Acute MI Intervention
Distal protection improves the outcome of coronary intervention.
To view the tables that correspond to this article, please refer to the print version of our November/December issue, page 24.
Percutaneous intervention during an acute MI is one of the most gratifying procedures that a cardiologist can perform. This approach requires a skilled team including an interventionalist, a nurse, a technologist, and often a fellow. Opening an occluded artery with immediate resolution of pain and ST segment abnormality, and frequently improved hemodynamics provides a sense of accomplishment to the physician and immense gratitude on behalf of the patient.
Since Geoffrey Hartzler, MD, and William O’Neill, MD, first promoted this form of therapy in the early days of balloon angioplasty (1984-1986), we have made excellent progress in refining the technique and as a result, we now achieve better outcomes.1,2 Distal protection is the latest step in improving this procedure.
Thrombolytic trials have produced a scoring system for coronary flow that has now become antiquated and no longer truly describes the desired end point of reperfusion therapy. More sophisticated methods of measuring reperfusion now exist. These newer scoring techniques more accurately reflect the success of reperfusion. Available methods of evaluation include:
• ST segment resolution
• Myocardial blush score
• Basal and peak coronary blood flow velocity
• Contrast echo
• Enhanced MRI
• PET and thallium
ST Segment Resolution
There is indirect evidence supporting the use of ST segment resolution as a measure of reperfusion. Van ’t Hof demonstrated in more than 400 acute infarct patients that complete ST segment resolution resulted in a statistically improved predischarge ejection fraction.3 These results also translated into a reduced 1-year mortality rate. Table 1 shows the ejection fraction and 1-year mortality rates correlating with complete and partial ST segment resolution, as well as for persistent ST segment elevation.
Myocardial Blush Scoring
Stone et al examined blush scores and reperfusion outcomes.4 In 173 acute infarct patients treated with mechanical reperfusion, a grade 1 or grade 0 blush score correlated with a 1-year mortality rate of 22%. A grade 2 score was associated with a 13% mortality rate, and a blush score of grade 3 had the lowest risk of death at 6.8%.
It is clear from the published data that outcomes from mechanical reperfusion of acute MI are highly dependent upon obtaining excellent reperfusion with as little downstream debris as possible. Distal small vessel plugging by debris from the culprit lesion appears to be responsible for inadequate ST segment resolution and lower blush scores. A large multicenter randomized trial (the EMERALD trial) is currently underway to test the hypothesis that distal protection in acute MI produces better reperfusion.
The PercuSurge GuardWire Plus Temporary Occlusion and Aspiration system (Medtronic AVE, Inc., Santa Rosa, CA) captures embolic debris that might otherwise block downstream vessels. It consists of a balloon-tipped guidewire, which is inflated briefly to occlude blood flow and halt any debris dislodged during stent placement. The interventionalist then withdraws captured material by using the PercuSurge Export aspiration catheter (Medtronic AVE, Inc.), the balloon is deflated, and blood flow restored. This distal protection device has been successfully tested in saphenous vein grafts and was approved by the FDA for this indication. Preliminary testing strongly suggests that this device will be efficacious in the mechanical treatment of acute MI patients. In preliminary testing of the device, Stone et al demonstrated the PercuSurge GuardWire’s effectiveness in an acute MI setting compared with previously published data (unpublished data, 2002). There was a marked difference in blush score in patients who were treated with distal protection during acute MI intervention (Table 2).
At North Shore University Hospital, in Manhasset, New York, my colleagues and I have a long history of treating acute MI by mechanical means. Annually, we treat just fewer than 400 acute MI patients within the 12-hour window. Almost half of these cases are transferred from neighboring hospitals because of failed thrombolytics, or because of contraindications to thrombolytics. We have started to receive a growing number of acute MI patients transferred for immediate coronary intervention without thrombolytic therapy, although there is no contraindication. In these cases, the referring cardiologists believe that immediate transfer for coronary intervention is superior to first trying thrombolytics, and then transferring.
We recently examined our patient population and demonstrated that “rescue” patients (acute MI patients who had failed thrombolytic therapy) had a higher intracoronary thrombus score than those treated on site without prior thrombolytics.5 Although there was no difference between these two groups in final TIMI flow grade at the end of the procedure, there was a statistically higher corrected TIMI frame count (CTFC) in the rescue group, implying less-effective coronary reperfusion in these patients. Table 3 provides a comparison of the scores in these two groups.
One explanation for the improved coronary reperfusion in the nonthrombolytic group was thought to be the higher use of Abciximab (Eli Lilly, Indianapolis, IN) (30% in the nonthrombolytic group vs 2% in the rescue group), but regression analysis revealed thrombus score and initial CTFC to be independent predictors of final CTFC (P=.028 and P=.001, respectively). We therefore concluded that failed thrombolysis followed by primary stenting was an ideal setup to benefit from distal protection (Table 4). Thus, it has become a more common practice in our facility to use distal protection when treating acute MI patients with stenting. We subsequently reviewed 231 recent acute MI patients and compared CTFC in three different groups (Park C, Salem M, Jauhar R, et al, unpublished data, submitted 2002). The group of acute MI patients who were protected by the GuardWire device during stenting showed the lowest frame counts.
PRESERVE VENTRICULAR FUNCTION
The use of primary coronary intervention for the treatment of acute MI is becoming more popular, not only as a primary treatment but also as a rescue procedure for patients who fail thrombolytics. Coronary intervention procedures for MI are taking place at nonsurgical sites; the skilled teams performing these procedures are achieving outcomes similar to those at larger, full-service sites.
Long-term survival is related to the amount of preserved left ventricular function, which is the main reason for performing these procedures. Many interventionalists hypothesize that if reperfusion is accomplished with minimal or no distal emboli of lesion debris, then more myocardial function will be preserved with better long-term outcomes. Distal protection is the first step in this direction and will evolve over the next few years as newer and easier-to-use devices (filters) become available. As interventionalists combine the expert use of drug-eluting stents with improved distal protection, it seems realistic to expect that acute MI outcomes should continue to improve.
Stanley Katz, MD, is Chief of Cardiology at North Shore University Hospital in Manhasset, New York. Dr. Katz may be reached at (516) 562-4101; email@example.com.
1. Hartzler GO, Rutherford BD, McConahay DR. Percutaneous transluminal coronary angioplasty: Application for acute myocardial infarction. Am J Cardiol.1984;53:17c-21c.
2. O’Neill W, Timmis GC, Bourdillon PD, et al. A prospective randomized clinical trial of intracoronary streptokinase versus coronary angioplasty for acute myocardial infarction. N Engl J Med. 1986;314:812-818.
3. Van ’t Hof AW, Liem A, DeBoer MJ, Zijlstra F. Clinical value of 12-lead electrocardiogram after successful reperfusion therapy for acute myocardial infarction. Lancet. 1997;350:615-619.
4. Stone GW, Peterson MA, Lansky AJ, et al. Impact of normalized myocardial perfusion after successful angioplasty in acute myocardial infarction. J Am Coll Cardiol. 2002;39(4):591-597.
5. Salem M, Freeman J, Katz S, et al. Intracoronary thrombus score and corrected TIMI frame count in rescue stenting compared with primary stenting in acute myocardial infarction [abstract]. Am J Cardiol. 2002;90(suppl 6a):190H.