LETTER TO THE EDITOR
Prognostic significance of coronary blood flow velocity patterns in patients with reperfused acute myocardial infarction and TIMI-2 flow
Philippe Garot, MD
Federation de Cardiologie, Hôpital Henri Mondor, AP-HP, 51, avenue Maréchal de Lattre de Tassigny, 94010, Creteil, France
philippe.garot{at}hmn.ap-hop-paris.fr
Yamamoto et al. (1) in a recent issue of the Journal reported that the Thrombolysis In Myocardial Infarction trial (TIMI-2) flow after primary angioplasty for acute myocardial infarction (AMI) may be related to either thrombus burden in the infarct-related artery or microvascular injury, and then be associated with systolic flow reversal (SFR) on coronary blood flow velocity (CBFV) patterns. The investigators concluded that: 1) two different CBFV patterns including or not including the presence of SFR exist in patients with reperfused AMI and TIMI-2 flow; 2) patients with SFR have increased microvascular damage and consequently worse functional and clinical outcome; and 3) patients without SFR have slow forward flow in the epicardial coronary artery associated with a higher systolic/diastolic velocity, suggesting an increase in arterial resistance due to presence of thrombus burden.
The presence of SFR on CBFV measured immediately after prompt reopening of the culprit coronary artery has been associated with poor functional recovery (2,3) and worse clinical outcome (4). However, the researchers have not taken into account the confounding and fundamental role played by infarct size in compromising both functional and clinical outcome. As opposed to patients without SFR, it appears that patients with SFR had much larger infarcts with much more frequent rates of anterior location. In contrast, patients without SFR had normal systolic function and therefore limited inferior infarcts. Consequently, and contrary to previous reports, the patients did not exhibit functional improvement at follow-up. Because primary angioplasty was performed within a similar range of time elapsed from pain onset in patients with and without SFR, it is noticeable that the difference in systolic function and left ventricular remodeling was related to a difference in area at risk and infarct location between the two groups of patients. Because the investigators used myocardial contrast echocardiography for the assessment of tissue reflow, they could have provided such data. It is therefore highly probable that the results would have been similar had the investigators compared either data of TIMI-2 patients: 1) with and without SFR or 2) with large and limited area at risk, or even 3) with anterior and inferior AMI.
Moreover, Yamamoto et al. (1) suggest that the higher rate of systolic/diastolic velocity ratio observed among patients without SFR could be related to the increase in arterial resistance in patients with residual thrombus burden after angioplasty. Accordingly, this difference may be related to the much higher proportion of patients presenting with right coronary artery occlusion in this subgroup. Indeed, as opposed to those of the left anterior descending, CBFV recordings show predominant systolic flow in the right coronary artery. This could have introduced a bias in the interpretation of systolic/diastolic velocity ratio between patients with SFR (93% anterior infarcts) and without SFR (82% inferior infarcts). Finally, it appears that patients with and without SFR had opposite characteristics concerning the size and location of AMI as well as the infarct-related artery. This has incontestably introduced a confounding factor in the interpretation of the study results.
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1. Yamamoto K, Ito H, Iwakura K, et al. Two different coronary blood flow velocity patterns in thrombolysis in myocardial infarction flow grade 2 in acute myocardial infarction. Insight into mechanisms of microvascular dysfunction. J Am Coll Cardiol. 2002;40:1755–1760[Abstract/Free Full Text]
2. Kawamoto T, Yoshida K, Akasaka T, et al. Can coronary blood flow velocity pattern after primary percutaneous transluminal coronary angioplasty predict recovery of regional left ventricular function in patients with acute myocardial infarction? Circulation. 1999;100:339–345[Abstract/Free Full Text]
3. Wakatsuki T, Nakamura M, Tsunoda T, et al. Coronary flow velocity immediately after primary coronary stenting as a predictor of ventricular wall motion recovery in acute myocardial infarction. J Am Coll Cardiol. 2000;35:1835–1841[Abstract/Free Full Text]
4. Yamamuro A, Akasaka T, Tamita K, et al. Coronary flow velocity pattern immediately after percutaneous coronary intervention as a predictor of complications and in-hospital survival after acute myocardial infarction. Circulation. 2002;106:3051–3056[Abstract/Free Full Text]
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