Heart disease is the world’s leading killer, in both men and women. A recent study, which harnessed a new technology with “unprecedented capabilities,” brings us one step closer to understanding how men and women's hearts operate distinctly. It's a breakthrough that could save lives because of its illumination of a crucial difference between male and female hearts.

Scientists have long known that women’s hearts are smaller and beat faster, on average, than men’s. But according to this new research, men and women have dramatically different blood flow patterns in their hearts, too. Understanding this difference could lead to better ways of identifying heart disease across sexes.

According to the study — which analyzed the blood flow patterns of 39 young, healthy people — women’s blood swirls more than men’s as it moves through the heart and they experience more strain in the heart's a left ventricle. In contrast, men had higher kinetic energy (the blood's momentum) in the left ventricle, the heart’s main pumping chamber.

"There may be inherent differences in the cardiac performance of young men and women, and we expect these differences are normal and healthy," David Rutkowski, lead author on the study and researcher at the University of Wisconsin in Madison, tells Inverse.

"By observing these differences, we demonstrated the increased sensitivity that 4D flow MRI and cardiac strain analysis can provide over current standard clinical measurements."

This small study is a preliminary one. But if it is replicated in a larger number of subjects and in people with heart disease, this new approach to analyzing cardiac function could help physicians of the future better diagnose and track the progression of heart disease, Rutkowski says.

The study was published Thursday in the journal Radiology: Cardiothoracic Imaging.

Glimpsing the impossible

To get a closer look at the heart’s blood flow than ever before, the research team used a sophisticated imaging technique called four-dimensional (4D) flow MRI. In real-time, the 4D flow MRI documents blood’s turns, twists, and speed as it moves through the heart. The approach provided results that "could not otherwise be obtained with standard clinical measurements," Rutkowski says.

A) A 4D flow MRI scan shows how kinetic energy varied in the left and right ventricles. B) Blood flow speed through the pulmonary artery and ascending aorta. Radiological Society of North America

To test whether blood flow varied by sex, researchers recruited 20 healthy men and 19 healthy women between 20 and 35-years-old to complete 4D flow MRI scans and 2D MRI scans. In just eleven minutes, researchers got a relatively advanced picture of cardiac function through the 4D MRI scans. The team looked at a variety of blood flow characteristics in the left ventricle and saw some stark sex-based differences:

Kinetic energy (the blood's momentum, which signals how efficiently the heart is working) was higher in men than women.

(the blood's momentum, which signals how efficiently the heart is working) was higher in men than women. Vorticity (how the blood rotates and swirls in the left ventricle) was higher in women than men.

(how the blood rotates and swirls in the left ventricle) was higher in women than men. Strain (how the muscle tissue of the heart contracts) was higher in women than men.

4D flow MRI scans were used to generate visualizations of blood flow through the left ventricle. The technology helped researchers discover exactly how fast, and in which direction, blood flowed. Radiological Society of North America

Staying heart-healthy

This study, which didn't focus on specific diseases, focused on providing a "preliminary baseline for 'normal' flow in men and women," Rutkowski says. An exact definition "normal" in regards to blood flow in the heart and how that changes between men and women, hasn't been known before.

The sex-based differences seen in this study don't indicate any clear advantages to having a man's heart over a woman's — and the team doesn't know what causes these differences yet. More research, potentially using 4D flow MRIs, may help us understand the cardiac performance mystery, by sex.

For now, it's important for people to realize the symptoms of a heart attack that look different for men and women. While both genders are more likely to experience chest pain, pressure or discomfort, women are more likely to feel a sense of dread, dizziness, back pain, among other symptoms, while men are more likely to feel cold sweats and pain in their left arm. Across sexes, a nutritious diet, no smoking, and lots of physical activity can help keep hearts strong, regardless of gender.

Abstract:

Purpose: To further understand the relationship between cardiac function and flow, on the basis of sex, by quantifying cardiac flow characteristics and relating them to cardiac muscle performance in young adults.

Materials and Methods: In this cross-sectional study, cardiac four-dimensional flow MRI and two-dimensional cine MRI were performed in 20 male and 19 female volunteers aged 20–35 years. Velocity-based metrics of flow, kinetic energy (KE), vorticity, and efficiency indexes were quantified, as well as cardiac strain metrics.

Results: Peak systolic blood KE (men: 4.76 mJ ± 2.66 [standard deviation]; women: 3.36 mJ ± 1.43; P = .047) was significantly higher in the male left ventricle (LV) than in the female LV. Peak systolic vorticity index (men: 0.008 radian ∙ m2/mL ∙ sec ± 0.005; women: 0.014 radian ∙ m2/mL ∙ sec ± 0.007; P = .007), peak diastolic vorticity index (men: 0.007 radian ∙ m2/mL ∙ sec ± 0.006; women: 0.014 radian ∙ m2/mL ∙ sec ± 0.010; P = .015), and cycle-average vorticity (men: 0.006 radian/sec ± 0.001; women: 0.011 radian/sec ± 0.002; P = .001) were significantly higher in the LV of women than they were in the LV of men. Radial, circumferential, and long-axis strain metrics were significantly higher in the female LV than in the male LV (P < .05). Circumferential systolic and diastolic strain rates dis- played moderate correlation to peak systolic (r = −0.38; P = .022) and diastolic vorticity (r = 0.40; P = .015) values, respectively. Results are reported as mean ± standard deviation.

Conclusion: LV vorticity metrics were observed to be higher in women than in men and displayed moderate correlation to cardiac strain metrics. The methods and results of this study may be used to further understand the sex-based cardiac efficiency relationship between cardiac function and flow.