Generally speaking, anatomical anomalies, chamber remodelling and abnormal haemodynamic conditions limit the ventricles’ functional capacity. Many features are involved: pressure or volume overload, structural anomaly (non-compaction, former ventriculotomy), anatomic abnormality, single ventricle, RV functioning as systemic ventricle, cyanosis, tachyarrhythmia, ischaemic suffering [3]. Heart failure is common in adult congenital heart disease patients (20-40% of cases). It causes 45% of deaths [13]. Nevertheless, the diagnosis is grossly underevaluated by the clinical symptomatology, since these patients are accustomed to limit their physical performance [8].

The relatively simple shape of the LV allows for a fairly accurate quantitative assessment of its function by means of echocardiography. The situation is different for the RV, whose complex morphology and significant remodelling in congenital heart disease patients exclude the use of geometric approximations that are applicable to the LV. RV anatomy and function can be most effectively assessed by MRI, to which a multislice CT scan and 3D echocardiography are useful alternatives [6]. Raised NT-proBNP (33-75 pmol/L) is a good marker of the risk of ventricular failure and death (OR 9.05-16.0) [1].

Left ventricle

An increase in afterload (aortic stenosis, coarctation) leads to concentric hypertrophy that may be massive. However, this ventricle exhibits functional decline per unit of mass even if it is capable of generating high pressure. Volume overload causes dilated hypertrophy of the LV, which can accommodate an increase in end-diastolic volume of approximately 40%. However, the efficiency of such a LV is diminished, as it is working over a large diameter (LaPlace’s law) and becomes very sensitive to any increase in afterload. 

LV function is impaired by the anatomical anomaly that changes its shape, generally making it more spherical. LV function is also modified by cyanosis and hypoxaemia in proportion to their intensity and duration if corrected late. In single ventricle (SV) defects, function is less impaired if the SV is anatomically of a left type. If it is of a right type, the ventricle’s performance rapidly becomes deficient. Under all these conditions, the echocardiographic ejection fraction (EF) has little validity for defining LV performance, since the geometric and hemodynamic assumptions on which this is based are inapplicable in the event of such changes. Tissue Doppler and speckle-tracking echocardiography, as well as cardiac MRI, are a better examination for this purpose, due to their ability to measure systolic deformation and ventricular volumes.

The usual medical treatment of cardiac failure (converting-enzyme inhibitors, beta-blocker, spironolactone) is generally efficient, but the decrease in LV afterload induces a systemic vasodilatation which favors a R-to-L shunt in case of mixed or cyanotic shunt. Resynchonisation therapy with a pace-maker is rarely efficient because of the abnormal morphology of the ventricles [3].

Right ventricle

In congenital heart disease patients, heart failure most commonly affects the right ventricle. Volume overload (ASD, major tricuspid or pulmonary insufficiency) causes eccentric hypertrophy and dilation of the RV. It is well tolerated for a long time, but entails a high risk of refractory ventricular arrhythmia [6]. A chronic increase in afterload (pulmonary stenosis, pulmonary hypertension, RV in systemic position) causes concentric hypertrophy rather than dilation. Right heart function remains adequate as long as intraventricular pressure is < 50% of left heart pressure and there is no associated volume overload. Patients become symptomatic if RV pressure exceeds half of systemic pressure or if tricuspid insufficiency occurs [2,15]. When subjected from birth to high afterload, the RV retains its foetal configuration, does not thin, and keeps the same wall thickness as the LV. It may function in this way for several decades. As a result, the prognosis for congenital pulmonary hypertension (PHT) is much better than for PHT occurring later in adult life, since it is dependent on right heart function [10]. When adapting to high afterload, the RV resembles the LV since its hypertrophy mainly affects the circular myocardial fibres. In such instances, circular contraction exceeds longitudinal contraction, as in the LV, although contrary to a normal RV. However, systolic torsion is absent [11]. Nevertheless, its ability to compensate is gradually overcome – the RV dilates and is subjected to frequent ventricular arrhythmias. If it is functioning as a systemic ventricle, as is the case in 12% of congenital heart diseases (hypoplastic LV, double-outlet RV, transposition of the great arteries), the RV fails over the course of the second or third decade of life if no surgical correction is performed [2]. Such correction will not ensure adequate functional recovery if the size of the RV is > 150 mL/m2 [15]. No medical treatment offers long-term efficacy for right-sided failure in congenital heart disease patients [12,14].

