No.

Please don't use the USB connector for ECG leads, because that's unsafe.
Let's do a spot of risk analysis. Imagine the ECG electrodes connected to a patient on one end, and to a USB jack on the other end. Imagine all the places where somebody could accidentally stick the USB jack into: laptops, smartphones, counterfeit Chinese wall chargers.
What kind of benefit can outweigh such risk?

More generally. Exposing common connectors (HDMI, USB, RJ-45, etc) for other purposes is usually a wrong idea.

No.

Please don't use the USB connector for ECG leads, because that's unsafe.
Let's do a spot of risk analysis. Imagine the ECG electrodes connected to a patient on one end, and to a USB plug on the other end. Imagine all the places where somebody could accidentally stick the USB plug into: laptops, smartphones, counterfeit Chinese wall chargers.
What kind of benefit can outweigh such risk?

More generally. Exposing common connectors (HDMI, USB, RJ-45, etc) for other purposes is usually a wrong idea. But [the opposite] using an uncommon or proprietary connector for common communication interfaces is fine.