Original paper
Assessment of the efficacy of primary percutaneous coronary intervention in patients with ST-segment elevation myocardial infarction based on the ECG analysis

Introduction

Rapid restoration of the blood flow in the coronary artery occluded by thrombus is a cornerstone of treatment in patients with ST-segment elevation myocardial infarction (STEMI). Atherosclerosis is a long-lasting process consisting of progressive myocardial injury with velocity depending on the status of circulation in the particular area and around that area [1].

Results obtained in numerous angiographic studies concerning strict relation between the patency of the infarct related artery (IRA) and the evolution of myocardial infarction after reperfusion confirmed the open artery hypothesis introduced by Braunwald in 1989 [2]. According to that hypothesis, early restoration of flow in the IRA has a direct impact on the size of myocardial necrosis, on the left ventricular function and therefore on the risk of early and late mortality [3].

Restoration and maintenance of patency of the coronary artery whose occlusion led to ST-segment elevation myocardial infarction is obtained with means of thrombolysis and percutaneous coronary intervention. However, the latter method is characterized by a better efficacy defined by early and long-term results [4].

Widespread use of these methods in clinical practice required introduction of reliable and most likely non-invasive methods assessing the efficacy of treatment and prediction of the treatment results. The ECG registration has a great value for the diagnosis of arrhythmia and ST-segment changes and provides important information on the status of coronary circulation and patient prognosis [5].

Aim

The aim of the study was to assess the efficacy of reperfusion obtained by means of primary percutaneous coronary intervention of the IRA in patients with ST-segment elevation myocardial infarction based on intraprocedural ECG monitoring.

Material and methods

The study included 72 patients (64 men – 89%) with anterior STEMI admitted to the Department of Cardiologic Reanimation, Republican Research Center of Emergency Medicine of Uzbekistan Republic Ministry of Health.

The mean time between the onset of pain and admission to the Department was 2.5 ±1.3 h. The mean time between the admission and beginning of the percutaneous coronary intervention was 78.2 ±12.4 min.

The study excluded patients with a history of myocardial infarction, congestive heart failure, acute abnormalities of the cerebral circulation or left bundle branch block on ECG. Clinical characteristics of patients included in the study are presented in Table 1.

Selective coronary angiography and percutaneous coronary interventions (PCI) were performed in an operating room equipped with an X-ray system (Integris Allura FD 20. Philips). The PCI with stent implantation was an “ad hoc” procedure performed directly after diagnostic coronary angiography. Successful PCI procedure with stenting of the IRA was performed in all 72 patients (100%) after initial recanalization and pre-dilation. Good angiographic result of the procedure defined as residual stenosis < 10% was obtained in all patients. TIMI 3 flow was achieved in 62 patients (86.1%). Forty-nine patients (68%) received bare metal “Chopin” stents and the remaining 23 patients (32%) underwent implantation of paclitaxel-eluting “Luc-Chopin” stents (Balton, Warsaw, PL). The ECG registration in patients included in the study was performed using the following devices: Datex-Ohmeda (Finland), Philips IntelliVue MP20 and subsequently in the hospital room with the Shiller MT-200 device (Switzerland).

The ECG registration with monitoring of the character and frequency of arrhythmia began before the PCI. Measurement of the ST-segment changes in relation to the isoelectric line was assessed in the lead with the most pronounced changes. Assessment was performed 60 ms after the J point using the TP segment as the reference (calibration 0.1 mV/1 mm). The analysis included the altitude of the ST segment elevation in relation to the isoelectric line (maximal single lead residual ST elevation – maxSTE) and the velocity of ST-segment resolution after reperfusion. The latter parameter was calculated after determination of the difference between maximal and minimal value on the ST-segment dynamic trend in microvolts (µV) in relation to time (µV/h).

Echocardiography was performed on the Sonoline-Omnia machine (Siemens) equipped with a 4.0 MHz frequency head according to the standard methodology recommended by the American Echocardiographic Society 1, 3 and 7 days after infarction. Left ventricular end-diastolic volume (EDV) and end-systolic volume (ESV) as well as left ventricular ejection fraction (EF) were calculated in B-mode presentation according to the commonly used equation.

