|Year : 2015 | Volume
| Issue : 6 | Page : 702-706
Influence of time to treatment and other risk factors on infarct size and transmurality in the case of ST-elevated myocardial infarction managed by primary angioplasty and assessed by delayed enhancement magnetic resonance imaging
Anil Kumar1, Ramanjit Singh Akal2
1 Department of Medicine and Cardiology, Base Hospital, Army College of Medical Sciences, New Delhi, India
2 Department of Medicine, Air Force Hospital, Hindan, Ghaziabad, Uttar Pradesh, India
|Date of Web Publication||19-Nov-2015|
Department of Medicine, Base Hospital, Army College of Medical Sciences, New Delhi
Source of Support: None, Conflict of Interest: None
Objectives: To evaluate the association between time to treatment and to check the effect of various risk factors such as diabetes mellitus, hypertension (HTN), smoking, family history of coronary artery disease (CAD) and obesity on infarct size (IS), transmurality and ST-segment resolution (STR) with DE-MRI (delayed enhancement magnetic resonance imaging) on 3-month follow-up in patients treated for ST-elevated myocardial infarction (STEMI), with primary percutaneous coronary intervention (PPCI). Background: Early PPCI decreases IS and transmurality but increases STR. Materials and Methods: Fifty consecutive patients with STEMI treated with reperfusion therapy in the form of PPCI and underwent cardiac MRI at 3-month interval follow-up. The primary endpoint is final IS and transmurality as assessed by DE-MRI at 3-month follow-up. Results: IS and transmurality increase and STR decreases with increase in duration to percutaneous coronary intervention from the onset of symptoms. Similarly, the effect of various confounding factors such as diabetes mellitus, HTN, smoking, family history of CAD and obesity on IS, transmurality and STR was assessed which did not affect immediate prognosis during treatment. Conclusion: Primary angioplasty is the treatment modality of choice in the case of STEMI when available. Time to treatment directly influences STR, final IS and transmurality, that is, the earlier the intervention done, more will be STR and lesser will be final IS and transmurality. There is no significant effect of confounding variables such as cardiac risk factors except family history of CAD on immediate prognosis during treatment.
Keywords: Infarct size, primary percutaneous coronary intervention, ST-elevated myocardial infarction, time to treatment, transmurality
|How to cite this article:|
Kumar A, Akal RS. Influence of time to treatment and other risk factors on infarct size and transmurality in the case of ST-elevated myocardial infarction managed by primary angioplasty and assessed by delayed enhancement magnetic resonance imaging. Med J DY Patil Univ 2015;8:702-6
|How to cite this URL:|
Kumar A, Akal RS. Influence of time to treatment and other risk factors on infarct size and transmurality in the case of ST-elevated myocardial infarction managed by primary angioplasty and assessed by delayed enhancement magnetic resonance imaging. Med J DY Patil Univ [serial online] 2015 [cited 2020 Nov 28];8:702-6. Available from: https://www.mjdrdypu.org/text.asp?2015/8/6/702/169879
| Introduction|| |
Patients with symptoms suggestive of an acute myocardial infarction (MI) and having electrocardiographic evidence of an acute MI manifested by ST elevations is considered to represent ischemia are candidates for reperfusion therapy with either primary percutaneous coronary intervention (PPCI) or fibrinolytic therapy. Patients with typical symptoms in the presence of a new or presumably new left bundle branch block or a true posterior MI are also considered eligible. If performed in a timely fashion, PPCI is the reperfusion therapy of choice compared to fibrinolysis because it achieves a higher rate of TIMI 3 flow (more than 90%), does not carry the risk of intracranial hemorrhage, and is associated with improved outcomes. The time to onset of reperfusion therapy is a critical determinant of outcome with both PPCI and fibrinolysis.
PPCI has emerged as the preferred therapy for acute ST-segment elevation myocardial infarction (STEMI). Multiple randomized trials and a recent meta-analysis have shown that PPCI lowers mortality, stroke, and recurrent MI rates compared with fibrinolytic therapy, even when patients initially present to community centers and require transfer to centers with PPCI capabilities. 
