Magnesium? Winnie asked, keeping her tone as loose as an unwinding coil of slack line. Magnesium?
Yup. Magnesium, I repeated. One gram iv.
I caught her lingering look, but Winnie and I go back six years. Once she was sure I meant it, she produced the vial. One gram, coming up. Mrs. Wu, our elderly patient, had come in gasping for air. She had been shopping with her daughter when suddenly her legs lost power and her lungs grew tight. As soon as Mrs. Wu arrived, Winnie had put her on oxygen; now she seemed a little better. But she still clutched her daughter’s hand and kept up a steady singsong of Cantonese: Maybe Chinese medicine . . . I imagined her saying, then the daughter soothing, It’s the hospital. They know.
Mrs. Wu’s electrocardiogram—the tracing of electrical activity in the heart—looked like a Jackson Pollock. Instead of a smooth tracing bringing forth 80 beautifully spaced spikes a minute, it was spitting out a rapid-fire and asynchronous 140 spikes, or heartbeats, a minute. Mrs. Wu’s heart was creating a painting that already had a title: atrial fibrillation.
Our hearts have four chambers to handle the intricate job of replenishing oxygen-poor blood and pumping it out. While the right atrium and right ventricle pump oxygen-poor blood from the body out to the lungs, the left atrium and left ventricle receive oxygen-rich blood from the lungs and pump it to the rest of the body. The atria and ventricles must work together to achieve the split-second timing that allows the chambers of the heart to pump blood in and out some 60 to 100 times a minute, day in, day out. The atria set the rhythm for the muscular contractions we call the heartbeat, and the ventricles supply the horsepower.
