan patients and may result in adverse haemodynamics. A varying amount of aortopulmonary collateral (APC) flow is also frequently present that increases volume load of the single ventricle. The aim of the study was to assess changes in V-A coupling and APC flow during exercise CMR.

METHODS AND RESULTS

Eighteen Fontan patients (age 24 ± 3 years) and 14 controls (age 23 ± 4 years) underwent exercise CMR using a cycle ergometer. Ventricular volumetry and flow measurements in the ascending aorta (AAO), inferior (IVC), and superior (SVC) vena cava were assessed using real-time sequences during stepwise increases in work load. Measures of systemic arterial elastance Ea, ventricular elastance Ees, and V-A coupling (Ea/Ees) were assessed. APC flow was quantified as AAO - (SVC + IVC). Ea remained unchanged during all levels of exercise in both groups (P = 0.39 and P = 0.11). Ees increased in both groups (P = 0.001 and P < 0.001) with exercise but was lower in the Fontan group (P = 0.04). V-A coupling was impaired in Fontan patients at baseline (P = 0.04). Despite improvement during exercise (P = 0.002) V-A coupling remained impaired compared with controls (P = 0.001). Absolute APC flow in Fontan patients did not change during exercise even at maximum work load (P = 0.98).

CONCLUSIONS

Inefficient V-A coupling was already present at rest in Fontan patients and aggravated during exercise due to a limited increase in ventricular contractility which demonstrates the importance of a limited functional reserve of the single ventricle. APC flow remained unchanged suggesting no further increase in volume load during exercise.

Bioelastic properties of the aorta in children, adolescents and young adults after cardiac transplantation: a cardiovascular magnetic resonance study

Background

Long-term complications after cardiac transplantation are common and typically include arterial hypertension and coronary allograft vasculopathy. Few studies also suggested that heart transplant recipients have an increased arterial stiffness.

Purpose

This prospective study aimed to assess the bioelastic properties of the aorta as well as LV function, morphology and structure in children and young adults after cardiac transplantation.

Methods

CMR studies from 34 patients (median age: 17.1 years, range: 8–24 years) who underwent cardiac transplantation in childhood were analysed. Aortic anatomy and distensibility were assessed at five locations of the thoracic aorta using steady-state free precession cine sequences. Pulse wave velocity (PWV) of the aortic arch and the descending thoracic aorta was measured from 2-dimensional phase contrast images. Size and function of the left atrium and the ventricles were assessed from a stack of short axis slices. Myocardial T1 times were determined using a standard MOLLI sequence.

Results

Cross-sectional areas of the ascending aorta and the aortic arch tended to be lower in patients compared to controls (ascending aorta 464.5±172.5 mm2 vs. 515.3±186.3 mm2, aortic arch 342.4±113.3 mm2 vs. 376.9±148.5 mm2) whereas cross-sectional areas of the descending aorta tended to be higher (aortic isthmus 283.7±102.1 mm2 vs. 257.9±89.5 mm2, aorta descendens diaphragmal 218.4±75.8 mm2 vs. 214.2±75.0 mm2) and showed a correlation with systolic blood pressure (r=0.33). PWV was higher in the aortic arch (4.8±2.4 m/s vs. 3.6±0.7 m/s).

Aortic distensibility was slightly higher at all measuring points in the study population compared to the control group and showed an increase with rising distance from the heart (ascending aorta 10.5±5.8 10–3 mm Hg-1, aortic isthmus 13.1±7.5 10–3 mm Hg-1, descending aorta 16.6±6.8 10–3 mm Hg-1). Biventricular volumes were slightly reduced in the patient group compared to the control group but this was not statistically significant. Only left ventricular mass messured during the systolic phase was higher in the study population compared to the control group (males 55.1 g/m2 vs. 53.0 g/m2, females 46.2 g/m2 vs. 45.2 g/m2). T1 mapping demonstrated increased T1 times in the heart-transplanted group compared to published data in healthy adults. In particular, T1 times of the lateral and inferior myocardial segments were higher.

Conclusion

Patients who underwent cardiac transplantation in childhood seem to have a reduced bioelasticity of the thoracic aorta. Increased myocardial T1 times suggesting alterations in myocardial structure.

Funding Acknowledgement

Type of funding sources: None.

