It is true, and was the basis of Edison’s showmanship, that low-frequency alternating current can be more hazardous than an equivalent direct current. By oscillating at a similar (ie, close enough) frequency to the human heart, a sufficiently strong alternating current can cause that organ to beat arhythmically and thereby induce ventricular fibrillation—a potentially deadly condition that needs to be corrected immediately.
This is the improved, edited version. How can a journalist equate 50 to 60 Hz to be close to the frequency of the human heart 60 to 120 beats/minute (1 to 2 Hz).
With corrections like this, I remember why I stopped reading the Economist.