Myocardial salvage and limitation of IS expansion are the principal mechanisms by which patients with STEMI benefit from reperfusion.  The time to treatment mainly determines the outcome of patients treated by fibrinolysis or PPCI with respect to the above-mentioned parameters. , A simple method to assess reperfusion is a measurement of early ST-segment resolution (STR).  This method allows for the prediction of myocardial salvage and final infarct size (IS) measured by single photon emission computed tomography (SPECT), and subsequently of left ventricular (LV) function and clinical outcome after both fibrinolysis and PPCI. ,, Delayed enhancement magnetic resonance imaging (DE-MRI) is a relatively new imaging method for IS assessment with high spatial resolution, which in contrast to SPECT allows to discriminate transmural and subendocardial infarcts.  Both acute and chronic infarcts can be differentiated with precise location and extent of infarction. Infarct sizing is precise and highly reproducible, with minimal interobserver and intraobserver variability. Imaging is typically performed 10-20 min of intravenous injection of 0.1-0.2 mmol/kg of gadolinium chelate. 
| Materials and Methods|| |
Fifty consecutive cases of acute STEMI who had presented to Command Hospital Air Force Bengaluru from August 1, 2010 to August 31, 2012 and were treated with primary angioplasty were considered for the study. The inclusion/exclusion criteria were as follows: Patients with STEMI as defined by the standard American Heart Association criteria were taken, whereas those with contraindications to MRI and serious unrelated disease (e.g., advanced malignancy, surgery or trauma) which could limit life expectancy to less than the 90-day follow-up period were excluded. These patients were divided into two groups: Group 1 consisted of patients who underwent primary angioplasty within 6 h of onset of symptoms, whereas Group 2 consisted of patients who underwent primary angioplasty after 6 h of onset of symptoms. Data were analyzed using three variables:
- Predictor variable, that is, time to treatment from the onset of symptoms to primary angioplasty.
- Outcome variable, that is, IS, transmurality and STR.
- Confounding variables such as diabetes mellitus, hypertension (HTN), smoking, family history and obesity.
All participants gave written informed consent to the study protocol, which was approved by the ethical committee of the hospital. All patients underwent DE-MRI at 3 months follow-up interval after PPCI.
Magnetic resonance imaging protocol
IS was determined at 3-month follow-up by MRI. Imaging was performed on a 1.5 Tesla Siemen's (Siemens Medical Systems, Erlangen, Germany) MRI system. Cardiac MRI was performed using nonferromagnetic electrocardiogram (ECG) electrodes. The 3 mm slice thickness black blurred and white blurred sequences were used for assessing the morphology. A steady-state free precession 21 technique gradient sequence along with myocardial tagging was used for the kinetic study. Only 10 ml of intravenous gadolinium was used for assessing myocardial viability. Vendor provided software was used for myocardial segmentation.
The analysis was done with Statistical software SPSS 15.0, International Business Machines (IBM), Chicago, USA. Microsoft Word and Microsoft Excel by Microsoft Corpn have been used to generate graphs and tables. Descriptive statistics and ranges were computed for continuous measures, while categorical measures were presented as frequency.
| Results|| |
The study was conducted on 50 patients who were between 20 and 70 years. The baseline patient characteristics, cardiac MRI and ECG findings were given in [Table 1] and [Table 2].
| Discussion|| |
Comparison of the IS revealed 44.1% in Group 1 and 6.3% in Group 2 had IS <20% with P < 0.009 and odds ratio (OR) = 0.08, 0% had infarct in Group 1 and 43.8% in Group 2 had IS >40% with P < 0.001, which are highly significant. 56% of patients in Group 1 and 50.5% in Group 2 had IS between 20% and 40% with P = 0.767 and OR = 0.78 which is not significant. Eight patients who underwent PPCI within 6 h had no IS or transmural involvement (aborted MI) which shows early PPCI may result in aborted MI. 
Comparison of the data related to transmurality showed that 44% of patients in Group 1 and 0% patients in Group 2 had transmurality <20% with P < 0.001. Similarly, 0% patients in Group 1 and 19% in Group 2 had transmurality >50% with P = 0.029, both of which are highly significant stating that delay in percutaneous coronary intervention (PCI) from onset of symptoms results in increased transmurality. About 56% of patients in Group 1 and 81% of patients in Group 2 had transmurality between 20% and 50% with P = 0.117 which is not significant but has OR = 3.42, showing positive association between delay in treatment and increase in transmurality.
A similar study done by Thiele et al. also revealed that every 30 min delay in time to PCI increases transmurality and IS.  Comparison of the data for STR with duration to PCI showed that 2.9% of patients in Group 1 and 37.5% in Group 2 had STR <50% with P = 0.003** which is highly significant and OR = 19.6 suggest that transmurality increases 19.6 times more who presented >6 h of onset of symptoms. Similarly, 32.4% of patients in Group 1 and 0% patients in Group 2 had STR >75% with P = 0.027* which is significant. About 64.7% of patients in Group 1 and 62.5% of patients in Group 2 had STR between 51% and 75% with P = 1.0 which is not significant. In the same study by Thiele et al., they had proved that early and complete STR results in reduced IS and transmurality with final better outcome [Table 3].
