Clinical Outcomes and Prevalence of Intravascular Ultrasound Use at a Tertiary Care Hospital in a South Asian Country

INTRODUCTION

Intravascular ultrasound (IVUS) is an invasive imaging modality used to visualize coronary cross-sectional anatomy.^[1] IVUS technology has been proven to be superior to coronary angiography in terms of the assessment of vessel size, plaque composition, vessel dissection, calcium content, and lesion severity. However, despite these benefits, routine IVUS use is limited by cost and additional time that is needed to perform the procedure.^[2]

Percutaneous coronary intervention (PCI) of the left main (LM) vessel and complex lesions remains challenging with a higher risk of procedural complications and poor early and late outcomes. The role of IVUS guidance has been previously explored, however, limited information is available on how the pre-procedural use of IVUS might impact the intervention strategy and clinical outcome, particularly when approaching complex coronary lesions. We believe that additional information provided by IVUS beyond angiography leads to more optimal results and improving the outcome after PCI, particularly in the LM intervention.^[3] Given the continuous expansion of PCI for treating sicker patients and more complex coronary lesions, we believe that IVUS plays a pivotal role in the current practice era of complex PCI.^[4] In this study, we described the prevalence and clinical outcomes in current practice at a tertiary care hospital in a low- to middle-income South Asian country, Pakistan.

MATERIAL AND METHODS

This is a single-center, retrospective observational study.

RESULTS

A total of 134 patients who underwent IVUS imaging between January 2013 and March 2020 and fulfilled the inclusion criteria were included in our study. Baseline characteristics are shown in Table 1. The majority of the patients included in our study were male (72.3%) and the mean age at presentation was 63.1 ± 12.9 years. The prevalence of utilization of IVUS at our center was 3% and the majority of IVUS was done in 2020 [Figure 1]. The most common comorbidity noted was dyslipidemia (n = 111 [82.8%]) followed by hypertension (n = 104 [77.6%]). Notably, non-ST-elevation MI (n = 50 [37.3%]) was observed to be the main reason for presentation. The most common medication prescribed at discharge was statins (n = 128 [99.2%]) followed by dual antiplatelet (n = 125 [97.9%]).

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Figure 1:

A 56-year-old lady came to emergency with chest pain and recurrent polymorphic ventricular tachycardia. Intravascular imaging of the left anterior descending artery done showing mean luminal area and mean luminal diameter.

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The procedural characteristics are shown in Table 2. The most common route of access adopted for the procedure in our study population was femoral access (n = 69 [51.5%]). Although the LM disease was found (n = 46 [34.3%]), single-vessel disease was most commonly noted (n = 51 [38.1%]). Drug-eluting stents (n = 92 [68.6%]) were deployed in the majority of patients.

The IVUS details are shown in Table 3. The IVUS was done mostly in the left anterior descending artery (n = 94 [70.1%]) followed by the LM (n = 46 [34.3%]). The LM mean MLA was 6.0 ± 2.6 mm² and the mean MLD was 4.53 ± 0.6 mm. Coronary artery dissection was noted in 11.2% of patients (n = 15).

In our study, we were able to collect follow-ups of all patients [Table 4]. The mean duration of follow-up in our study was 40.3 ± 30.1 months. MACE occurred in n = 13 (9.7%) patients, which was largely driven by heart failure (n = 4 [3%]). Cardiovascular death and TVR occurred in n = 3 (2.2%) patients.

The procedural characteristics are shown in Table 2. The most common route of access adopted for the procedure was femoral access, n = 69 (51.5%), in our study population. The LM disease was found in n = 46 (34.3%), however, the single-vessel disease is n = 51 (38.1%) most commonly noted. The drug-eluting stents, n = 92 (68.6%), were deployed in the majority of patients.

The IVUS details are shown in Table 3. The IVUS was done mostly in the left anterior descending, n = 94 (70.1%) followed by LM, n = 46 (34.3%). The LM mean MLA was 6.0 ± 2.6 mm² and the mean luminal diameter was 4.53 mm ± 0.6 [Figure1]. In our study, we found coronary artery dissection in 11% (n = 15) of total cases, which were either iatrogenic (before the use of IVUS in index procedure) or primary spontaneous dissection. Calcification and stent underexpansion were noted in 57.5% (n = 77) [Figure 2] and 34.3% (n = 46) [Figure 3], respectively. Dual antiplatelets aspirin (75–150 mg) and clopidogrel (75 mg) were prescribed to most of the patients who underwent revascularization at the time of discharge for 1 year and then switched to single antiplatelet.

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Figure 2:

A 66-year-old gentleman came with complaint of unstable angina. Intravascular imaging of the left anterior descending artery done showing significant calcification (arrow).

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Figure 3:

A 68-year-old gentleman came with complaint of stable angina. The patient had previous stenting in LAD 6 months back. Intravascular imaging of the left anterior descending artery done showing significant underexpansion of stent (Stent: Solid arrow, vessel wall: Hollow arrow).

