Background
Differences in single right ventricle (SRV) and single left ventricles (SLV) function are poorly described, although myocardial dysfunction is an important risk factor for morbidity and mortality. The aims of this study were to compare function between patients with SRVs and those with SLVs using newer echocardiographic techniques and to determine differences across staged palliation.
Methods
In this cross-sectional study comparing 30 patients with SRVs and 30 with SLVs of similar ages (2.5 ± 1.7 vs 2.6 ± 1.6 years), patients were matched for surgical stage (20 pre–bidirectional cavopulmonary anastomosis, 20 pre-Fontan, and 20 post-Fontan patients). Circumferential and longitudinal strain, strain rate (SR), early diastolic SR, postsystolic strain index, and myocardial dyssynchrony index were measured. Comparisons between SRV and SLV parameters were made as a whole group and by subanalysis at each surgical stage.
Results
Patients with SRVs had reduced systolic SRs (circumferential: −1.0%/sec vs −1.2%/sec, P = .01; longitudinal: −1.1%/sec vs −1.3%/sec, P = .002), reduced early diastolic SRs (circumferential: 1.4%/sec vs 1.9%/sec, P = .03; longitudinal: 1.6%/sec vs 2.2%/sec, P = .001), and increased circumferential postsystolic strain indexes (8% vs 0%, P < .0001). Subanalysis at each surgical stage showed that the greatest disparity in systolic parameters occurred before bidirectional cavopulmonary anastomosis (longitudinal SR, P = .009; postsystolic strain index, P = .005) and that parity was regained after the Fontan procedure, while traditional diastolic parameters (E velocity, P = .004; E/E′ ratio, P = .0003) were reduced in patients with SRVs after the Fontan procedure.
Conclusions
The SRV has reduced contractility and diastolic function compared with the SLV. Ventricular systolic performance in patients with SRVs was poorest before bidirectional cavopulmonary anastomosis, while differences in diastolic function were more prominent after Fontan completion.
The outcomes of patients with single ventricles have greatly improved because of advances in surgical techniques and postoperative care, but long-term survival remains guarded. Important risk factors for morbidity and mortality include ventricular dysfunction and atrioventricular valve regurgitation. The morphologic right ventricle is less suited to the systemic circulation, as systemic right ventricular failure is seen in congenital and surgically corrected transposition of the great arteries. Several outcome series have suggested that systemic single right ventricle (SRV) hearts are associated with increased mortality. However, this assertion remains controversial, as other series have found no difference between morphologic single left ventricles (SLVs) and SRVs. Differences in SRV and SLV function remain poorly defined. Conventional echocardiographic measures are limited by geometric assumptions and load dependency, and they do not assess the complex patterns of contraction. Speckle-tracking echocardiography is a newer technique that overcomes the limitations of conventional echocardiography in the assessment of single-ventricle hearts and can be applied to both SRVs and SLVs. The objectives of this study were to examine ventricular function in single-ventricle hearts and to compare the morphologic right ventricle and left ventricle for differences in systolic and diastolic performance at different stages of palliative surgery.
Methods
Study Population
Since 2007, we have conducted a longitudinal study to examine ventricular function in patients with hypoplastic left heart syndrome (HLHS). With further study of these patients, we expanded our patient population to include all patients with single ventricles at any surgical stage in 2009. For this cross-sectional study to compare SRV and SLV function, we selected patients with SLVs from this group, who were matched for surgical stage with patients with SRVs of similar ages by an observer who was blinded to patients’ clinical courses. The enrolled patients all underwent detailed echocardiographic scans at the pre–bidirectional cavopulmonary anastomosis (BCPA), pre-Fontan, and post-Fontan stages, after a functional protocol optimized for the analysis of ventricular and atrial function. Because of the small number of patients with SLVs enrolled in the neonatal period, we were not able to perform a comparison at this stage. Therefore, all patients were compared at only one of three time points: (1) before BCPA, (2) before the Fontan procedure, or (3) after the Fontan procedure. Because the study was cross-sectional, no patient was included more than once. Parents gave informed consent to participate, and the study was approved by the Health Research Ethics Board at the University of Alberta.
Echocardiography
Two-dimensional echocardiography was performed using a Vivid 7 ultrasound platform (GE Medical Systems, Milwaukee, WI) using a 7-MHz or 5-MHz probe with electrocardiographic and respiratory recordings, with the images optimized for higher frame rates (mean, 105 ± 27 Hz). Images were obtained according to our single-ventricle protocol and included the parasternal short-axis view at the base for circumferential contraction and the apical four-chamber view for longitudinal contraction. All pre-BCPA patients were sedated per our institutional protocol using chloral hydrate (70–80 mg/kg), while patients at subsequent stages were not.
Conventional Parameters of Ventricular Function
The dominant ventricle’s global systolic function was assessed using ventricular fractional area change and the myocardial performance index. Ventricular longitudinal function was assessed using ventricular annular plane systolic excursion indexed to body surface area, color Doppler tissue imaging (DTI) S′ velocity of the dominant ventricular free wall, and isovolumic acceleration. Ventricular diastolic function was assessed using dominant ventricular inflow E and A pulsed Doppler velocities, color DTI E′ and A′ velocities of the dominant ventricular free wall, the E/E′ ratio of the ventricular free wall, and the right upper pulmonary venous S/D ratio. The degree of dominant atrioventricular valve regurgitation was qualitatively estimated as mild, moderate, or severe.
