The value of intravascular ultrasound in patients with acute myocardial infarction

Choosing the best percutaneous coronary intervention (PCI) strategy in patients with acute myocardial infarction based only on angiographic characteristics is difficult, since the mechanism can differ between cases (spontaneous plaque rupture or erosion and subsequent thrombosis) [1]. There are invasive modalities to determine the best strategy, and these include intravascular ultrasound (IVUS) and optical coherence tomography (OCT), methods that could underline plaque rupture, thrombus, positive remodeling, greater plaque burden, and tissue prolapse. Virtual histology, done by IVUS, is capable of detecting lesions containing large necrotic cores and thin cap fibroatheroma (independent predictors of no-reflow in acute myocardial infarction). IVUS has a crucial role in depicting plaque characteristics, periprocedural complications, and plaque evolution. These imagistic modalities can lead the PCI strategy in order to obtain the best possible outcome of the procedure for the patient.

We report the case of a 58-year-old male patient admitted to our clinic with ST-segment elevation myocardial infarction (STEMI) at 4 hours after pain onset, that had received thrombolytic therapy with reteplase 10U bolus followed by another 10U bolus after 30 minutes at 2 hours after pain onset without reperfusion criteria. The past medical history of the patient was unremarkable. His cardiovascular risk factors were stage I hypertension, dyslipidemia, smoking, and male sex.

Clinical examination at the emergency room revealed a normal blood pressure without any therapy and no other abnormal clinical signs. The electrocardiogram revealed a third-degree atrio-ventricular (AV) block with negative T waves in the inferior leads and ST segment elevation in posterior leads. Transthoracic echocardiography showed a mild reduced left ventricular ejection fraction of 45%, hypokinesis of the inferior wall, and mild to moderate mitral regurgitation.

Because we were dealing with a posterior STEMI in the first 4 hours from pain onset, we proceeded to invasive evaluation. Coronary angiogram showed a left coronary artery without any notable lesions (figure 1 and 2), but we found a massive thrombus in the right coronary artery that extended from the second segment of RCA to the distal part of both posterolateral artery (PLA) and posterior descending artery (PDA) (figure 3). Because of a high thrombus burden, we decided to perform aspiration thrombectomy. Since both PDA and PLA were important vessels, we engaged the RCA with a 7.0 French Judkins Right guiding catheter. We used a 7.0 French guiding catheter to be able to pass simultaneously two guidewires and an aspiration thrombectomy catheter.

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Since the thrombus extended into both PLA and PDA, we made multiple passages to both vessels, obtaining a TIMI III flow with a small amount of residual thrombus (figure 4,5).

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Because after the aspiration thrombectomy we hadn’t revealed any important stenosis in the RCA, we decided to perform IVUS to assess the lumen of the vessel, searching for the culprit lesion. IVUS depicted important plaque burden in the second segment of the RCA, an ulcerated plaque, best assessed by ChromaFlo recording without dissection or significant stenosis (figure 6,7,8,9). Minimal lumen area was more than 4 mm² along the entire RCA [2]. Some residual, mobile thrombus was still present in mid RCA, which we decided to treat with intravenous anticoagulants.

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The recovery of the patient was good and the AV block was resolved. He was discharged without symptoms and with an improved left ventricular ejection fraction.

In a patient with right dominant system, RCA is a rather big artery that is supplying more than just the right ventricle and right atrium, since the posterior descending artery emerges from it. As a consequence, we’ve seen the transitory third-degree AV block resolved after obtaining an optimal blood flow in the RCA. Thrombectomy catheters, while unwieldly, aids thrombus aspiration. Manual aspiration thrombectomy has been studied in large randomized controlled trials and arisen as the preferred method of thrombectomy due to its ease of use. Infarct size was found to be less in patients undergoing thrombectomy before stenting compared with controls undergoing stenting without prior thrombectomy [3]. However, this strategy can also be used as bail-out in presence of a high thrombus burden, or if TIMI flow of less than 3 persists despite balloon angioplasty before stenting [4].

The above case highlights the importance of aspiration thrombectomy as possibly the best option in selected cases. Also, IVUS proved that it should be used more often in selected cases, since it could change the whole approach of the PCI [5,6]. Based on IVUS finding, we can defer stenting of insignificant coronary lesion that can be difficult to assess only by angiographic images.

After carefully analyzing the images obtained from IVUS, we decided not to stent the lesions since we hadn’t found any residual stenosis that could jeopardize the patient in the future and implanting a stent would not have a significant advantage in this case. We opted instead for optimal pharmacological treatment and reassessment after 3 months, in order to achieve the best outcome, having in mind that IVUS guided PCI was associated with lower rates of all-cause mortality (RR 0.7; 95% CI, 0.59–0.82; p < 0.01), major adverse cardiovascular events (RR 0.86; 95% CI, 0.74–0.99; p = 0.04), and target vessel revascularization (RR 0.83; 95% CI, 0.73–0.95; p < 0.01) at a median follow up of one year [7] (figure 10).

Figure 10

Coronary angiogram offers limited information for planning the PCI strategy based on anatomical characteristics only, typically in patients with multiple coronary lesions and thrombotic lesions. The most important goal of PCI in a patient with STEMI is to restore the blood flow to relieve the myocardial ischemia as fast as possible. Placing a stent on all coronary lesions seen on coronary angiogram without certifying the impact of these lesions can complicate the procedure and jeopardize the outcome of the patient. There are a lot of data showing that PCI guidance by invasive imagistic and physiological investigation methods improves the outcome of the patient, with clear cut-offs for assessments that can guide us to achieve the best result with an adequate percentage of MACEs at the mid-term follow-up [8].