Acute MI Rates on the Rise Among Pregnant Women in the US

Although rare, having an acute MI during or shortly after pregnancy carries an unusually high in-hospital mortality rate of 4.5%, researchers say.

Acute MI Rates on the Rise Among Pregnant Women in the US

Women in the United States are increasingly at risk for acute MI during pregnancy, labor and delivery, or the 2 months after giving birth, according to an analysis of data spanning from 2002 to 2014. While cases are few and far between, when pregnancy-related acute MI does occur, it carries a high in-hospital mortality rate and merits careful management, investigators of the new study say.

“Hormonal and hemodynamic changes in the cardiovascular system and the hypercoagulable state of pregnancy in part account for the increased risk of AMI during pregnancy, which occurs with a frequency approximately three- to fourfold higher than that for nonpregnant women of childbearing age,” write researchers led by Nathaniel R. Smilowitz, MD (New York University School of Medicine, NY). Previous population-based studies have identified higher age, hypertension, diabetes, and thrombophilia as factors that independently predict acute MI risk among pregnant women, they add, but data are slim on contemporary management of the condition.

Indeed, pregnancy-related acute MI is a “rare event,” Sripal Bangalore, MD (New York University School of Medicine), the study’s senior author, told TCTMD. “It’s not going to be very frequent, but if you do see it it’s important to recognize that the mortality rate is actually higher” than what would normally be expected with acute MI, he stressed.

Management of these cases is unique, Bangalore pointed out, in that treating pregnant or recently pregnant women with dual antiplatelet therapy or an anticoagulant “is challenging with all the bleeding issues surrounding labor and delivery and so forth. Also, you have to be cognizant of the fact that many of the medications we use normally for treating AMI patients will have contraindications for lactating mothers.”

What with the complexity, “early recognition and a team approach, working closely with the OB, is important to better treat these patients,” Bangalore said.

Mortality Rate ‘Not Trivial’

For their study,   recently published online in Mayo Clinic Proceedings, Bangalore and colleagues looked at numbers from the National Inpatient Sample on more than 55 million pregnancy-related hospitalizations occurring between 2002 and 2014. There were 4,471 acute MIs, amounting to approximately one out of every 12,440 hospitalizations and an estimated 8.1 cases per 100,000 hospitalizations. Most (53.5%) occurred in the postpartum period, with the rest during labor and delivery (23.7%) or beforehand (20.6%).

Slightly more than half of the events were NSTEMI (57.6%) and the rest STEMI. In all, 6.5% of women were in cardiogenic shock, and 2.9% had Takotsubo syndrome. Compared with women who did not have acute MI, those who did tended to be older (mean age 33.1 vs 28.0 years; P < 0.001) and to have more cardiovascular comorbidities.

Coronary artery dissection was documented in 14.5% of cases, seen in 23.1% of women diagnosed with STEMI and 8.2% of those with NSTEMI. Nearly one-quarter of patients who ultimately underwent invasive management had coronary dissection.

“Substantial increases in the circulating sex hormones estrogen and progesterone, changes in hemodynamics, hemodilution, and increases in cardiac output during pregnancy can lead to progressive connective tissue weakening, increased vascular shear stress, and spontaneous coronary artery dissection (SCAD),” the researchers explain.

Previous studies have shown a SCAD rate of up to 40% among pregnant women with acute MI, and as such the condition is often considered a “key etiology” of acute MI in this setting, they point out. “The modest frequency of SCAD in the present analysis may reflect underrecognition or undercoding of this important diagnosis. Therefore, the true incidence and outcomes of SCAD during pregnancy warrant further exploration.”

Additionally, gestational diabetes and preeclampsia each were linked to increased risk of acute MI. Independent predictors of acute MI during pregnancy were older age, tobacco use, hypertension, dyslipidemia, diabetes, known heart failure, anemia, and malignancy. Also, the proportion of women who had acute MI was much higher among patients with any preexisting risk factor for CAD, such as tobacco use, hypertension, dyslipidemia, diabetes, or renal impairment, than among those without a risk factor (66.1 cases vs 5.2 cases per 100,000 hospitalizations). Still, 61% of acute MIs happened in patients lacking CAD risk factors.

Over time, the rate of pregnancy-related acute MI rose: from 7.1 cases per 100,000 hospitalizations in 2002 to 9.5 cases per 100,000 hospitalizations in 2013 (P < 0.001 for trend). With adjustment, the odds ratio for acute MI was 1.25 (95% CI 1.02-1.52) for 2014 versus 2002.

There are several hypotheses for why acute MI is on the rise in this population, but it likely relates to women becoming pregnant at older ages and having more CV risk factors than in the past, Bangalore noted to TCTMD. Women’s mean age at the time of hospitalization for labor and delivery increased from 27.9 years in 2002-2003 to 28.3 years in 2012-2013 (P < 0.001).

Invasive management was pursued in 53.1% of women who had pregnancy-related MI, with one-quarter undergoing coronary revascularization. The risk of in-hospital mortality was nearly 40-fold higher with versus without acute MI (adjusted OR 39.9; 95% CI 23.3-68.4), occurring at a rate of 4.5% among women who had an acute MI during or shortly after pregnancy.

“Despite contemporary management strategies, maternal mortality rates remained high,” the investigators conclude.

Bangalore said it’s important for clinicians to know that acute MI can happen in this context. “If you’re not aware that a pregnant patient can have an MI, it’s easy for cardiologists to say, ‘Oh, it’s not an MI. It may be X, Y, and Z.’ So having that index of suspicion is important, and also taking [these events] seriously,” he advised. “The mortality rate of 4.5% in the hospital is not trivial for a young cohort such as this.”

Caitlin E. Cox is News Editor of TCTMD and Associate Director, Editorial Content at the Cardiovascular Research Foundation. She produces the…

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  • The work was supported by an award from the National Heart, Lung, and Blood Institute of the National Institutes of Health.
  • Smilowitz and Bangalore report no relevant conflicts of interest.