Various CTO percutaneous coronary intervention (PCI) studies defined CTO as as a substantial atherosclerotic blockage with >3 months duration of TIMI (Thrombolysis in Myocardial Infarction) 0 flow other than via collaterals. Following CTO-PCI, various well-established therapeutic benefits have been extensively acknowledged, such as improved angina frequency score and quality of life score from the Seattle Angina Questionnaire (SAQ). Patients are currently referred for CTO PCI to relieve symptoms, reduce ischemia load, or pursue full revascularization to improve left ventricular ejection fraction (LVEF) CTO-PCI is one of the most difficult procedures in interventional cardiology today. Although IVUS has been demonstrated to improve long-term results during CTO PCI when used for stent optimization, its impact on crossing has received little research. IVUS imaging can aid in the resolution of proximal cap ambiguity by determining the position of the main branch and determining the position of the guidewire during CTO crossing efforts both antegrade and retrograde. For the reverse controlled antegrade and retrograde tracking and dissection (reverse CART) procedure, IVUS can help establish the best balloon size. In addition, imaging guidance can help in balloon and stent sizing, as well as stent expansion and strut apposition.

The function of IVUS in CTO PCI has been a source of contention among the four major CTO schools hybrid algorithms. The importance of IVUS-guided entry in overcoming proximal cap uncertainty was underlined in the Asia Pacific algorithm. Furthermore, IVUS-guided wiring, limited subintimal tracking and re-entry are incorporated in the algorithm as alternatives, but only as last resorts. After performing dual coronary injections, the North American hybrid method evaluates four angiographic characteristics, the first of which is a clear understanding of the proximal cap placement utilising angiography or IVUS. They also explain how IVUS guidance can help with reverse CART by allowing for the proper balloon size selection. When proximal cap ambiguity is found in the Euro CTO club algorithm, antegrade procedures such as IVUS-guided puncture and scratch and go technique are performed. When using a primary retrograde approach, the probability of antegrade passing with IVUS guidance and parallel wiring, as well as the advantage of a shorter guide wire crossing time when employing an antegrade route alone, must be incorporated in the Japanese algorithm.

Inclusion Criteria:

- All coronary CTO patients in whom coronary anatomy is defined by coronary CT and/or Coronary angiography provided that:- CTO defined as heavy atherosclerotic occlusion with TIMI (Thrombolysis in Myocardial Infarction) 0 flow other than via collaterals for >3 months and they are symptomatic despite optimal medical therapy and/or positive high risk stress modality.

Exclusion Criteria:

• Acute coronary syndrome within 3 months.
• Patients with renal insufficiency (eGFR < 60 ml/kg/m2, serum creatinine ≥ 2.5 mg/dL, or on regular dialysis).
• Patients with expected post CTO-PCI procedure SYNTAX >10.
• Hemodynamically unstable patients.