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Cardiac Surgery in Pregnancy

Kathryn Lindley

Cardiopulmonary bypass during pregnancy carries similar risk to the mother as their nonpregnant counterparts; however, fetal mortality remains high [1]. Fortunately, the need for cardiac surgery during pregnancy is relatively rare. However, with a growing number of women of childbearing age with congenital heart disease and underlying cardiovascular risk factors such as hypertension and diabetes, these numbers may increase in the future [2]. While most cardiovascular conditions can be adequately temporized with medical therapy throughout the pregnancy, there are a variety of conditions which may necessitate urgent or emergent surgery in a pregnant or immediately postpartum woman.

Cardiac Surgery during Pregnancy

Cardiac surgery during pregnancy carries the risk of morbidity and mortality for both the mother and the fetus. In the current era, maternal perioperative mortality is comparable to that in the nonpregnant women unless the surgery occurs in an emergent setting [3]. Though prior studies reported mortality between 3%–15%, current estimates of maternal mortality are approximately 5%–9% [4–6]. For women who undergo cardiac surgery immediately following cesarean delivery, additional blood products are often required during surgery, but excessive uterine bleeding is not typically reported [5]. Some of the common indications for cardiac surgery in pregnancy are reviewed in Table 19.1.

Valve Disease

While regurgitant valvular heart conditions are generally well tolerated during pregnancy, severe left-sided stenotic lesions may become symptomatic as the hemodynamic load of pregnancy increases throughout the second and third trimester. This is most commonly related to congenital heart defects such as bicuspid aortic valve or Shone complex, or rheumatic heart disease [7]. Severe prosthetic valve dysfunction may also present in this manner [8].

If the patient cannot be temporized with medical therapy or percutaneous interventions, surgery may be required to relieve symptomatic heart failure during pregnancy or the immediate postpartum period [7,9]. Mechanical heart valves require meticulous care throughout pregnancy to avoid thrombotic and bleeding complications. In the setting of mechanical valve thrombosis, emergent valve replacement may be required:

•If the patient is too unstable for or otherwise deemed not a candidate for thrombolysis [9]

Valvular endocarditis may also require surgical intervention during pregnancy in the setting of

•Large, mobile vegetations

•Recurrent embolic phenomena

•Severe valvular destruction causing heart failure

•Highly resistant organisms

•Abscess formation [9]

Aortopathies

Aortic enlargement, particularly in the setting of underlying connective tissue disorders such as Marfan syndrome, Loeys-Dietz syndrome, Ehlers-Danlos IV, Turner syndrome, coarctation of the aorta, and bicuspid aortic valve, can be associated with significant maternal morbidity and mortality [10]. These risks are further elevated among women with additional risk factors such as a family history of aortic dissection, hypertension, prior personal history of aortic dissection, and tobacco use. Patients with underlying aortopathy may require emergent aortic repair or replacement in the setting of an aortic dissection during pregnancy [10]. Semi-elective aortic root replacement may be undertaken in women with severely dilated aortic root discovered during pregnancy if termination is declined, or if progressive dilatation occurs during pregnancy [10].

Coronary Artery Bypass Grafting

Coronary artery dissection is the most common cause of myocardial infarction in pregnant and postpartum women [11]. This is most commonly managed conservatively [11]. However, in the setting of cardiogenic shock, such as in the setting of left main coronary artery dissection or mechanical complications of myocardial infarction, or after technical failure or complication of attempted percutaneous intervention, coronary artery bypass grafting may be elected [11].

While atherosclerotic coronary disease is less common among women of childbearing age, it may occur in women with risk factors such as diabetes, familial hyperlipidemia, hypertension, obesity, or tobacco use [12,13]. In the setting of coronary ischemia with severe three-vessel disease or high-risk features for percutaneous intervention, such as left main disease, surgical revascularization may be selected during pregnancy or immediately following delivery in select patients [12,14].

Surgery Timing

Preconception

Ideally, cardiovascular evaluation including imaging will occur prior to conception, and surgery may be considered at that time to potentially reduce the risk of cardiovascular complications of pregnancy [7]. This approach also reduces the potential risks of exposure to cardiopulmonary bypass to the fetus during pregnancy. However, prophylactic preconceptual surgery must be weighed against the intrinsic risks of the surgical procedure itself and the long-term sequelae of the surgery. For example, it is reasonable for preconceptual patients with asymptomatic severe aortic stenosis with aortic velocity ≥4.0 m/s or mean pressure gradient ≥40 mmHg to undergo prophylactic aortic valve replacement [9]. However, if a bioprosthetic valve is placed, the patient will inevitably require a repeat valve surgery in the future. If a mechanical valve is placed, the pregnancy will be complicated by anticoagulation management and the risk for warfarin embryopathy [7,10]. Preconceptual surgical intervention should be performed for symptomatic severe aortic or mitral stenosis [9].

Pre-pregnancy surgical intervention is also recommended for patients with aortopathy and Marfan or related disorders with ascending aorta size ≥45 mm [10]. For other patients, such as those with a bicuspid aorta, surgery should be performed when the aorta size is ≥50 mm [10]. For patients with Turner syndrome or an otherwise small body surface area, surgery should be done prior to pregnancy when the aorta exceeds ≥27 mm/m2 [10].

