a b s t r a c t

Introduction: Some studies suggest better outcomes after the use of thrombolytics in inferior ST- elevation myocardial infarction (STEMI) compared to other locations. The goal of this study is to compare the clinical endpoints of thrombolytic-treated STEMI based on coronary artery distribution.

Methods: The study population was extracted from the 2014 Nationwide Readmissions Data using the International Classification of Diseases, Ninth Revision, Clinical Modifications codes for STEMI, throm- bolytic infusion, and complications of STEMI. Primary study endpoints included in-hospital all-cause mortality, length of hospital stay , cardiogenic shock, and mechanical complications of STEMI. Results: A principal diagnosis of thrombolytic-treated STEMI was identified for in 1231 patients (mean age 61.5 years; 26.5% female). Four hundred and thirty-one STEMIs occurred in the left anterior descend- ing (LAD) artery distribution, 124 in the left circumflex (LCX) artery distribution, and 676 in the right coronary artery distribution. In comparison to the LAD and LCX distributions, thrombolytic- treated STEMIs in the RCA distribution were associated with lower mortality (6.5% with LAD, 5.7% with LCX, and 3.6% with RCA; p = 0.02), fewer cardiogenic shock (12.3% with LAD, 12.1% with LCX, and 7.7% with RCA; p = 0.01), and shorter LOS (4.5 days with LAD, 3.9 with LCX, and 3.6 days with RCA; p < 0.01). Mechanical complications showed no significant difference based on coronary distribution (2.3% with LAD, 3.2% with LCX, and 1.2% with RCA; p = 0.17).

Conclusions: Thrombolytic-treated STEMIs in the RCA distribution were associated with lower in-hospital

all-cause mortality, cardiogenic shock, and shorter LOS. Mechanical complications were not different based on coronary distribution.

(C) 2019

An ST-segment elevation myocardial infarction occurs approximately every 42 s in the United States [1]. Nearly 3.4% of patients die within the first 7 days, and up to 15% of elderly STEMI patients will not survive the initial hospitalization [2,3]. The pre- ferred treatment is restoring flow with percutaneous coronary intervention (PCI) within 90 min of presentation to a PCI center or 120 min from a non-PCI center [4,5]. In 2007, only 30% of STEMIs present to a PCI facility, however, a more recent percentage of STE- MIs treated with thrombolytic therapy is not well described [6]. Outcomes of PCI-treated STEMI are dependent on the location of

* Corresponding author at: One Hospital Dr. CE306, Division of cardiovascular medicine, Columbia, MO 65212, USA.

E-mail address: [email protected] (T. Enezate).

infarction [7-9]. There are limited data describing a differentiation of outcomes based on coronary location in thrombolytic-treated STEMIs, therefore, this study was conducted.

The study population was extracted from the 2014 Nationwide Readmissions Data (NRD) database which has the largest collection of de-identified hospital data in the United States with safeguards to protect the privacy of patients and hospitals. It has multiple variables for each hospital stay including International Classifica- tion of Diseases, Ninth Revision, Clinical Modification (ICD-9-CM) codes for principal and secondary diagnoses [10]. ICD-9-CM codes were used to search for a principal diagnosis of STEMI, throm- bolytic infusion, comorbidities, and endpoints of interest (Supple- mental Table 1) [11-14]. PCI-treated STEMIs and STEMIs with unspecified site were excluded.

The study endpoints included in-hospital all-cause mortality, length of stay (LOS), cardiogenic shock, mechanical complications

https://doi.org/10.1016/j.ajem.2019.04.026

0735-6757/(C) 2019

80 K. Gifft et al. / American Journal of Emergency Medicine 38 (2020) 79-82

of STEMI, bleeding, and intracranial hemorrhage. The 2014 NRD reports in-hospital mortality and mean LOS. Other endpoints were defined by the specific ICD-9-CM codes (Supplemental Table 1) [11,13-15]. Left anterior descending (LAD) distribution was defined

Fig. 1. Study population extraction process.

as anterior and/or anterolateral walls’ involvement, left circumflex (LCX) lateral, posterior, and/or posterolateral walls’ involvement, and right coronary artery inferior and/or inferolateral walls. Pearson Chi-square and unpaired-sample t-test were used to compare categorical and continuous variables, respectively. Uni- variable and Multivariable logistic regression models were used to identify predictors of mortality of thrombolytic-treated STEMIs by calculating adjusted odds ratios and 95% confidence intervals for baseline characteristics [16,17]. A two-tailed p-value of <0.05

was used for statistical significance.