Effect of Inhaled Nitric Oxide on Blood Flow Dynamics in Patients After the Fontan Procedure Using Cardiovascular Magnetic Resonance Flow Measurements

Invasive hemodynamic studies have shown that nitric oxide (NO), a selective pulmonary vasodilator, can lower pulmonary vascular resistance in Fontan patients. Because oximetry-derived flow quantification may be unreliable, we sought to detect changes in blood flow within the Fontan circulation after inhalation of NO using cardiovascular magnetic resonance (CMR). Thirty-three patients (mean age 12.8 ± 7.0 years) after the Fontan procedure underwent CMR as part of their routine clinical assessment. Standard two-dimensional blood flow measurements were performed in the Fontan tunnel, superior vena cava (SVC) and ascending aorta (AAO) before and after inhalation of 40 ppm NO for 8-10 min. Systemic-to-pulmonary collateral (SPC) flow was calculated as AAO - (SVC + tunnel). Heart rate (82 ± 18 to 81 ± 18 bpm; p = 0.31) and transcutaneous oxygen saturations (93 ± 4 to 94 ± 3 %; p = 0.13) did not change under NO inhalation. AAO flow (3.23 ± 0.72 to 3.12 ± 0.79 l/min/m(2); p = 0.08) decreased, tunnel flow (1.58 ± 0.40 to 1.65 ± 0.46 l/min/m(2); p = 0.032) increased, and SVC flow (1.01 ± 0.39 to 1.02 ± 0.40 l/min/m(2); p = 0.50) remained unchanged resulting in higher total caval flow (Qs) (2.59 ± 0.58 to 2.67 ± 0.68 l/min/m(2); p = 0.038). SPC flow decreased significantly from 0.64 ± 0.52 to 0.45 ± 0.51 l/min/m(2) (p = 0.002) and resulted in a significant decrement of the Qp/Qs ratio (1.23 ± 0.23 to 1.15 ± 0.23; p = 0.001). Inhalation of NO in Fontan patients results in significant changes in pulmonary and systemic blood flow. The reduction in SPC flow is accompanied by a net increase in effective systemic blood flow suggesting beneficial effects of pulmonary vasodilators on cardiac output, tissue perfusion and exercise capacity.

Focal myocardial fibrosis assessed by late gadolinium enhancement cardiovascular magnetic resonance in children and adolescents with dilated cardiomyopathy

BACKGROUND

Different patterns of late gadolinium enhancement (LGE) including mid-wall fibrosis using cardiovascular magnetic resonance (CMR) have been reported in adult patients presenting with non-ischemic dilated cardiomyopathy (DCM). In these studies, LGE was associated with pronounced LV remodelling and predicted adverse cardiac outcomes. Accordingly, the purpose of our study was to determine the presence and patterns of LGE in children and adolescents with DCM.

METHODS

Patients <18 years of age presenting with severe congestive heart failure who were admitted for evaluation of heart transplantation at our centre underwent CMR examination which consisted of ventricular functional analysis and assessment of LGE for detection of myocardial fibrosis. Ischemic DCM was excluded by coronary angiography, and right ventricular endomyocardial biopsies ruled out acute myocarditis.

RESULTS

Thirty-one patients (mean age 2.1 ± 4.2 years) with severe LV dilatation (mean indexed LVEDV 136 ± 48 ml/m(2)) and LV dysfunction (mean LV-EF 23 ± 8%) were examined. LGE was detected in 5 of the 31 patients (16%) appearing in various patterns characterized as mid-wall (n = 1), focal patchy (n = 1), RV insertion site (n = 1) and transmural (n = 2). Based on histopathological analysis, 4 of the 5 LGE positive patients had lymphocytic myocarditis, whereas one patient was diagnosed with idiopathic DCM.

CONCLUSIONS

In children and adolescents with DCM, focal histologically proven myocardial fibrosis is rarely detected by LGE CMR despite marked LV dilatation and severely depressed LV function. LGE occurred in various patterns and mostly in patients with inflammatory cardiomyopathy. It remains unclear whether myocardial fibrosis in childhood DCM reflects different endogenous repair mechanisms that enable favourable reverse remodelling. Larger trials are needed to assess the prognostic implications of LGE in childhood DCM.

Cardiovascular magnetic resonance assessment of ventricular function and myocardial scarring before and early after repair of anomalous left coronary artery from the pulmonary artery

BACKGROUND

In patients with anomalous left coronary artery from the pulmonary artery (ALCAPA) left ventricular (LV) dilatation and dysfunction evolves due to diminished myocardial perfusion caused by coronary steal phenomenon. Using late gadolinium enhanced cardiovascular magnetic resonance (LGE-CMR) imaging, myocardial scarring has been shown in ALCAPA patients late after repair, however the incidence of scarring before surgery and its impact on postoperative course after surgical repair remained unknown.

METHODS

8 ALCAPA-patients (mean age 10.0 ± 5.8 months) underwent CMR before and early after (mean 4.9 ± 2.5 months) coronary reimplantation procedures. CMR included functional analysis and LGE for detection of myocardial scars.