Pregnancy

If the patient is already pregnant and surgery is being contemplated, optimal timing of surgery presents challenges for both the mother and the fetus. Shared decision making in a multidisciplinary manner is preferred. Surgical decisions must be tailored to the specific needs of the patient based on the underlying lesion, maternal status, and the gestational age of the fetus. The best time period for cardiac surgery in pregnancy is between 13–28 weeks.

Role of the Multidisciplinary Team

The decision for cardiac surgery in pregnancy should always be made in the context of an experienced multidisciplinary team, including maternal-fetal medicine specialists, cardiologists, obstetric and cardiac anesthesiologists, cardiac surgeons, and neonatologists.

Timing of Surgery

The ideal surgical timing depends partially on the urgency of the procedure.

i.In the setting of life-threatening conditions requiring urgent surgical intervention, such as aortic dissection or mechanical valve thrombosis, surgery should be undertaken as soon as possible.

ii.For less urgent procedures, the procedure may be delayed for fetal benefit, as it has been shown that fetal mortality declines as gestational age progresses [15].

iii.Prior to fetal viability around 24 weeks’ gestation, preterm labor or delivery would lead to demise of the fetus, thus delay until closer to viability may be of some benefit for fetal survival. Subsequent to fetal viability, preterm labor or fetal distress requiring delivery will be associated with increased infant morbidity and mortality proportionate to degree of prematurity [16]. Thus, consequences of very premature birth must be considered in women undergoing cardiac surgery in the late second trimester.

iv.For patients in the third trimester, cesarean delivery immediately followed by initiation of cardiopulmonary bypass for cardiac surgery is usually the preferred strategy, as the fetus is typically developed well enough for reasonably good survival after delivery [5].

Maternal and Fetal Complications of Cardiac Surgery

Maternal complications are reported in 15% of patients, with persistent heart failure (6%), cardiac arrhythmia (2%), and postoperative bleeding (2%) being most common [4]. Maternal complications are higher in women undergoing urgent or emergent cardiac surgeries [4]. Fetal complications are reported in 12%, with respiratory distress syndrome (5%) and developmental delay (3%) being most common [4].

Risk of fetal demise related to cardiac surgery has been reported as between 14% and 33% [3–6]. The risk appears to be higher if there are additional maternal risk factors for fetal loss, or if the surgery occurs in an emergent setting or at an early gestational age [5]. Most of this risk is related to cardiopulmonary bypass, and not the anesthesia itself [5].

Cardiopulmonary Bypass in Pregnancy

Physiologic changes during cardiopulmonary bypass:

i.During cardiopulmonary bypass, there is a decrease in mean arterial blood pressure and flow pulsatility, which tends to decrease uteroplacental perfusion and may lead to onset of uterine contractions [5]. Uterine blood flow is not auto regulated, but depends entirely on maternal blood pressure and uterine vascular resistance [3]. Animal studies demonstrate that nonpulsatile flow leads to significant placental dysfunction due to severe vasoconstriction [3].

ii.Hypothermia increases the risk of fetal arrhythmias and acid−base imbalance [3].

iii.Both cooling and warming during cardiopulmonary bypass are also associated with sustained contractions [3]. The deeper the hypothermia, the greater the risk of fetal death [3].

Sustained contractions are the most common cause of fetal demise, which may occur after the conclusion of cardiopulmonary bypass and cardiac surgery [3,5]. Stillbirth and fetal demise have been reported to occur up to several days after surgery [5]. Sustained contractions lead to a reduction in uteroplacental blood flow, causing fetal hypoxia and subsequent fetal demise [3]. One proposed mechanism for this is dilution of progesterone in the setting of cardiopulmonary bypass, and post-cardiopulmonary bypass progesterone administration has been used to stop premature labor [3]. Reports of successful tocolysis with magnesium have also been reported [5].

Optimizing Fetal Outcomes during Cardiopulmonary Bypass

When possible, if surgery is not urgent, it should be delayed until the second trimester for women with early gestation pregnancies. For all pregnant women undergoing cardiac surgery, the following recommendations can help optimize fetal outcomes (Table 19.2). Maintenance of normothermia reduces fetal loss [3,5,17,18]. Attempts should be made to minimize blood loss and maintain normokalemia (<5 mmol/L) [5]. Avoid maternal hypoxemia and hypoglycemia to reduce the risk of fetal bradycardia [5,19,20]. Attempts should be made to minimize cardiopulmonary bypass times and maintain pulsatile flow, a high flow rate (>2.5 L/min/m2), and a mean arterial pressure >70–75 mmHg [5]. Blood pressure should ideally be managed via flow rates of cardiopulmonary bypass rather than through sympathomimetic drugs, though these can be used if needed, preferably phenylephrine and ephedrine [3,5]. Pregnancy is intrinsically a hypercoagulable state, so antifibrinolytic agents such as tranexamic acid should be limited to patients with concern for ongoing bleeding [5]. For women beyond 20 weeks’ gestational age, uterine displacement by placement in the left lateral recumbent position is recommended [5]. For women beyond 24 weeks gestational age, it is reasonable to administer preoperative steroid for fetal lung maturation [3]. Fetal heart rate monitoring is recommended, with adjustment in hemodynamics for a goal fetal heart rate of 110–160 bpm. Following surgery, continuous and frequent fetal monitoring is recommended due to the high risk of fetal demise in the early postoperative period [3]. Preoperative neonatology consultation is also advised, in the event of premature delivery.

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