RV performance is highly dependent on that of the LV, since the LV contributes > 40% to right-sided ejection through the contraction of the interventricular septum, which belongs physiologically to the LV. This support is lost in the event of a wide VSD, left-sided hypoplasia or major remodelling of the left chambers [7]. Moreover, dilation of the RV by volume overload, as in the case of a wide ASD, pushes the septum back inside the LV during diastole and limits its filling. If PHT is added to this situation, septal swing also takes place during systole. In addition, the duration of RV systolic ejection is extended if right-sided afterload is high, and the peaks in systolic pressure desynchronise between the two ventricles. In this situation, a rise in left-sided afterload has two benefits: it increases LV contractility by Anrep effect, and places the septum back in a position in which it curves to the right by increasing left-sided intraventricular pressure. Correcting the position of the septum also limits dilation of the tricuspid annulus and reduces the degree of tricuspid insufficiency [7]. Hence the efficacy of systemic vasoconstriction (raising SVR) in the management of right-sided failure.

Systemic vasoconstrictors also increase right coronary perfusion pressure. Indeed, the risk of RV myocardial ischaemia increases as PAP rises, since coronary perfusion of the RV is systolic and diastolic, while it is mainly diastolic for the LV. Although systemic diastolic pressure remains higher than pulmonary diastolic pressure, the reduced gap between the two systolic pressures in the case of severe PHT lowers the coronary perfusion pressure of the RV by reducing its systolic component. With almost half of its O₂ supply removed, right-side coronary perfusion predominates during diastole and is therefore similar to that of the LV [5]. The hypertrophied RV is thus prone to ischaemia as soon as systemic AP drops, for instance in cases of perioperative hypovolaemia. Moreover, the coronary blood flow reserve in the event of increased O₂ requirement is reduced in cases of right-sided hypertrophy, where the capillary density per unit of mass is lower than in a normal ventricle [2,5].

Ventricular assist devices (VAD) and transplantation

Patients with congenital heart disease suffer from many unfavourable characteristics for implantation of an assist device or a heart transplant: anatomical complexity, abnormal size and position of vessels or cardiac chambers, multiple previous operations, palliative corrections, pulmonary hypertension, cyanosis, allosensibilization and high level of preformed antibodies (transfusions, homografts, etc) [8]. They are on average 15 years younger than other candidates. Half of them are suffering from a single ventricle or a Fontan failure; less frequent are naturally or surgically corrected transposition of great arteries, and cases of RV in systemic position. Their waiting time before transplant is longer than usual because of their multi-sensitization and the requirement of a donor with sufficient length of the great vessels. Technically, canulation is arduous, dissection is haemorrhagic, and RV failure is frequent due to pulmonary hypertension. Cyanosis, hepatic dysfunction and exsudative enteropathy further exacerbate the risk of bleeding. Possible aorto-pulmonary collaterals maintain a high-output cardiac failure [8].

Under VAD, the 1-year survival rate is only 52% for adult congenitals [4]. Their perioperative mortality after transplantation is higher than in case of cardiomyopathy (20% versus 9% at 1 month), but their long-term survival rate is identical (50-60% at 10 years) [9].


 

Ventricular function

In general, adult congenital heart disease patients’ ventricular function is diminished due to malformation, loading anomalies, remodelling and cyanosis. Right-sided failure is more common than LV failure among congenital heart disease patients

© BETTEX D, CHASSOT PG, January 2008, last update February 2020



References