Calcification on CTCA of a CTO and PCI Outcomes

A chronic total occlusion (CTO) is present in 15-20% of patients who are referred for invasive coronary angiography. CTO Percutaneous Coronary Intervention (PCI) procedure success rates have increased over the years and can be as high as 90% when performed by high-volume CTO operators.Procedurally, excess calcification in the CTO anatomy is one factor which makes it difficult to complete the procedure or obtain ideal stent expansion. Excess calcification is best identified by Computed Tomography Coronary Angiography (CTCA) rather than invasive angiography.

The investigators plan to retrospectively evaluate CTCA in patients who underwent CTO PCI and correlate calcification characteristics with CTO PCI outcomes and tools utilised for calcium modification.

Cohort: All coronary CTO patients who underwent a PCI attempt and also underwent CTCA at our centre in the last 5 years.

Method of identifying and consenting patients: Screening of our local database to identify suitable patients who fulfil the inclusion/exclusion criteria. These patients will be telephoned and the consent form and participant information sheet will be maile dot them along with a self addressed stamped envelope.On receipt of the consent form, we will countersign it and return a copy to the patient. Consented patients' images and reports of the CTCA and CTO PCI will be reviewed.

Characteristics of calcification in the CTO on the CTCA will be evaluated including site, density and quantity of calcification. This will be correlated with CTO PCI outcomes of success and failure. Also this will be correlated with use of calcium modification tools for the CTO PCI.

* Baseline and demographic as well as procedural data will be compared with CTO PCI outcomes and presence/characteristics of calcification.
* Characteristics of calcification in the CTO assessed will include: site, density in Hounsfield units and quantity.
* Site of calcification (proximal, body or distal) will be correlated with the CTO PCI outcome by chi square analysis.
* Calcium density (in Hounsfield Units) on the CTCA will be correlated with successful versus failed CTO PCI by ROC curve analysis.
* Quantity of calcification will be assessed as a percentage of the cross section of the CTO body (as \<50%, 50-75% and 75-100%) and correlated with CTO PCI success by contingency analysis.
* Use of calcium modification tools will be correlated with CTO PCI outcome (success or failure) and density of calcification on CTCA (ROC curve and ANOVA).
* Categorical variables will be compared by the chi square or Fisher's test and continuous variables will be compared by the Mann Whitney U test. In addition, based on CTO PCI outcome of success or failure, patients will be compared for demographics and procedural variables.
* Categorical variables will be presented as percentage and compared with the chi square or Fisher's test
* Continuous variables will be presented as median (range) and compared with student's t-test or Mann Whitney test.

Eligibility Criteria:
Inclusion Criteria:

* Patients meeting all the below criteria will be included

  * ≥18 years
  * Previous CTO PCI attempt in the last 5 years
  * Undergone CTCA either pre or post CTO PCI
  * Adequate CTCA images for analysis

Exclusion Criteria:

* Patients meeting any of the following criteria will be excluded

  * \<18 years of age
  * Did not undergo CTCA
  * Inadequate/degraded CTCA images