possible heart problems during ecg triggered lithotripsy

Hi
I have the following question: If a patient has a heart problem, but still needs lithotripsy treatment for kidney stones, on which part of the ecg-curve should the lithotripter be triggered, so as not to induce a disrhytmic behaviour in the heart or even worse?
I hope somebody can give me an answer to this.
Thank you very much in advance.
Best regards
Bettina

[Cleveland Clinic, MD]

Dear Bettina,

The period of vulnerability to arrhythmias is during repolarization of the ventricles.  This is the T wave on the ECG.  The period of safety is during depolarization which correlates to the QRS complex on the ECG.  Therefore the part of the ECG to trigger off of is the QRS complex.

[bettina]

Hi
Thank you very much for your fast reply.
After studying your answer, I have now learned, that the QRS complex has a the so called R-peak. Now my next question would be: If the trigger is within this QRS complex (which seems to be quite long) would it create any hazard to the patient if the shock wave hits the patient on either the up- or down-coming slope of this R peak?
Thanks again for your help.
Best regards,
Bettina