heart rhythm and prolongation of the QT segment that controls the rate the heart beats.

Atypicals and many other drugs..including TCAs and valium, and SSRIs can prolong QT.

The best defense is understanding the risks and then you can still take the drugs with care.

1) genetic tendencies --this is usually hidden, and the best way to deal with it is to have a screening EKG to see what the QT time is. If delayed, then using drugs that prolong it further is
reconsidered.

2) developing low potassium and magnesium while taking QT risk drugs can bring on an event.
Examples are the drugs recently taken off the market, Seldane and Propulsid. Used in the wrong circumstances, or with other drugs that are additive, can lead to a cardiac QT event. You can develop low potassium and magnesium from the flu/dehydration.
From poor diet/intake, or from using other drugs that deplete them. (The drug Propulsid was taken off the market because many people were given diuretics by theirs doctors which depleted both electrolytes and were not monitored while using the Propulsid. This drug was commonly used along with acid blocking drugs to treat common GERD).

This website has grown considerably over the years. Please look at it. As new data comes in, drugs are added, or shifted around the 4 lists as needed.
http://www.azcert.org/

Basically it is up to doctors to screen you. And monitor you.
But they fail in this task. So it pays to understand the risks.
1) so you don't over-react and make yourself stressed out unnecessarily and
2) you don't get caught in a tragic situation.
You have to balance the two.

Not everyone gets a QT event. But when it happens it is terrible.

And also, there is evidence that a doctor who participated in the trials of Zyprexa, actually shredded the records of people who died under his care on that drug from cardiac events.

I post about this frequently... seems like I will be still doing that in the future!