Ventricular dysfunction

Ventricular dysfunction is common in congenital heart disease patients. It causes 45% of deaths [16]. It is linked to several phenomena.
 

Ventricular function is deteriorated to a greater or lesser extent by all congenital heart diseases except ASDs, simple VSDs and patent ductus arteriosus on which surgery is performed in the first years of life. Even if malformations are anatomically corrected, the ventricles’ performance is not normalised, and more sophisticated tests than ejection fraction (EF) demonstrate that myocardial function is not optimal. Moreover, morphological modifications of ventricular chambers prevent the customary geometric approximations from being used to calculate EF. Systolic and diastolic dimension measurements offer the best means of assessment. The diameter thresholds for the LV are 2.5 cm/m² during systole and 4.5 cm/m² during diastole (short-axis view in echocardiography). As regards the RV, the complex shape of the ventricular chamber can only be correctly measured using the new 3D reconstruction technologies of MRI or echocardiography [5,6]. 

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 from birth (pulmonary stenosis, PAH) causes concentric hypertrophy rather than RV dilation. Right heart function remains adequate as long as intraventricular pressure is < 50% of left heart pressure and there is no associated volume overload (as in the onset of tricuspid insufficiency) [19]. However, its ability to compensate is lost within a period of ten to thirty years. When it functions as a systemic ventricle (hypoplastic LV, transposition of the great arteries), the RV fails over the course of the second or third decade if no surgical correction is performed. No medical treatment offers long-term efficacy for right-sided failure in congenital heart disease patients [14,17]. Consequently, treatment of RV failure requires polypharmacy (Table 15.7) [8].

Post-CPB, right ventricular dysfunction can be very severe in complex heart disease cases. In most cases, combinations of dobutamine and norepinephrin prove insufficient. A combination of milrinone and epinephrin is usually the only effective solution, supplemented by a vasoconstrictor (norepinephrin, vasopressin), with levosimandan as a relay therapy if required. However, levosimandan requires several hours to take effect and therefore must be initiated at induction [15]. 
 

 

Ventricular dysfunction

The ventricular function of congenital heart disease patients can never be considered as normal, excluding those with ASDs, small VSDs and patent ductus arteriosus operated on in infancy. Lack of reserve and ventricular dysfunction or failure are linked to several phenomena:     - Anatomical remodelling, palliative procedure      - Subaortic (systemic) RV, single ventricle     - Prolonged duration of life before correction     - Pressure overload, less well tolerated than volume overload     - Cyanosis     - Chronic ischaemia Right-sided failure is more common than LV failure among congenital heart disease patients. It is also more difficult to manage.

Arrhythmias

Compromising arrhythmias are very common in grown-up congenital heart patients, accounting for over half of all admissions for emergency hospital care and 20% of deaths [9,17]. The main independent risk factors are dysfunction of the systemic ventricle (EF < 30%), RV dilation, widening of QRS (> 180ms), surgical incisions on the cardiac walls, and advanced age (> 20 years) at the time of surgery [2,17]. The prevalence of arrhythmia increases with age: it is 38% > 50 years [3]. Arrhythmias double the risk of complications and increase mortality by 50% [3]. They may be an inherent feature of the patient’s malformation: Wolff-Parkinson-White syndrome in Ebstein anomalies, AV block in AV canal defects, ventricular tachycardia in tetralogy of Fallot and TGA. Some patients have two atrioventricular nodes. Arrhythmias may also be secondary to surgery, e.g. AV block after perimembranous VSD correction and supraventricular tachyarrhythmias following ASD correction and Fontan or Senning procedures [18]. Atrial tachyarrhythmias are common in patients who have distended atria, and bundle branch blocks in those with ventricular hypertrophy. In AF, scores such as CHA₂DS₂-VASc are not effective for congenital heart disease patients whose thromboembolic risk is linked more to the complexity and severity of the heart disease [10].

Reentry arrhythmias are resistant to drug treatments and require ablation of the anomalous bundles. This can be difficult if the patient’s anatomy is highly modified [12]. Ventricular tachycardia can occur in all pathologies, but is especially common in corrected Fallot patients who develop pulmonary insufficiency and RV dilatation [7]. The sudden death rate is higher than in the normal population. It increases by 2-5% per decade [1,18]. Diseases with the highest risk of sudden death are tetralogy of Fallot, aortic stenosis, univentricular heart, TGA and corrected TGA. Arrhythmias occurring during surgery must be treated aggressively from the outset, since they have a strong tendency to deteriorate into malignant arrhythmias. At-risk patients must be equipped with defibrillator patches, which must be attached prior to induction.
 
It is not uncommon for pacemakers and/or defibrillators to be implanted in these patients. Unfortunately, endovenous placement of electrodes is often impossible due to anatomical modifications linked to their malformations. Therefore, epicardial electrodes are often used. These must be implanted by sternotomy under general anaesthesia [20]. In cases of residual R-to-L shunting, the presence of intracardiac electrodes justifies systemic anticoagulation [2].

 

Arrhythmias

Arrhythmias are common and responsible for approximately 20% of deaths. Several risk factors:     - Severe dysfunction of the systemic ventricle (EF > 30%)     - Dilation of the RV     - Atriotomy or ventriculotomy, presence of intracardiac patches     - Age > 20 years at the time of surgical correction     - Widened QRS

Respiratory dysfunction

Grown-up congenital heart patients exhibit abnormal static pulmonary function compared to that of individuals of the same age, but their pathologies affect gas exchange [13]. 
 

• In the event of L-to-R shunting, compliance is reduced since the intrapulmonary blood volume is high. Work of breathing is increased. 
• In the event of R-to-L shunting, blood bypassing the lungs equates to an increase in the venous mixture (dead-space effect) [11]. End tidal capnography (ETCO₂) therefore gives an underestimation of actual PaCO₂. These patients hyperventilate chronically to compensate for low CO₂ clearance. While their response to hypercapnia is normal, their hypoxaemic response is significantly reduced [4]. 
• When arterial desaturation is caused by a shunt, the increase in FiO₂ has little influence on SaO₂.

Added to this are potential sequelae of previous cardiac surgery and skeletal deformities due to associated anomalies (e.g. scoliosis).


 

Gas exchange

Congenital heart diseases affect gas exchange:     - L-to-R shunt: reduced compliance     - R-to-L shunt: dead-space effect – ETCO2 measurements underestimate PaCO2      - Desaturation due to a shunt is not corrected by FiO2

© BETTEX D, CHASSOT PG, January 2008, last update May 2018



References