The scheme of antiplatelet treatment was based on the multicenter studies CURE-PCI and CREDO according to which all patients received acetylsalicylic acid (first dose of 300 mg and 75 mg/day thereafter) and clopidogrel – one dose of 300 mg 6 h before or 600 mg 2 h before PCI and 75 mg daily thereafter.

Statistical analysis

Statistical analysis was performed using the EXCEL 7.0 worksheet and STATISTICA 6.0 software for WINDOWS. All parameters were presented as the arithmetic mean (M), standard deviation (SD) or median (Me) for parameters without normal distribution. Normality of data distribution was assessed by means of the Kolmogorov test. To analyse the correlation between the analysed parameters the linear Pearson correlation coefficient was calculated.

Results

Total occlusion (TIMI flow 0) of the left anterior descending artery (LAD) was confirmed in all 72 patients. The occlusion was localized in the proximal LAD segment in 49 patients (68%) and in the median LAD segment in 23 patients (32%). All patients underwent a successful PCI procedure with LAD stenting. TIMI flow 3 was restored in 62 patients (86.1%) and TIMI flow 2 in 10 patients (13.9%). There were no deaths or complications in the form of in-stent thrombosis or distal embolization.

Analysis of the results of ECG monitoring showed characteristic dynamics of ST segment resolution. The index of ST-segment resolution velocity after PCI was 3070.3 ±946.6 µV/h. Arrhythmia from reperfusion was noted in all cases of PCI. Ventricular extrasystole (VE) occurred in 72 patients (100%), accelerated idioventricular rhythm (AIVR) in 13 patients (18%), ventricular tachycardia (VT) in 14 patients (19.4%) and ventricular fibrillation (VF) in 2 patients (2.7%). Measurement of LV systolic function showed a significant increase of the LV ejection fraction (Figure 1). LV ejection fraction was 38.9% on the first day, 51.6% on the 3rd day (p < 0.05) and 55.8% on the 7th day (p < 0.05).

Correlation analysis demonstrated a significant relation between the ST segment resolution velocity after reperfusion and LVEF on day 7 after PCI (Figure 2). The correlation coefficient was r = 0.53366 (p < 0.001). Statistical analysis included a univariate regression analysis with the use of a linear regression equation [y = a + bx; where x – independent variable, y – dependent variable, a – constant, β – regression index] to predict LVEF values based on the ST segment resolution velocity after reperfusion. In that case the linear regression equation was as follows: LVEF % = 45.772 + 0.00233 × ST segment resolution velocity (µV/h).

The coefficient of determination was r2 = 0.2848 (p < 0.0001), which allows this regression model to be used for the prediction of events.

Discussion

It is known that angiographic indices of the infarct related artery patency are not sufficient for the assessment of the efficacy of reperfusion therapy in patients with ST-segment elevation myocardial infarction [1].

Many multicentre clinical trials dedicated to development of new schemes of reperfusion therapy have questioned the faith in the absolute relation between the coronary flow assessed by coronary angiography and the size of myocardial infarction [6-8].

Coronary angiography permits one to obtain a single shot picture showing patency of the coronary artery, but the IRA may become occluded once again in the post-procedural period.

Another limitation of coronary angiography is its inability to assess microvascular circulation, which determines the true myocardial perfusion. Microvascular circulation in the infarct zone may be impaired or completely abolished despite restoration of adequate flow in the infarct related artery. Evidence of the presence of the no-reflow phenomenon after thrombolytic treatment was found by Ito et al., who examined myocardial tissue perfusion using contrast echocardiography [9]. They found that approximately 25% of patients after successful opening of the coronary artery with restoration of TIMI 3 flow presented signs of the no-reflow phenomenon. Furthermore, a relation between no-reflow and progression of early left ventricular remodelling and heart failure was demonstrated [10]. Gąsior et al. determined the risk factors of microvascular flow and the no-reflow phenomenon in patients with STEMI treated with PCI [11].

Non-invasive criteria of successful coronary artery reperfusion include rapid chest pain resolution, occurrence of arrhythmia and conduction abnormalities, rapid resolution of pathological ECG changes (at first ST-segment resolution) and accelerated dynamics of myocardial necrosis marker changes.

