Atrial function in the Fontan circulation: comparison with invasively assessed systemic ventricular filling pressure.
Veldtman G, Possner M, Mohty D, Issa Z, Alsaleh M, AlMarzoog AT, Emmanual S, Salam Y, AlHabdan MS, Alsaied T, Rathod RH, Siblini G, Vriz O.Int J Cardiovasc Imaging. 2021 May 29. doi: 10.1007/s10554-021-02298-w. Online ahead of print.PMID: 34052973
Take Home Points:
- In patients with a biventricular circulation, atrial mechanics may be analysed to make an assessment of LV filling pressures i.e. diastolic function. Whether the same holds true in patients with a Fontan circulation is unknown.
- This observational study sought to assess the relationship between atrial mechanics and directly measured haemodynamic variables.
- Thirty nine patients with a Fontan circulation were analysed – all had TTE and cardiac catheter studies performed within 48 hours. All Fontan types were TCPC.
- Comparison was made to forty age and sex matched subjects with normal cardiac anatomy.
- Mean age 10.2 +/- 6.7 years and nearly two thirds were male (n=24).
- No association between atrial strain measurements and ventricular filling pressures was identified.
- Global atrial strain was not correlated to segmental atrial strain in the pulmonary venous atrium.
- Global atrial reservoir strain was positively correlated with pulmonary vascular resistance (r=0.51, p=0.045). Global atrial conduit strain was positively correlated with E/A ratio of AV valve inflow (r=0.56, p=0.002).
- Direct cardiac catheter measurements remain very important and at this stage cannot (and may never) be substituted by surrogate echo measurements.
Commentary by Dr. Damien Cullington (Liverpool, UK), section editor of ACHD Journal Watch:
As we are all acutely aware on a seemingly ever more frequent basis, patients with a Fontan circulation are at times exquisitely finely haemodynamically tuned. The interaction between atrial, ventricular and pulmonary vascular haemodynamics is thinly understood.
The authors screened 300 patients with a Fontan circulation. All patients with an AP type Fontan were excluded, as were patients with moderate or worse AV valve regurgitation. Other exclusion criteria were patients with AF, frequent ectopic beats or junctional rhythm, significant LVOTO and poor echo windows. In total, 39 patients were selected for analysis and the characteristics were shown in Table 1.
Atrial and ventricular strain was measured offline by Image Arena which is validated for strain analysis based on raw data extracted from different vendors and is vendor-independent. All measurements were performed on an apical 4 chamber view during 1-2 cardiac loops.
Global atrial strain measurements were measured from the entire common atrium (Figure 1) and segmental strain from the lateral wall of the left sided atrium – from the left AV groove up to the left atrial roof. As one would expect, the lateral right atrial wall cannot be assessed. The peak of the R wave as used as the initiation of the strain calculation to determine atrial reservoir, contractile and conduit strain. Atrial reservoir strain was defined as the first peak positive atrial strain – measuring atrial compliance. Atrial contractile strain was defined as the second positive peak atrial strain after the P wave, reflecting atrial contractile function. Atrial conduit strain was calculated as the difference between atrial reservoir and atrial contractile strain and reflects the passive atrial emptying phase (Figure 2).
Atrial and Ventricular strain results
No correlation was seen between global and segmental atrial strain. The global atrial reservoir strain was associated with PVR (0.51, p=0.04). There was no correlation seen between ventricular global longitudinal and free wall strain and Fontan pressure. Global atrial strain is in lower in patients who have had Fontan palliation compared to normal subjects but this is to be expected given varying degrees of atrial scarring/fibrosis resulting from instrumentation. Atrial strain measurements and cardiac catheter measured filling pressures do not correlate.
The authors highlight that echo and catheter assessment were not done simultaneously but they were within a 48 hour window. Also, catheter measures may have been taken either under local or general anaesthesia and some patients may have been relatively more dehydrated than others. Comment is made that ‘the sample size was relatively small, and statistical ‘aberrations’ masquerading as positive correlations cannot be excluded. Strain analysis of the atria in this group was challenging due to the heterogeneous anatomy.
This study did not show any correlation between directly measured filling pressures and echo derived measures which is similar to other published data. The data suggests that strain analysis in this niche group of patients should not be used as a surrogate for filling pressures.
Despite the negative findings, they are still very important since they clearly highlight the continuing importance of direct catheter based pressure measurements to inform the longer term management of patients with a Fontan circulation.