Chapter 37 – Cardiac Surgery during Pregnancy

Abstract

Cardiac disease has been the leading cause of overall maternal mortality in the UK since the 2002–2004 triennium. The maternal death rate from cardiac disease has increased from 1.65 per 100,000 maternities in the 1997–1999 triennium to 2.34 per 100,000 maternities in the 2013–2015 triennium. This is thought to be due to increasing maternal age, increasing levels of obesity and better recognition of cardiac pathology at autopsy.

Chapter 37 Cardiac Surgery during Pregnancy

Savio J. M. Law and Sarah E. Round

Background

The cardiac diagnoses from the women who died in 2009–2014 are shown in Table 37.1. Sudden arrhythmic cardiac death with a morphologically normal heart was the most common cause for death (31% of women who died from cardiac causes). This was followed by ischaemic deaths (22%), myocardial disease/cardiomyopathy (18%), and aortic dissection (14%).

Table 37.1 Sub-classification of cardiac deaths for whom information was available for an in-depth review (UK and Ireland, 2009–2014). (Reproduced with permission of Knight et al., 2016)

Sub-classification	Number of deaths	Percentage of total (n = 153)*
Sudden arrhythmic cardiac death with a morphologically normal heart	47	31
Ischaemic deaths Atherosclerosis (16), coronary dissection (11), other (7)	34	22
Myocardial disease/cardiomyopathy Dilated cardiomyopathy (4), LV hypertrophy with or without fibrosis (5), obesity cardiomyopathy (2), myocarditis (3), peripartum cardiomyopathy (9), hypertrophic obstructive cardiomyopathy (1), arrhythmogenic RV cardiomyopathy (2), other ventricular disease (1)	27	18
Aortic dissection	21	14
Valvular heart disease Valve disease (9), endocarditis (2)	11	7
Others Pulmonary arterial hypertension (6), undetermined cardiovascular disease (1)	7	5
Essential hypertension	6	4
TOTAL	153

* Excludes 36 late cardiac deaths for which no information was available.

Several key areas for improvement have been identified in the recent review of maternal deaths due to cardiac disease. Pre-pregnancy counselling of women of child-bearing age with known cardiac disease is lacking and is a sensitive subject that is rarely broached by clinicians. Frequently, transitions from paediatric to adult cardiology services and massive changes in life circumstances at this age result in a lack or loss of follow-up. Logistical problems, such as the lack of co-location of obstetric and cardiac services, and the lack of access to cardiac investigations still need to be improved. In this high-risk maternity population, the management of signs and symptoms suggestive of cardiorespiratory compromise should focus on making a diagnosis, rather than simply excluding a life-threatening diagnosis. In such circumstances, pregnancy or breast-feeding should not be the reason for failing to instigate potentially life-saving investigations or treatment.

Physiological Changes of Pregnancy

A number of the normal physiological changes cause exacerbation of coexisting cardiac disease (Box 37.1). The most significant changes are a 40% increase in intravascular volume by 32 weeks and a 40% increase in the CO. The CO increases further during labour and reaches its maximum immediately after delivery due to autotransfusion from the uterus and removal of the aortocaval compression by the foetus. These changes can lead to decompensation around the time of delivery and immediately afterwards.

Box 37.1 Normal physiological changes associated with pregnancy

Circulating volume
- Blood volume ↑ 30-40%
- Physiological anaemia (plasma ↑ 45%/erythrocytes ↑ 20%)
- ↓↓ Colloid osmotic pressure ⇒ ↑ risk of pulmonary oedema
- Altered plasma protein binding of drugs
- Neutrophilia
- Hypercoagulable state
Cardiovascular
- ↑ Sympathetic tone ⇒ SV ↑ 30% + HR ↑ 15% ⇒ CO ↑ 50%
- ↑ Wall stress/contractility ➔ ↑ Myocardial O₂ consumption
- CVP and PAWP unchanged (PVR and SVR ↓ 20%)
- Systolic BP – unchanged
- Diastolic BP – initially falls and then returns to normal at term
- Aortocaval compression ⇒ ↓↓ CO
- Increased vascularity of airway – especially nasal passages
Respiratory
- Diaphragmatic splinting
- ↑ Minute ventilation, ↑ RR, ↑ V_T ↓ functional respiratory capacity
- ↓ PaCO₂, ↓ HCO₃^–, ↓ buffering capacity
- Total body O₂ consumption ↑ 15–20%
Gastrointestinal
- Delayed gastric emptying, constipation
- Increased risk of gastro-oesophageal reflux
Genitourinary
- ↑ Renal blood flow and GFR
- Increased risk of vesico-ureteric reflux/infection
- Glycosuria (tubular transport maximum exceeded)
- Proteinuria (up to 0.3 g d^–1)
Metabolic & Endocrine
- ↑↑ Prolactin, adrenocorticotrophic hormone, cortisol
- ↓ Growth hormone
- ↑ Thyroid-binding globulin, T₄ and T₃ (free-T₄ near normal)
- ↑ Gastrin

Twenty-one per cent of maternal deaths occur on the day of delivery, while more than half of total maternal deaths due to cardiac causes occur during the period of the day of delivery to 42 days after delivery (Table 37.2).

Table 37.2 Timing of maternal deaths due to cardiac causes in relation to pregnancy. (UK and Ireland, 2009-2014). (Reproduced with permission from Knight et al., 2016)

Time period of deaths in the pregnancy care pathway	Total (n = 153)* (frequency, %)
Antenatal period/still pregnant	24 (15)
Postnatal on day of delivery	32 (21)
Postnatal 1–42 days after delivery	52 (34)
Postnatal 43–91 days after delivery	18 (12)
Postnatal 92–182 days after delivery	12 (8)
Postnatal 183–273 days after delivery	9 (6)
Postnatal 274–364 days after delivery	6 (4)