Do shock waves cause arrhythmias?

No. The delivery of shock waves is synchronized with the patient’s R-wave.  

During this period, the heart is in its refractory phase, thus, another action potential cannot be produced eliminating the risk for arrhythmia. The synchronization serves another purpose as well, as a means for precision in delivery of treatment as the heart will be at the exact state (End-Diastole) for every shockwave pulse.