12-lead ECG of a patient with significant pulmonary stenosis. There is a right bundle branch block, evidence of RV hypertrophy and a slightly peaked P wave
Echocardiography is the diagnostic tool of choice (Fig. 18.2). It morphologically classifies the different types and locations of PS, evaluates the hemodynamic implications and delineates coexisting lesions. Doppler echocardiography provides the gradient across the obstruction, the presence and severity of pulmonary and tricuspid regurgitation and an estimate of the RV systolic pressure. Pressure gradients depend on the amount of flow across PV, the RV function and the pulmonary artery pressure. Care therefore needs to be taken in assessing the degree of stenosis. During pregnancy one would expect the pressure gradient to increase as flow increases. PS is considered mild when the peak gradient across the obstruction is <36 mmHg (peak velocity <3 m/s), moderate from 36 to 64 mmHg (peak velocity 3–4 m/s) and severe when the gradient is >64 mmHg (peak velocity>4 m/s). These gradients are often a little higher than invasive gradients but correlate well with catheter-based measurements (Fig. 18.3) [12–14]. Although it has limitations, echo is highly effective in tracking RV function, RV hypertrophy and an estimate of RV volume. In addition right atrial size and surrogates of RA pressure are easily measured and can be followed throughout a pregnancy. The key to maternal outcome is RV function, and caution should be exercised in simply relying on the pulmonary stenosis gradient to monitor antenatal progress. Indeed failure of the pressure gradient to rise is not reassuring but may indicate issues regarding the RV function.
Echo Doppler of a patient with significant pulmonary stenosis. The peak gradient across the valve is 78 mmHg with a mean gradient of 50 mmHg
Angiogram of a patient with severe pulmonary stenosis pre-balloon angioplasty. (a) Dilated main pulmonary artery. (b) Stenosis at the valve level. (c) Secondary infundibular stenosis. (d) Hypertrophied and trabeculated right ventricle
18.1.6 Other Diagnostic Tests
Clinical examination, ECG and echo are usually sufficient to assess a patient either before or during a pregnancy. However, other diagnostics may be useful especially in the more complex patients. Cardiac MRI provides additional information regarding anatomy of the RVOT and pulmonary artery. It can determine the exact location of PS and so can distinguish between PS at different levels. It is also the technique of choice for quantifying pulmonary regurgitation and right heart volumes, mass and function . Neurohormones, such as N-terminal pro-BNP, may be useful in pre-pregnancy risk stratification and, in high-risk patients, in tracking progress during pregnancy . Preconception cardiopulmonary exercise testing with measurements of peak oxygen consumption is useful for assessing the impact of an increased haemodynamic burden and in flagging those at increased risk of adverse maternal events .
18.2 Pregnancy Outcomes
18.2.1 Maternal Outcomes
Isolated PS is rarely a significant impediment to a successful pregnancy. Hameed et al. reported a small study of 17 pregnancies. The majority were asymptomatic throughout pregnancy, and there were no important maternal complications, regardless of the severity of PS . In a larger study of congenital heart disease pregnancies, Drenthen et al. reported the outcomes of 148 women with pulmonary stenosis. In this cohort three patients developed arrhythmia, one heart failure and three other cardiovascular complications. In the total cohort of 1,802 pregnancies, a pulmonary outflow tract gradient of greater than 50 mmHg was not associated with a significant increase in risk. The presence of cyanosis or sub-pulmonary atrioventricular valve regurgitation was, however, associated with an increased risk . As mentioned above severe PR is an independent predictor of complications especially if RV-impaired function coexists.
18.2.2 Fetal Outcomes
In general fetal outcomes are very good. The only caveats to this would be if there was significant cyanosis or very impaired maternal cardiac output. The recurrence risk for isolated PS is low in the region of 2–3 %. However, in syndromic patients and those with a dysplastic valve, genetic advice should be sought prior to conception as some of these conditions have an autosomal dominant pattern of inheritance.
18.3.1 Antenatal Monitoring
In patients with mild isolated PS, antenatal care will be very similar to routine antenatal care. Patients should be offered fetal echocardiography although pulmonary stenosis is often not detected until late in pregnancy or postdelivery. Patients with more severe disease or adverse risk factors will require serial assessment by a specialist cardiac-obstetric team. Regular clinical examination, ECG and echo testing will be required. The frequency of this will be proportionate to the degree of cardiac impairment. During a pregnancy one would expect the Doppler echo gradient to increase across the valve. Heart rate will start to rise from early in the first trimester, and cyanosis may worsen as the systemic vascular resistance drops.
Isolated PS at valve level is often responsive to balloon dilation. However it is rare that this is required in pregnancy and should not be embarked upon lightly. An increasing gradient per se is not a good indication for an invasive procedure that may involve ionizing radiation and possible a general anaesthetic. Intervention should be reserved for situations where delivery is not ideal (due to extreme prematurity) and where there is evidence of decompensation. Worsening cyanosis, ischaemia, chest pain and ventricular arrhythmias should trigger a discussion regarding balloon dilatation. Pulmonary stenosis in association with impaired RV function would also be concerning. Bed rest and low-dose diuretics may buy some time when planning optimal care. If intervention is planned during pregnancy, an obstetric team should be available in case the procedure triggers threatened preterm delivery. Techniques to minimize fetal morbidity associated with invasive procedures are well recognized , and fetal monitoring should be clearly documented.
In the very rare setting of the need for cardiac surgery during pregnancy, the women should be fully counselled regarding the risk of fetal loss which is still in the region of about 10 % despite protocols to optimal care and minimize fetal morbidity.
In general mode and technique of delivery will be dictated by obstetric factors. Chapter 6 outlines the generic principles. In patients who are at the more severe end of the PS spectrum, especially those with associated lesions, delivery may be challenging. Optimal right heart filling pressures need to be considered, and there is a role for measuring the central venous pressure directly. Arrhythmias should be treated promptly, and meticulous care should be taken regarding fluid balance. Bleeding or drugs that cause marked venous dilatation may be poorly tolerated. If there is marked RV hypertrophy, underfilling or prolonged pushing during the second stage may destabilize the patient. In patients with significant PS, slow incremental epidural anaesthesia can be used, but again care needs to be taken to avoid a precipitous drop in the venous filling pressures. In patients with an associated intracardiac shunt, such as a PFO or small atrial septal defect, the degree of cyanosis will be dependent on the balance between the right heart pressures and the left heart pressures. Increase in right heart pressures due to, for example, a heart rate-related dynamic outflow tract gradient or a drop in left heart pressures due to systemic vasodilatation will lead to increasing cyanosis. In extreme cases this can lead to ventricular ischaemia and further worsening of haemodynamics. There is also a risk of paradoxical embolism. In the absence of previous valve surgery or complicating issues, antibiotics are not usually given peri-delivery for endocarditis prevention. For the complex patients, a detailed delivery plan should be agreed in advance with input from the multidisciplinary cardiac-obstetric team.