Why mornings are deadliest for heart attack deaths

An Indian scientist has claimed that evidence from people suffering from heart disease supports the existence of the molecular link first discovered in laboratory mice between the body's natural circadian rhythms and cardiac arrest or sudden cardiac death.

Mukesh Jain, M.D., said that it pinpoints a previously unrecognized factor in the electrical storm that makes the heart's main pumping chambers suddenly begin to beat erratically in a way that stops the flow of blood to the brain and body.

Termed ventricular fibrillation, the condition causes sudden cardiac death (SCD), in which the victim instantly becomes unconscious and dies unless CPR or a defibrillator is available to shock the heart back into its steady beat.

The peak risk hours when SCD strikes range from 6 a.m. to 10 a.m., with a smaller peak in the late afternoon. Scientists long suspected a link between SCD and the 24-hour body clock, located in the brain.

It governs 24-hour cycles of sleep and wakefulness called circadian rhythms that coordinate a range of body functions with the outside environment.

Jain's group discovered a protein called KLF15 that helps regulate the heart's electrical activity, and occurs in the body in levels that change like clockwork throughout the day. KLF15 helps form channels that allow substances to enter and exit heart cells in ways critical to maintaining a normal, steady heartbeat.

They first discovered that patients with heart failure have lower levels of KLF15. Then, they established in laboratory mice that KLF15 is the molecular link between SCD and the circadian rhythm. And mice with low levels of the protein have the same heart problems as people with SCD.