Speckle-Tracking Echocardiography
Offline two-dimensional speckle-tracking echocardiographic images were analyzed using commercially available software (EchoPAC version 7.1; GE Medical Systems). The analysis has been previously described in detail. In brief, we measured basal circumferential and longitudinal strain variables as follows. A single best cardiac loop at end-expiration was selected. The endocardium was manually traced and the region of interest for analysis adjusted to include the entire thickness of the myocardium ( Figure 1 ). The software algorithm automatically performed the analysis and returned a pass or fail grade for each of the six segments indicating whether sufficient tracking was achieved. Only images with greater than five of six successful tracking attempts were accepted for analysis. We measured the following circumferential and longitudinal strain variables: peak strain, peak strain rate (SR) and postsystolic strain index (PSSi) ([peak strain − peak systolic strain]/peak strain; Figure 2 ), myocardial dyssynchrony index (the standard deviation of time to peak strain of six segments), and early diastolic SR (EDSR) as a surrogate for ventricular relaxation. We obtained the ratio of longitudinal to circumferential strain as an index of the relative contribution of circumferential contraction to longitudinal contraction.
Statistical Analysis
All functional data are presented as medians with ranges. Comparisons between the functional parameters of patients with SRVs and those with SLVs as a whole group, as well as subanalyses for differences at each surgical stage, were performed using Wilcoxon’s rank-sum test for continuous variables. P values < .05 were considered to indicate statistically significant differences. Analyses were performed using GraphPad Prism version 5.03 (GraphPad Software, Inc., La Jolla, CA).
Results
Of 86 eligible patients with functionally single-ventricle hearts at three different stages, 60 were matched for surgical stage to allow comparison between those with SRVs ( n = 30) and those with SLVs ( n = 30) as a group. Hence, there were 20 patients with either SRVs or SLVs at each of the pre-BCPA, pre-Fontan, and post-Fontan stages. Because of a larger proportion of patients with SRVs in our study group, some with SRVs were “unmatched” and thus not included in the study. There were no significant differences between the characteristics of patients excluded and those included in the study ( Appendix ).
Patients’ characteristics and cardiac anatomic characteristics are summarized in Tables 1 and 2 . There were no differences in age, weight, oxygen saturation, and degree of atrioventricular valve regurgitation between the SRV and SLV groups. Among the patients with SRVs, 80% had HLHS, and 93% underwent their first surgery <2 months after birth, with 87% undergoing Norwood procedures with Sano shunts under cardiopulmonary bypass. The SLV population was a mixture of patients with tricuspid atresia and those with double-inlet left ventricle, with 83% of patients with SLVs undergoing their first surgery <6 months after birth, but only 20% undergoing Norwood procedures with Sano shunts. Hence, many of the patients with SLVs had other interventions not requiring cardiopulmonary bypass ( Table 3 ). Of the patients with SRVs, one patient in the pre-BCPA group died after BCPA from respiratory failure secondary to an intercurrent infection, and two patients in the post-Fontan group subsequently required heart transplantation for ventricular dysfunction. Of the patients with SLVs, one patient in the pre-Fontan group died after the Fontan procedure because of an aneurysmal rupture of the hypoplastic right ventricular free wall.
| Characteristic | SRV ( n = 30) | SLV ( n = 30) |
|---|---|---|
| Age | ||
| Pre-BCPA (mo) | 4.9 ± 2.6 | 4.8 ± 2.2 |
| Pre-Fontan (y) | 3.8 ± 0.9 | 3.7 ± 0.9 |
| Post-Fontan (y) | 3.4 ± 0.9 | 3.4 ± 0.5 |
| Weight (kg) | ||
| Pre-BCPA | 6.0 ± 1.0 | 7.2 ± 1.5 |
| Pre-Fontan | 13.8 ± 1.2 | 14.6 ± 2.3 |
| Post-Fontan | 13.4 ± 2.0 | 14.0 ± 1.8 |
| Oxygen saturation (%) | ||
| Pre-BCPA | 79 ± 3 | 83 ± 6 |
| Pre-Fontan | 81 ± 3.9 | 83 ± 5 |
| Post-Fontan | 83 ± 5 | 86 ± 6 |
| Moderate AVVR | ||
| Pre-BCPA | 0 | 1 |
| Pre-Fontan | 3 | 1 |
| Post-Fontan | 1 | 1 |
| HLHS | DORV | uAVSD | TA | DILV | Other ∗ | ||
|---|---|---|---|---|---|---|---|
| SRV | SLV | ||||||
| Pre-BCPA | 9 | 1 | 2 | 4 | 1 | 3 | |
| Pre-Fontan | 8 | 2 | 4 | 6 | |||
| Post-Fontan | 7 | 1 | 2 | 1 | 7 | 2 | |
| Total | 24 | 1 | 5 | 3 | 14 | 10 | 3 |
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