Percutaneous coronary interventions (PCI) is intended to relieve myocardial ischemia by improving blood flow in the epicardial coronary arteries. However, the efficacy of PCI may be compromised by incidental microvascular obstruction and peri-procedural myocardial infarction (PPMI), which occurs in about 10-15% of cases and is associated with increased rates of major adverse cardiovascular events (MACE). The mechanism of PPMI is thought to be related to side branch occlusion, coronary artery dissection and acute microvascular damage caused by embolization of plaque debris during the PCI and is more frequently seen in calcified coronary artery disease. Calcium modification by rotational atherectomy (RA) results in peri-procedural myocardial infarction in 24% of cases and myocardial injury in 70% of cases. The Shockwave coronary intravascular lithotripsy (IVL) balloon catheter emits sonic pressure waves in a circumferential field causing the selective fracture of calcium, altering vessel compliance and permitting further expansion of the vessel wall. This provides a potentially safer alternative to other calcium-modifying devices since there is a low risk of dissection and perforation. It is also proposed that this IVL device reduces the risk of atheromatous embolization, which would reduce the risk of PPMI and microvascular dysfunction. The SONAR Trial is a pilot study measuring peri-procedural myocardial injury, PPMI and microvascular dysfunction in patients (with calcified coronary artery lesions not responding to usual balloon dilatation) randomized to RA or Shockwave IVL. The primary outcome is peri-procedural myocardial infarction. Secondary outcomes include peri-procedural myocardial injury, acute microvascular dysfunction, procedural success, and procedural costs.