How Does the Blood Go Round in Single Ventricles and Fontans? New Horizons in...
With Dr. Andrew Reddington · StayCurrentMD
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What the experts said
40-50% of cardiac output at baseline in Fontan patients is driven directly by the work of breathing
Negative mean airway pressure during normal ventilation draws blood into the Fontan circuit
Valsalva maneuver with mean airway pressure elevated to 20 cm H2O cuts off spontaneous respiratory flow, leaving only tiny flow with ventricular systole
Low pulmonary vascular resistance is a prerequisite for good Fontan outcome
In normal individuals, nitric oxide does not reduce pulmonary vascular resistance because the pulmonary vascular bed is maximally vasodilated
Nitric oxide produced a statistically and physiologically significant fall in pulmonary vascular resistance of about 1 index wood unit in teenage Fontan patients
Only half of teenage Fontan patients showed benefit from nitric oxide
If only half of Fontan patients benefit from nitric oxide, they are unlikely to further benefit from PDE5 inhibitors
The systemic ventricle in Fontan circulation is hypercontractile to match its increased afterload
Arterial elastance is high in Fontan patients but relatively well coupled to ventricular elastance
The primary problem in Fontan ventricles is in diastole, not systole
In early post-Fontan course, it is early diastole (E wave) that is affected, not late diastole (A wave), with virtual abolishment of early rapid filling
Time constant of relaxation and isovolumic relaxation time are prolonged in early post-Fontan patients, indicative of impaired relaxation
Impaired early relaxation is due to incoordinate wall motion during isovolumic relaxation, with post-systolic shortening of one part of the ventricle causing another part to move outward
Longer isovolumic relaxation time correlates with longer hospital stay immediately after Fontan operation
Late post-Fontan patients can develop pseudonormalized filling pattern (E > A) due to rising left atrial pressure despite persistent incoordinate relaxation
In normal individuals, left ventricular end-diastolic pressure rises by about 2 mmHg per decade after age 30
Fontan patients with high diastolic stiffness may have low end-diastolic pressure because reduced preload causes the ventricle to become smaller and pressure to fall down the pressure-volume curve
Bench pressing 500 pounds essentially cuts off pulmonary blood flow in Fontan patients
Sustained Valsalva maneuvers may be particularly disadvantageous in old atrio-pulmonary Fontans due to direct effects on atrial stretch and potential for chronic atrial arrhythmias
Mayo Clinic series with longer follow-up suggests right ventricular morphology does appear to be a risk factor late after Fontan
Rise in end-diastolic pressure in normal individuals is more rapid with hypertension, diabetes, other risk factors, and ventricular volume load such as AV valve or aortic regurgitation
Fontan patients frequently have some degree of volume load and have had volume load for the first few years of life
All Fontan patients have very raised arterial impedance and systemic vascular resistance
There is no evidence-based role for ACE inhibition or arterial vasodilators in short-term Fontan management, as systemic vasodilation drops cardiac output
Management of left ventricular end-diastolic pressure, fibrosis, and vascular biology have real potential as therapeutic targets in long-term Fontan management
Understanding the impact of long-term therapies for diastolic dysfunction will require 10-20 years of follow-up
The difference between 10-15 year outcomes and 20-30 year outcomes is important; abnormalities in diastolic relaxation will likely become clinically manifest later, and 30-year RV vs LV data are not yet available
CHOP data showed no difference in outcomes in the first 10 years after Fontan between hypoplastic left heart syndrome and systemic left ventricle patients
Boston data showed patients born with systemic left ventricle with normally related great vessels or single right ventricle do better than all other diagnoses
Melbourne group data showed right ventricular dominance is a risk factor if present at birth, but after surviving the first couple of years post-Fontan, survival curves are essentially identical regardless of ventricular morphology
Force-frequency relationships in systemic right and left ventricles in univentricular circulation outperformed normal ventricles
End-systolic elastance in Fontan patients is orders of magnitude higher than normals and even greater than in systemic right ventricle of Mustard patients
MRI tagging showed some segments of Fontan ventricular wall were 180 degrees out of phase with other parts, in systole when rest of ventricle was in diastole
Eight-year follow-up of Fontan patients showed maintained incoordinate relaxation, shortened IVRT suggesting rising left atrial pressure, and faster E wave deceleration suggesting falling compliance
Diastolic compliance of Fontan ventricles (predominantly left ventricles) is highly abnormal, unlike Mustard systemic right ventricles where diastolic compliance is not a problem
PHN data at 10-12 years post-Fontan showed systemic right ventricles had far more patients with increased E/E' ratio (indicating increased stiffness) compared to systemic left ventricles
Recent conductance catheter work from the Netherlands shows a tight relationship between arterial elastance and ventricular end-diastolic pressure