On checking the effect of confounding factors (cardiac risk factors) such as diabetes, HTN, smoking, and obesity with duration of PPCI, it was found out that 38.2% of patients had diabetes mellitus in Group 1 and 50% of patients had diabetes mellitus in Group 2 with P = 0.432 and OR = 1.61 indicating an insignificant but positive association between diabetes mellitus and duration of PCI, that is, diabetes mellitus is 1.6 times more common in those who are undergoing PPCI after 6 h of onset of symptoms. Study done by Zijlstra et al. also revealed delayed presentation for PPCI with increase in incidence of diabetes mellitus [Table 4]. 
|Table 4: Association of cardiac risk factors with IS, transmurality and STR|
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Similarly, the confounding effect of diabetes mellitus while comparing both groups in relation to transmurality (P = 0.034), IS (P = 0.194) and STR (P = 0.424) was checked which revealed an insignificant association of diabetes mellitus with outcome variables except transmurality. Study done by Thiele et al. also shows relation of diabetes mellitus with transmurality, IS and STR as insignificant.
Similar comparison of the association of HTN with duration of PCI showed that 44.1% of patients of HTN in Group 1 and 56.3% of patients in Group 2 with P = 0.423 and OR = 1.63 indicating insignificant but positive correlation between the HTN which is 1.63 times more common in those who are undergoing PCI after 6 h of onset of symptoms. The confounding effect of HTN was considered by comparing both groups for transmurality (P = 0.056), IS (P = 0.408) and STR (P = 0.670). Analysis revealed no significant confounding effect of HTN on outcome variables. Study done by Thiele et al. also shows no significant association between HTN and transmurality, IS and STR.
Consideration of the confounding effect of smoking on duration of PCI showed that 67.6% of patients in Group 1 and 75% of patients in Group 2 with P = 0.597 and OR = 1.43 indicating insignificant but positive correlation, suggesting that smoking is 1.43 times more common in those who are undergoing PCI after 6 h of onset of symptoms. The confounding effect of smoking on transmurality (P = 0.286), IS (P = 0.577) and STR (P = 0.966) revealed no significant confounding effect of smoking on outcome variables. Similar results have been reported by Thiele et al.
Considering confounding effect of obesity with duration of PCI, 29.4% of patients in Group 1 and 25% of patients in Group 2 had obesity with P = 0.736 and OR = 0.80 indicating insignificant but negative association, that is, obesity is 0.8 times less common in those patients who presented after 6 h of onset of symptoms. While checking the confounding effect of obesity on transmurality (P = 0.337), IS (0.058) and STR (0.998), it was noted that there was no significant association between obesity and outcome variables.
Considering family history of coronary artery disease (CAD) and its confounding effect on the duration of PCI, it was observed that 32.4% of patients in Group 1 and 62.5% of patients in Group 2 had family history of CAD with P = 0.044 and OR = 1.49 indicating significant and positive association between family history of CAD, that is, family history of CAD is 1.49 times more common in those who presented >6 h of onset of symptoms. While checking confounding effect of family history of CAD on transmurality, that is, (P = 0.012), IS (P = 0.006) and on STR (P = 0.009) which is highly significant, the same was not evaluated in study by Thiele et al.
| Conclusion|| |
Primary angioplasty is a treatment modality of choice in the case of STEMI when available. Time to treatment directly influences STR, final IS and transmurality, that is, the earlier the intervention done, more will be STR and lesser will be final IS and transmurality. There is no significant effect of confounding variables like cardiac risk factors on final outcome variables such as LV IS, transmurality and STR except by family history of CAD. Thus, the present results verify the first hypothesis, whereas the second is not supported. It is evident that time to treatment is the most important determinant of prognosis in CAD. The confounding variables might play a part in the etiology of the disease but do not appear to contribute significantly to the immediate prognosis after onset of MI.
| Limitation|| |
The number of patients was limited as being a defense hospital only defense personnel and their dependents are entitled for treatment.
Financial support and sponsorship
Conflicts of interest
There are no conflicts of interest.
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[Table 1], [Table 2], [Table 3], [Table 4]