Exercise stress CMR reveals reduced aortic distensibility and impaired right-ventricular adaptation to exercise in patients with repaired tetralogy of Fallot

Myocardial, Valvular and Vascular Abnormalities in Repaired Tetralogy of Fallot

Tetralogy of Fallot is the most common heart defect associated with cyanosis characterized by the co-occurrence of pulmonary stenosis, right ventricular hypertrophy, and ventricular septal defect with over-riding of the aorta. The present review purposed to summarize myocardial, valvular and vascular abnormalities, which were described in a series of patients following repair of tetralogy of Fallot. It was also aimed to describe potential differences in these parameter using different surgical strategies.

Standardizing submaximal exercise intensities for use of supine push-pull exercise during cardiovascular magnetic resonance

BACKGROUND

Cardiovascular magnetic resonance (CMR) imaging during supine exercise at (sub)maximal oxygen consumption (VO₂ ) offers unique diagnostic insights. However, maximal VO₂ is not achievable in the supine position and standardizing submaximal exercise intensities remains challenging. Using heart rate or workload could be a viable option to translate VO₂ -based submaximal exercise intensities.

AIM

To translate submaximal exercise intensities upright cycling exercise (UCE) to supine push-pull exercise (SPPE), by comparing heart rate or workload determined during UCE, with heart rate and workload during SPPE at similar exercise intensities.

METHODS AND RESULTS

Sixteen healthy young adults (20.4 ± 2.2 years; 8 female) underwent cardiopulmonary UCE and SPPE testing [mean ± standard deviation maximal VO₂ : 3.2 ± 0.6 vs. 5 ± 0.3 L min^-1 , p < 0.001 and median (interquartile range) of the maximum workload: 310 (244, 361) vs. 98 (98, 100), p < 0.001, respectively]. Heart rate at 40% and 60% of maximal VO₂ , as determined by UCE, showed low bias (-3 and 0 bpm, respectively) and wide limits of agreement (±26 and ±28 bpm, respectively), in Bland-Altman analysis. VO₂ /Workload relation was exponential and less efficient during SPPE compared to UCE. Generalized estimated equation analysis predicted model-based mean workload during SPPE, with acceptable 95% confidence interval.

CONCLUSION

Heart rate during UCE at submaximal exercise intensities can reasonably well be used to for SPPE in healthy subjects. Using workload, an ergometer specific, model-based mean can be used to determine exercise intensities during SPPE. Individual variations in response to posture and movement change are high. During clinical interpretation of exercise CMR, individual exercise intensity has to be considered.

Validation and quantification of left ventricular function during exercise and free breathing from real-time cardiac magnetic resonance images

Exercise cardiovascular magnetic resonance (CMR) can unmask cardiac pathology not evident at rest. Real-time CMR in free breathing can be used, but respiratory motion may compromise quantification of left ventricular (LV) function. We aimed to develop and validate a post-processing algorithm that semi-automatically sorts real-time CMR images according to breathing to facilitate quantification of LV function in free breathing exercise. A semi-automatic algorithm utilizing manifold learning (Laplacian Eigenmaps) was developed for respiratory sorting. Feasibility was tested in eight healthy volunteers and eight patients who underwent ECG-gated and real-time CMR at rest. Additionally, volunteers performed exercise CMR at 60% of maximum heart rate. The algorithm was validated for exercise by comparing LV mass during exercise to rest. Respiratory sorting to end expiration and end inspiration (processing time 20 to 40 min) succeeded in all research participants. Bias ± SD for LV mass was 0 ± 5 g when comparing real-time CMR at rest, and 0 ± 7 g when comparing real-time CMR during exercise to ECG-gated at rest. This study presents a semi-automatic algorithm to retrospectively perform respiratory sorting in free breathing real-time CMR. This can facilitate implementation of exercise CMR with non-ECG-gated free breathing real-time imaging, without any additional physiological input.

Pressure-volume relationship by pharmacological stress cardiovascular magnetic resonance

The variation between rest and peak stress end-systolic pressure-volume relation (ΔESPVR) is an index of myocardial contractility, easily obtained during routine stress echocardiography and never tested during dipyridamole stress-cardiac magnetic resonance (CMR). We assessed the ΔESPVR index in patients with known/suspected coronary artery disease (CAD) who underwent dipyridamole stress-CMR. One-hundred consecutive patients (24 females, 63.76 ± 10.17 years) were considered. ESPVR index was evaluated at rest and stress from raw measurement of systolic arterial pressure and end-systolic volume by biplane Simpson's method. The ΔESPVR index showed a good inter-operator reproducibility. Mean ΔESPVR index was 0.48 ± 1.45 mmHg/mL/m2. ΔESPVR index was significantly lower in males than in females. ΔESPVR index was not correlated to rest left ventricular end-diastolic volume index or ejection fraction. Forty-six of 85 patients had myocardial fibrosis detected by the late gadolinium enhancement technique and they showed significantly lower ΔESPVR values. An abnormal stress CMR was found in 25 patients and they showed significantly lower ΔESPVR values. During a mean follow-up of 56.34 ± 30.04 months, 24 cardiovascular events occurred. At receiver-operating characteristic curve analysis, a ΔESPVR < 0.02 mmHg/mL/m2 predicted the presence of future cardiac events with a sensitivity of 0.79 and a specificity of 0.68. The noninvasive assessment of the ΔESPVR index during a dipyridamole stress-CMR exam is feasible and reproducible. The ΔESPVR index was independent from rest LV dimensions and function and can be used for a comparative assessment of patients with different diseases. ΔESPVR index by CMR can be a useful and simple marker for additional prognostic stratification.

