Normal sinus rhythm
Irregular rate, but good QRS complex
Use "Arrythmia Detection" and set the value to 300-400.
This will reject data from a heartbeat in which the next R wave came earlier or later than a 300-400 msec window centered on the expected R wave.
Breathhold time will increase.
If images still have cardiac motion artifact (be sure to differentiate from respiratory motion artifact), use Prospective Triggering and Capture Cycle
Irregular rate, no identifiable QRS complex
Neither retrospective or prospective triggering will work if the scanner cannot identify QRS complexes accurately.
First step - adjust ECG leads, and relearn VCG
Second step - reboot system
If this doesn't work, the exact can only be performed with real-time acquisitions and may not be diagnostic depending on the clinical indication