X-AMINE ST: The X-Sizer in Acute Myocardial Infarction Patients for Negligible Embolization and Optimal ST Resolution
Presenter: Thierry Lefevre, MD, Institut Hospitalier Jacques Cartier (Massy, France)

Percutaneous coronary intervention (PCI) with stents is now considered the gold standard of treatment for patients with acute myocardial infarction (AMI). Although a significant number of AMI patients achieve restoration of normal coronary blood flow (TIMI 3), a large percentage still fail to achieve tissue-level reperfusion, as assessed by the myocardial blush score and by prompt ST-segment resolution.

Designed to restore reperfusion and improve visibility of the culprit vessel prior to PCI, the disposable, catheter-based X-Sizer (ev3 Inc, Plymouth, Minnesota) breaks up lesions using a spinning helical cutter and the resultant debris is then collected using the device's vacuum aspiration technology.

The X-Sizer in Acute Myocardial Infarction Patients for Negligible Embolization and Optimal ST Resolution (X-AMINE ST) study is a prospective, multicenter, randomized European trial that assessed the impact of thrombus extraction with the X-Sizer followed by standard PCI with stents in AMI patients who had thrombus and/or were at high risk for distal embolization. A total of 201 patients were randomized at 14 European sites to either PCI using the X-Sizer device (n = 100) or standard PCI (n = 101). The study protocol permitted the use of glycoprotein IIb/IIIa inhibitors and direct stenting, both of which were at the discretion of the operators.

Inclusion criteria included:

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  Acute MI < 12 hours
  
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  ST-segment elevation ≥ 2 mm in ≥ 2 contiguous leads
  
• 
  Killip class < 3
  
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  No thrombolytic therapy
  
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  Target vessel ≥ 2.5 mm
  
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  TIMI 0-1
  

Patients with right or left bundle branch block, as well as those with ostial or saphenous vein graft target lesions, were excluded from the study.

The study's primary endpoint was the mean magnitude of ST-segment resolution at 6 months. Secondary endpoints included:

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  ST-segment resolution > 50%
  
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  Slow flow, no reflow, or distal embolization
  
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  TIMI frame count
  
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  Myocardial blush score
  
• 
  Regional wall motion index
  
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  Major adverse cardiac events (MACE) rate at 1 and 6 months
  
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  Procedural costs
  

Results
Baseline clinical and procedural characteristics were similar between the 2 groups; however, significantly more patients pretreated with the X-Sizer device underwent direct stenting (Table).
Table. Baseline and Procedural Characteristics

Characteristics	No X-Sizer (n = 101)	X-Sizer (n = 100)
Age (yrs)	62 ± 11	60 ± 14
Female (%)	27	24
Diabetes (%)	18	25
Hypertension (%)	50	53
Hyperlipidemia (%)	61	57
Smoker (%)	51	51
Prior MI (%)	6	10
Anterior wall MI (%)	56	52
Onset of pain to angiograms (min)	263 ± 195	251 ± 149
Procedural Characteristics
GP IIb/IIIa inhibitors (%)	58	54
Stent placement (%)	99	100
Direct stenting (%)*	34	58

*P < .01
GP, glycoprotein; MI, myocardial infarction

The procedure was successful in 89% of patients treated with the X-Sizer, and thrombus was removed in 95% of these cases; complete thrombus removal was seen in 39% and partial thrombus removal in 61% of patients. Baseline and final quantitative measurements of the coronary arteries were similar between the 2 groups. There was no significant difference between the control group and X-Sizer-treated patients with regard to the rate of final TIMI 3 flow achieved (89% vs 95.7%; P = NS).

There was a significantly lower incidence of slow flow or no reflow in patients assigned to X-Sizer, with a significant reduction in distal embolization at the expense of a prolonged procedural time (10 additional minutes) (Figure 1).


Figure 1. X-AMINE ST: slow flow and distal embolization.
For those with available electrocardiogram data pre- and postprocedure (n = 185), the primary endpoint, ST-segment resolution > 50%, was achieved significantly more often in X-Sizer-treated patients than in controls (67.4% vs 53%, respectively; P = .052) (Figure 2). There were no significant differences in the rate of death, reinfarction, reintervention, or MACE at 1-month follow-up (Figure 3).


Figure 2. X-AMINE ST: primary endpoint - ST segment resolution.

Figure 3. X-AMINE ST: clinical outcomes at 30-day follow-up. Conclusions
On the basis of the 30-day and 6-month follow-up data, investigators concluded that the use of the X-Sizer catheter system in AMI patients undergoing primary PCI resulted in a higher incidence of ST-segment resolution, with lower rates of distal embolization, slow flow, or no reflow phenomena.
Comments
The X-Sizer is a user-friendly device that may help reduce the thrombus burden during coronary intervention in AMI patients. The results of the present study showed that it is feasible and safe to use this device, and a substantial reduction in distal embolization and slow flow or no reflow can be achieved. Furthermore, use of the device only increased procedural time by an average of 10 minutes. Obviously the sample size is too small to be able to observe a significant difference in hard endpoints, such as death.

Nevertheless, a higher percentage achieved > 50% ST-segment resolution, an important predictor of long-term outcome. Larger studies and the publication of all the parameters measured during the study will give us a greater understanding of the possible benefits of this device.