Standard ECG registration and ECG Holter monitoring were included in the protocols of global multicentre studies. The GUSTO-I trial assessed the value of ECG Holter monitoring in the prediction of reperfusion. A criterion of TIMI flow 2 or 3 restoration was defined as more then 50% ST-segment resolution in the most suitable lead 90 min after the procedure in comparison to baseline. It was assumed that the coronary artery undergoes reocclusion if ST-segment resolution does not reach 50% of the initial elevation or if initial resolution is replaced by new onset persistent elevation before coronary angiography [12].

Comparison of coronary artery patency 90 min and 180 min after the start of coronary angiography calculated on the basis of ST-segment dynamics demonstrated that the prognostic accuracy of this index is 74% for the diagnosis of TIMI flow 2 and 3 and 59% for TIMI flow 0-1 (mean 70%). Maximal and minimal sensitivity of this method was 92% and 75% respectively with 44-45% specificity. The accuracy of prognosis was independent from the localization of myocardial infarction.

An even more important issue is the prognostic value of ECG dynamics in terms of mortality of patients with myocardial infarction undergoing reperfusion. Besides the ISAM study, also the multicentre INJECT study compared the efficacy and safety of thrombolytic treatment in 1398 patients and demonstrated that the degree of initial ST-segment elevation resolution is a strong predictor of mortality during 35 days follow-up in STEMI [13]. Similar results were obtained in the GISSI-II, GUSTO-III and APEX-AMI studies [14, 15].

Interesting results were obtained during examination of ST-segment dynamic and survival of patients after myocardial infarction treated with primary PCI. Frequency of 3-year survival after PCI with restoration of TIMI 3 flow was 71% in case of the lack of ST-segment resolution, 86% in case of ST-segment resolution of about 30-70% in comparison to the initial elevation and 96% in case of ST-segment resolution exceeding 70% of the initial elevation [5].

Survival of patients after myocardial infarction directly depends on LV systolic function and increases with improvement of LVEF.

Experimental studies have shown that restoration of mechanical function may be markedly delayed even in the case of coronary flow restoration after a short period of ischaemia and the lack of irreversible myocardial injury [1]. This phenomenon of reversible myocardial dysfunction after an ischaemic episode despite complete restoration of myocardial oxygen supply is known as stunning.

The state of myocardial stunning occurs clinically after early reperfusion of acute coronary artery occlusion in patients with acute coronary syndrome. Reduto et al. showed that LV ejection fraction does not increase directly after reperfusion, but after discharge from the hospital in patients after intracoronary administration of streptokinase [16]. Results obtained by other researchers [17] confirmed that regional LV function reliably increases not earlier than 10 days after successful thrombolytic treatment performed 5 h after the coronary artery occlusion.

Nanto et al. used contrast echocardiography to demonstrate late restoration of LV systolic function in patients after reperfusion. The study by these authors showed that 10 of the 21 patients had late restoration of LV function [18]. Similar conclusions were reached by Wita et al. in patients treated with primary percutaneous coronary intervention [19]. Our observations show that LV systolic function is restored 3-7 days after PCI, which is related to the presence of myocardial stunning of the area supplied by the IRA. Our study sought to determine the relation between the ST-segment resolution velocity index after PCI (as a marker of successful myocardial perfusion restoration) and LVEF (as a marker of LV systolic function restoration).

The significant correlation between the indices of ST-segment resolution velocity after reperfusion and LVEF after 7 days allows one to predict the degree of LV systolic function restoration in the first hours of reperfusion.

The results confirm a high value of intraprocedural ECG monitoring for the assessment of reperfusion efficacy in patients with STEMI. These results demonstrate that ST-segment registration and analysis are necessary to assess the degree of adequate coronary artery flow restoration as well as short and long-term prognosis in patients with myocardial infarction undergoing percutaneous interventions.

Conclusions

1. Electrocardiogram monitoring has a high clinical value for the assessment of reperfusion efficacy in patients with ST-segment elevation myocardial infarction.

2. A significant correlation was found between the ST-segment resolution velocity after reperfusion and LVEF measured on day 7 after ST-segment elevation myocardial infarction.

3. ST-segment resolution velocity after reperfusion is a good predictor of LV systolic function restoration.

4. Percutaneous coronary intervention with stenting of the IRA is an effective method of reperfusion in patients with ST-segment elevation myocardial infarction.

References

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