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In our study, we were able to collect follow-up of all patients [Table 4]. The mean duration of follow-up in our study was 40.3 ± 30.1 months. MACE occurred in n = 13 (9.7%), which was largely driven by heart failure n = 4 (3%). Cardiovascular death and TVR occurred in n = 3 (2.2%).

DISCUSSION

The results of the present study help us to acknowledge the prevalence and outcomes of IVUS guided PCI in our population. This is the first study from Pakistan on IVUS with such an extended period of follow-up. Our analysis demonstrated that the use of this ancillary modality improves clinical outcomes of PCI in terms of MACE. Similar improvement in MACE has been noted in the previous studies from upper and upper-middle-income countries.^[5-12]

The utilization rate of IVUS in our hospital is 3.0% which in comparison to upper and upper-middle-income countries is significantly low [Figure 4]. The use of IVUS varies in different parts of the world. Data from the USA demonstrated IVUS use in 5.6–20% of cases,^[13-15] Japanese multicenter PCI registry data show IVUS use in 84% of cases,^[16] in Italy, IVUS was used in 5.2% of cases in bifurcations lesions,^[17] and a large center Korean registry showed IVUS use in 27.9% of cases of complex PCI.^[18] The previously published data from Japan demonstrated frequent use of IVUS in the last decade and that’s might be the reason for reduced mortality, stent thrombosis, and in-stent restenosis (ISR) as compared to many European countries.^[15] The major reason behind low utilization of IVUS was increased cost of the procedure, additional time needed for the procedure, and lack of confidence in intravascular imaging (IVI). However, we observed an upgoing trend of utilization of IVUS in the last several years at our center. But still, the use of IVUS technology needs a significant increase to improve both short- and long-term outcomes by decreasing incidences of iatrogenic coronary dissection, stent thrombosis, and ISR. In our study, iatrogenic coronary dissection with IVUS use was zero. Iatrogenic coronary dissection rates of 4.26% were reported by Khalid et al. in the IVUS arm while^[7] the SIPS trial reported 3% rate of iatrogenic coronary dissection due to IVUS, with exclusion of chronic total occlusion (CTO) lesions and emergent procedures.^[19] A possible explanation for this difference could be relatively smaller sample size in our study.

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Figure 4:

Prevalence of IVUS use over years 2013–2020. IVUS: Intravascular ultrasound.

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In our study, post-PCI IVUS evaluating stent expansion revealed suboptimal expansion in n = 46 (34%) of cases thus requiring further post-dilation. It was also observed in our study that IVUS was more frequently used post PCI for the assessment of adequate stent expansion and ruling out edge dissections in suspected cases. The higher incidence of stent underexpansion can also be explained by selection bias, with IVUS being primarily done in cases where non-optimal post-PCI results such as under expansion were suspected.

Our follow-up period in comparison to other studies was longer.^[8,19] In the present data, total events rates on follow-up were 13% which is comparable to what Schroeder et al.,^[18] observed, 14%, and were 12% in SIP trial.^[19] In our study, target vessel/lesion failure was only 2.24% (n = 3), which is incredibly very low in comparison to Intracoronary Stenting and Antithrombotic Regimen trial,^[20] 14.6%, SIPS trial TLR was 17%, Jeremias et al. have also used IVUS guidance for stent placement and found 33.3% restenosis rate at 6 months.^[21] However, we need a multicenter randomized trials and further large sample size studies in this regard. The findings of our study will help to increase the confidence in utilization of IVUS and would improve clinical outcomes.

Two predominant IVI modalities are IVUS and optical coherence tomography (OCT). The basic principle of IVUS imaging is the oscillatory movement of a piezoelectric transducer (crystal), resulting in generation of sound waves when electrically excited.^[1] The sound waves generated by transducers propagate through and reflect off different tissues, varying according to acoustic properties of the tissues. OCT generates images by measuring the echo time delay and intensity of light that are reflected/backscattered from the tissues. OCT has high resolution and low penetration while IVUS has lower resolution but high penetrance as compared in Table 5.^[22-26] Due to scattering of light from erythrocytes, OCT requires temporary clearance of the vessel lumen using contrast injection to improve image quality.^[24]

Our study has several limitations; it’s a retrospective, single-center study, coronary angiography and revascularization were clinically driven, so were performed only in those patients who were symptomatic after the index procedure. IVUS use during PCI was dependent on the operator’s decision either for pre-PCI assessment of lesion or post-PCI, for evaluation of stent expansion or suspicion of dissection. Detailed IVUS parameters such as plaque burden, plaque contents quantification, calcium quantification, or post-PCI measurements were not recorded.

CONCLUSION

IVUS technology is an adjunctive tool to coronary angiography in lesions requiring detailed assessment, stent deployment, evaluating stent expansion, and dissection which results in a significant decrease in MACE, both in hospital and on follow-up and hence cost effective. Our data might support the broader use of IVUS in both developed and in our part of the world.