RESULTS

LV dilatation (mean LVEDVI 171 ± 94 ml/m2) and dysfunction (mean LV-EF 22 ± 10 %) was present in all patients and improved significantly after surgery (mean LVEDV 68 ± 42 ml/m2, p=0.02; mean LV-EF 58 ± 19 %, p<0.001). Preoperative CMR revealed myocardial scarring in 2 of the 8 patients and did not predict postoperative course. At follow-up CMR, one LGE-positive patient showed delayed recovery of LV function while myocardial scarring was still present in both patients. In two patients new-onset transmural scarring was found, although functional recovery after operation was sufficient. One of them showed a stenosis of the left coronary artery and required resurgery.

CONCLUSIONS

Despite diminished myocardial perfusion and severely compromised LV function, myocardial scarring was preoperatively only infrequently present. Improvement of myocardial function was independent of new-onset scarring while the impact of preoperative scarring still needs to be defined.

Aortopulmonary collateral flow is related to pulmonary artery size and affects ventricular dimensions in patients after the fontan procedure

BACKGROUND

Aortopulmonary collaterals (APCs) are frequently found in patients with a single-ventricle (SV) circulation. However, knowledge about the clinical significance of the systemic-to-pulmonary shunt flow in patients after the modified Fontan procedure and its potential causes is limited. Accordingly, the aim of our study was to detect and quantify APC flow using cardiovascular magnetic resonance (CMR) and assess its impact on SV volume and function as well as to evaluate the role of the size of the pulmonary arteries in regard to the development of APCs.

METHODS

60 patients (mean age 13.3 ± 6.8 years) after the Fontan procedure without patent tunnel fenestration underwent CMR as part of their routine clinical assessment that included ventricular functional analysis and flow measurements in the inferior vena cava (IVC), superior vena cava (SVC) and ascending aorta (Ao). APC flow was quantified using the systemic flow estimator: (Ao) - (IVC + SVC). Pulmonary artery index (Nakata index) was calculated as RPA + LPA area/body surface area using contrast enhanced MR angiography. The patient cohort was divided into two groups according to the median APC flow: group 1 < 0.495 l/min/m(2) and group 2 > 0.495 l/min/m(2).

RESULTS

Group 1 patients had significant smaller SV enddiastolic (71 ± 16 vs 87 ± 25 ml/m(2); p=0.004) and endsystolic volumes (29 ± 11 vs 40 ± 21 ml/m(2); p=0.02) whereas ejection fraction (59 ± 9 vs 56 ± 13%; p=0.38) differed not significantly. Interestingly, pulmonary artery size showed a significant inverse correlation with APC flow (r=-0.50, p=0.002).

CONCLUSIONS

Volume load due to APC flow in Fontan patients affected SV dimensions, but did not result in an impairment of SV function. APC flow was related to small pulmonary artery size, suggesting that small pulmonary arteries represent a potential stimulus for the development of APCs.

Beneficial effects of residual right ventricular outflow tract obstruction on right ventricular volume and function in patients after repair of tetralogy of Fallot

Preservation of the pulmonary valve, even at the expense of a mild residual stenosis, is the current surgical policy for the management of patients with tetralogy of Fallot (TOF). This study aimed to assess the long-term effect of a residual right ventricular outflow tract obstruction (RVOTO) on RV dimension and function. This study prospectively assessed 53 children (mean age, 13.4 ± 6.4 years) after repair of TOF using cardiovascular magnetic resonance imaging. Residual RVOTO on echocardiography was defined as a peak systolic RVOT gradient of 25 mmHg or higher. Patients with RVOTO (n = 29) had significantly less pulmonary regurgitation (25.2 ± 10.6 %) than patients without RVOTO (30.8 ± 9.3 %; p = 0.05) (n = 24). Compared with patients who had no RVOTO, children with RVOTO had significantly smaller RV end-diastolic volume (94.0 ± 2.6 vs 104.0 ± 20.7 ml/m(2); p < 0.05) and end-systolic volume (42.9 ± 20.0 vs 48.9 ± 13.2 ml/m(2); p < 0.05), whereas RV ejection fraction did not differ significantly between the two groups (55.5 ± 8.4 vs 54.0 ± 6.6 %). Restrictive physiology, assessed by late diastolic forward flow in the main pulmonary artery, was equally distributed within the two groups (31 vs 25 %; nonsignificant difference). According to the study data, residual RVOTO after repair of TOF does not affect RV function, whereas RV dimensions and the degree of pulmonary regurgitation are more favorable in the long-term follow-up evaluation of those patients. These results confirm the beneficial effects of the current strategy for repair of TOF.