More than one million percutaneous coronary interventions are carried out each year in the US, 70% resulting in the placement of a coronary stent.1 As more stents are placed, greater need arises for post-procedure evaluation of stent patency and progression of native coronary disease in patients with recurrent symptoms. This follow-up becomes even more imperative when it is considered that in-stent restenosis occurs in nearly 7% of patients, even in the age of drug-eluting devices. The incidence of restenosis is even higher in cases of ostial stenting, stent overlap, and diabetes.1 Follow-up exercise stress testing with radionuclide imaging is not recommended in asymptomatic patients within two years of an intervention.2 Limited experience exists in using coronary computed tomographic angiography (CTA) to assess coronary stent patency. The authors present a case using cardiac CTA for the evaluation of a coronary stent in a clinical scenario that has not yet been addressed by appropriate, formal coronary CTA utilization criteria.
A 77-year-old female with a history of hypertension and hyperlipidemia presented with exertional angina and shortness of breath. She underwent exercise stress testing with nuclear imaging, reproducing her symptoms but failing to demonstrate electrocardiographic abnormalities or single photon emission computed tomography myocardial perfusion defects. Left ventricular function was normal at rest, with no segmental wall-motion abnormalities and an ejection fraction of 60%. Due to continued symptoms highly suggestive of myocardial ischemia, the stress test was thought to be a false-negative.
The patient underwent coronary angiography, which revealed multiple non-critical lesions throughout the left coronary artery system. The left main coronary artery had a distal 20% lesion. The left anterior descending artery was normal, but the first diagonal branch had a 40–50% stenosis. A 30–40% proximal stenosis was noted in the left circumflex artery. Angiography of the right coronary artery (RCA) revealed complex 99% ostial and proximal stenosis associated with marked calcified plaque, see Figures 1A and 1B. Percutaneous coronary intervention was performed on the right coronary lesion. Guide catheter seating at the right coronary ostium was difficult. Rotablation was performed due to the calcified plaque (two passes with a 1.5burr for 20 seconds at 170,000rpm). The lesion was then dilated with a 2.5x6mm cutting balloon, see Figure 1C. A 4x23mm drug-eluting stent was then deployed, with residual stenosis probably due to incomplete expansion of the calcified plaque, see Figure 1D.
Post-stent dilatation was therefore performed with a 4.5x8mm high-pressure balloon, producing an improved but still suboptimal angiographic result, see Figure 1E. The patient was followed periodically by her cardiologist. She denied any chest pain or shortness of breath, but was relatively inactive. She was compliant with all her medications. Given her sedentary lifestyle, the ostial location of the lesion, the fact that previous non-invasive diagnostic testing failed to reveal a defect and the sub-optimal stent deployment due to calcified plaque, a decision was made to reassess the RCA anatomically. Coronary CTA was chosen rather than intra arterial coronary angiography, in light of the technical difficulties previously encountered engaging the RCA and the risk of damaging the ostial stent.
Coronary Computed Tomographic Angiography
Multidector computed tomography of the heart and coronary arteries was performed using a 64-channel scanner. The patient received 150mg of oral metoprolol two hours prior to study. Sublingual nitroglycerin 0.4mg was administered 10 minutes prior to study. Scanning was performed with 120kV with milliamp-sec 700 with radiation dose modulation using 0, 40, 70, 75, and 80% phases with slice thickness of 0.8mm. Angiography was performed with 100ml iopadmidol injected at 6ml/second followed by 50ml of saline at 6ml/second. Post processing was performed with a stent filter. Coronary CTA showed dense focal calcified plaque at the ostial and proximal segments of the RCA. The stent was patent without any significant in-stent stenosis, although there were discrete areas where the calcified plaque impaired complete expansion of the stent. There was good contrast filling of the RCA beyond the stent with Hounsfield units nearly equal to that of the aortic root, implying adequate flow through the stent (see Figures 2A–C).
The 2010 Appropriateness Criteria for Cardiac Computed Tomography generally consider the use of coronary CTA in the asymptomatic post-percutaneous coronary intervention patient population as inappropriate, except in left main coronary artery stenting. In cases of symptomatic patients, coronary CTA is considered inappropriate when stent diameter is <3mm and of uncertain benefit when stent diameter is >3mm.3,4 This case demonstrates an interesting, yet not uncommon, circumstance in which the clinical scenario is not specifically addressed by established guidelines and appropriate use criteria. Ostial stenting of a dominant right coronary system may be yet another circumstance where coronary CTA should be considered. The promise of coronary CTA to provide accurate anatomic visualization of the coronary arteries and intra-coronary stents may be considered in patients at high risk for post-percutaneous coronary intervention in stent stenosis. This will avoid the need to subject patients to the morbidity and mortality of invasive procedures. Furthermore, the future development of cardiac CTA technology and stent design may facilitate non-invasive imaging for follow up.