Systolic and diastolic functional reserve of the subpulmonary and systemic right ventricles as assessed by pharmacologic and exercise stress: A systematic review

We performed a systematic review of the literature on the assessment of subpulmonary and systemic right ventricular (RV) functional reserve during pharmacological and exercise stress in congenital heart patients and patients with pulmonary arterial hypertension (PAH). Literature search was conducted using PubMed, EMBASE, and MEDLINE from their inception up to August 2020. Of 913 records identified, 56 studies with a total of 1730 patients were included. Of the 56 studies, 23 assessed subpulmonary RV functional reserve in repaired tetralogy of Fallot patients, 19 assessed systemic RV reserve in patients with transposition of the great arteries (TGA) after atrial switch and those with congenitally corrected TGA, and 14 assessed subpulmonary RV research in patients with PAH. Pharmacological and exercise stress was used, respectively, in 22 and 34 studies. The main findings were (1) impairment of RV systolic and diastolic functional reserve, (2) associations between impaired functional reserve and worse baseline functional parameters, and (3) prognostic implications of RV systolic functional reserve on clinical outcomes in patients with volume and/or pressure-loaded subpulmonary and systemic right ventricles. Further studies are required to establish the incremental value of incorporating stress studies of RV systolic and diastolic function in the clinical management algorithm of congenital heart patients and patients with PAH.

Impaired Exercise Tolerance in Repaired Tetralogy of Fallot Is Associated With Impaired Biventricular Contractile Reserve: An Exercise-Stress Real-Time Cardiovascular Magnetic Resonance Study

BACKGROUND

Correction of tetralogy of Fallot (cTOF) often results in pulmonary valve pathology and right ventricular (RV) dysfunction. Reduced exercise capacity in cTOF patients cannot be explained by these findings alone. We aimed to explore why cTOF patients exhibit impaired exercise capacity with the aid of a comprehensive cardiopulmonary exercise testing (CPET) and real-time cardiovascular magnetic resonance exercise testing (CMR-ET) protocol.

METHODS

Thirty three cTOF patients and 35 matched healthy controls underwent CPET and CMR-ET in a prospective case-control study. Real-time steady-state free precession cine and phase-contrast sequences were obtained during incremental supine in-scanner cycling at 50, 70, and 90 W. RV and left ventricle (LV) volumes and pulmonary blood flow (Qp) were calculated. Differences of CPET and CMR-ET between cTOF versus controls and correlations between CPET and CMR-ET parameters in cTOF were evaluated statistically for all CMR exercise levels using Mann-Whitney U and Spearman rank-order correlation tests.

RESULTS

CPET capacity was significantly lower in cTOF than in controls. cTOF patients exhibited not only significantly reduced Qp and RV function but also lower LV function on CMR-ET. Higher CPET values in cTOF correlated with higher Qp (Qp 90 W versus carbon dioxide ventilatory equivalent %: R=-0.519, P<0.05), higher LV-end-diastolic volume indexed to body surface area (LV-end-diastolic volume indexed to body surface area at 50 W versus oxygen uptake in % at maximum exercise on CPET R=0.452, P<0.05), and change in LV ejection fraction (EF; LV-EF at 90 W versus Watt %: r=-0.463, P<0.05). No correlation was found with regard to RV-EF. Significant RV-LV interaction was observed during CMR-ET (RV-EF versus LV-EF at 50 W and 70 W: r=0.66, P<0.02 and r=0.52, P<0.05, respectively).

CONCLUSIONS

Impaired exercise capacity in cTOF resulted from a reduction in not only RV, but also LV function. cTOF with good exercise capacity on CPET demonstrated higher LV reserve and pulmonary blood flow during incremental CMR-ET. Apart from RV parameters, CMR-ET-derived LV function could be a valuable tool to stratify cTOF patients for pulmonary valve replacement.

The challenges of an aging tetralogy of Fallot population

Introduction: Advancements in surgery and management have resulted in a growing population of aging adults with tetralogy of Fallot (TOF). As a result, there has been a parallel growth in late complications associated with the sequelae from the underlying cardiac anomalies as well as the surgical and other interventional treatments.Areas covered: Here, we review challenges related to an aging population of patients with TOF, particularly late complications, and highlight advances in management and key areas for future research. Pulmonary regurgitation, heart failure, arrhythmias, and aortic complications are some of these late complications. There is also a growing incidence of acquired cardiovascular disease, obesity, and diabetes associated with aging. Management of these late complications and acquired comorbidities continues to evolve as research provides insights into long-term outcomes from medical therapies and surgical interventions.Expert opinion: The management of an aging TOF population will continue to transform with advances in imaging technologies to identify subclinical disease and valve replacement technologies that will prevent and mitigate disease progression. In the coming years, we speculate that there will be more data to support the use of novel heart failure therapies in TOF and consensus guidelines on the management of refractory arrhythmias and aortic complications.