There were 76,794 discharges identified with a principal diag- nosis of STEMI, 1.7% were treated with thrombolytics (Fig. 1). The mean age 61.5 years; 26.5% female (Table 1). In comparison to LAD and LCX, thrombolytic-treated RCA STEMIs were associated with significantly lower mortality, cardiogenic shock, and shorter LOS. No significant difference in terms of mechanical complica- tions, any bleeding or Intracranial bleeding (Table 2). Intracranial bleeding and cardiogenic shock were the strongest predictors of mortality. RCA distribution was associated with lower mortality, whereas LAD distribution was a predictor of increased mortality (Supplemental Table 2).

The PCI-treated RCA STEMIs have a better prognosis than other locations, with approximately a 10% mortality compared to 15.8% with left system STEMIs. The most likely explanations are the smaller size and territory supplied by the RCA (approximately 16% of left ventricular myocardium) [18-21]. Conversely, the LAD and LCX supply 50% and 34% of the left ventricular myocardium, respectively [21]. Despite the fact that LCX supplies less myocar- dium, LCX and LAD STEMIs were associated with comparable end- points likely because LCX infarcts are more often electrically silent which could lead to delayed diagnosis and emergent reperfusion, and subsequently worse endpoints [22,23]. The longer LOS noted with LAD and LCX distribution could be explained by the higher incidence of complications, such as cardiogenic shock; additionally more patients in this subpopulation qualified for surgical revascu- larization evaluation prior to discharge [21].

This study shows that RCA distribution is a predictor of better endpoints than other coronary distributions in thrombolytic- treated STEMI, and it was comparable to PCI-treated RCA STEMIs in the same 2014 NRD database. This is consistent with previous observations where the low-risk thrombolytic-treated RCA STEMIs

Table 1

Demographics, baseline characteristics and comorbidities of the overall thrombolytic-treated ST elevation myocardial infarction and by STEMI location.

LAD: left anterior descending artery, LCX: left circumflex artery, RCA: right coronary artery.

K. Gifft et al. / American Journal of Emergency Medicine 38 (2020) 79-82 81

Table 2

Endpoints of thrombolytic-treated STEMI per coronary distribution of left anterior descending artery (LAD), left circumflex artery (LCX), and right coronary artery (RCA). p-Values. A p-value of <0.05 indicates a statistically significant difference.

LOS: length of stay, SD: standard deviation.

^* This p-value assesses the difference between RCA and LAD/LCX distribution.

had comparable mortality to PCI-treated [24]. Thus, these results might suggest that, in the absence of complications, the need for transfer to PCI facility for urgent coronary angiogram might be less compelling in this subgroup.

This study also shows that LCX and LAD distributions were associated with increased in-hospital morbidity, and LAD distribu- tion was an independent predictor of increased mortality; which raises the question if LAD and LCX STEMIs should be transferred to a PCI center, even if the Transfer time is longer than recom- mended. It emphasizes that the presence of cardiogenic shock is a major predictor of death in thrombolytic-treated STEMIs, and PCI might be the preferred treatment option regardless of the transfer time [25,26].

This study is a retrospective study, and the timing and the type of thrombolytic agents could not be specified. It is unclear whether the STEMI localization used by ICD-9-CM codes was based on the electrocardiographic criteria or coronary angiogram, however, the electrocardiographic criteria of STEMI strongly correlate with angiogram [27,28]. Coronary circulation can have variation and overlap in terms of territory supplied.

Disclosures

All authors have no conflict of interest, financial disclosures or relationship with industry.

Appendix A. Supplementary data

Supplementary data to this article can be found online at https://doi.org/10.1016/j.ajem.2019.04.026.

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