Exercise Cardiovascular Magnetic Resonance: A Review

While pharmacologic stress cardiovascular magnetic resonance imaging (MRI) is a robust noninvasive tool in the diagnosis and prognostication of epicardial coronary artery disease, clinical guidelines recommend exercise-based testing in those patients who can exercise. This review describes the development of exercise cardiovascular MRI protocols, summarizes the insights across various patient populations, and highlights future research initiatives. LEVEL OF EVIDENCE: 5 TECHNICAL EFFICACY: Stage 2.

The aortic root in repaired tetralogy of Fallot: Serial measurements and impact of losartan treatment

BACKGROUND

Aortic root dilatation is common in adults with repaired tetralogy of Fallot (rTOF) and might lead to aortic dissection. However, little is known on progression of aortic dilatation and the effect of pharmaceutical treatment. This study aims to determine factors associated with aortic growth and investigate effects of losartan.

METHODS AND RESULTS

We performed a prespecified analysis from the 1:1 randomized, double-blind REDEFINE trial. Aortic root diameters were measured at baseline and after 2.0 ± 0.3 years of follow-up using cardiovascular magnetic resonance (CMR) imaging. A total of 66 patients were included (68% men, age 40 ± 12 years, baseline aortic root 37 ± 6 mm, 32% aortic dilatation (>40 mm)). There was a trend towards slow aortic root growth (+0.6 ± 2.3 mm after two years, p = 0.06) (n = 60). LV stroke volume was the only factor associated with both a larger baseline aortic root (β: 0.09 mm/ml (95% C.I.:0.02, 0.15), p = 0.010) and with aortic growth during follow-up (β: 0.04 mm/ml (95% C.I.:0.005, 0.066), p = 0.024), after correction for age, sex, and body surface area using linear regression analysis. No treatment effect of losartan was found (p = 0.17).

CONCLUSIONS

Aortic root dilatation was present in about one-third of rTOF patients. A larger LV stroke volume was associated with both a larger baseline aortic root and ongoing growth. Our findings provide no arguments for lower aortic diameter thresholds for prophylactic surgery compared to the general population.

Exercise cardiovascular magnetic resonance: development, current utility and future applications

Stress cardiac imaging is the current first line investigation for coronary artery disease diagnosis and decision making and an adjunctive tool in a range of non-ischaemic cardiovascular diseases. Exercise cardiovascular magnetic resonance (Ex-CMR) has developed over the past 25 years to combine the superior image qualities of CMR with the preferred method of exercise stress. Presently, numerous exercise methods exist, from performing stress on an adjacent CMR compatible treadmill to in-scanner exercise, most commonly on a supine cycle ergometer. Cardiac conditions studied by Ex-CMR are broad, commonly investigating ischaemic heart disease and congenital heart disease but extending to pulmonary hypertension and diabetic heart disease. This review presents an in-depth assessment of the various Ex-CMR stress methods and the varied pulse sequence approaches, including those specially designed for Ex-CMR. Current and future developments in image acquisition are highlighted, and will likely lead to a much greater clinical use of Ex-CMR across a range of cardiovascular conditions.

Feasibility of Cardiovascular Four-dimensional Flow MRI during Exercise in Healthy Participants

Purpose

To explore the feasibility of using four-dimensional (4D) flow MRI to quantify blood flow and kinetic energy (KE) in the heart during strenuous exercise.

Materials and Methods

For this prospective study, cardiac 4D flow MRI was performed in 11 healthy young adult participants (eight men, three women; mean age, 26 years ± 1 [standard deviation]) at rest and during exercise with an MRI-compatible exercise stepper between March 2016 and July 2017. Flow was measured in the ascending aorta (AAo) and main pulmonary artery (MPA). KE was quantified in the left and right ventricle. Significant changes in flow and KE during exercise were identified by using t tests. Repeatability was assessed with inter- and intraobserver comparisons and an analysis of internal flow consistency.

Results

Nine participants successfully completed both rest and exercise imaging. Internal flow consistency analysis in systemic and pulmonary circulation showed average relative differences of 10% at rest and 16% during exercise. For flow measurements in the AAo and MPA, relative differences between observers never exceeded 6% in any vessel and showed excellent correlation, even during exercise. Relative differences were increased for KE, typically on the order of 30%, with poor interobserver correlation between measurements.

Conclusion

Four-dimensional flow MRI can quantify increases in flow in the AAo and MPA during strenuous exercise and is highly repeatable. KE had reduced repeatability because of suboptimal segmentation methods and requires further development before clinical implementation. Supplemental material is available for this article. © RSNA, 2020See also the commentary by Markl and Lee in this issue.