Systematic review of ST-elevation myocardial infarction

¶ … door to balloon time is an important determinant of the prognosis of STEMI patients. To reduce D2B times, most centers implement a pre-hospital triage which involves the use of pre-hospital ECG to allow direct transfer of patients with confirmed STEMI to the PCI lab. Since most health facilities do not have PCI laboratories, a quick decision needs to be made regarding fibrinolytic therapy or transfer to a PCI facility. The most important factor determining this decision is the time taken from the onset of symptoms to arrival at a hospital facility and the predicted time duration for effective transfer. Through this systemic review, we sought to analyze the role of pre-hospital management in door to balloon time (D2B), door to needle (D2N) time and the long-term mortality of STEMI patients.

Since pre-hospital delay is responsible for the greatest time loss, and is indeed the most variable factor, we tried to determine the role of symptom to balloon time (S2B), or first emergency contact to balloon time (E2B) rather than door to balloon times as an important determinant to PPCI or thrombolysis.

METHOD: A total of fifty studies, of world's literature, were identified regarding STEMI. Thirty articles met our inclusion criteria and were used. The MOOSE guidelines were used to assist the review. Relevant data was used to create tables and figures, which summarized the effects of pre-hospital management.

RESULTS: All studies provided positive evidence towards a pre-hospital ECG improving D2B times and improving the overall mortality of STEMI patients. EMS transport helped in reducing D2B times when compared to private transporters due to the use of a pre-hospital ECG. However, the D2B time only accounted for 29.7% of the total time to treatment.

CONCLUSION: Since majority of the time is spent at the scene and during transport, a preferable measurement would be S2B or E2B.

BACKGROUND INFORMATION:

Myocardial infarction is an irreversible change caused by acute ischemic necrosis of an area of the myocardium. This ischemic necrosis is the result of a critical imbalance between coronary blood supply and myocardial oxygen demand. It is the most common cause of death in the United States and a leading cause of death in most developed nations. Most patients who have fallen victims to an MI are elderly; however, due to an inclining trend towards a sedentary lifestyle amongst most people, MI is beginning to appear in younger patients as well (Boon, Colledge & Walker, 2010).

The pathophysiology behind ischemic necrosis is coronary artery atherosclerosis with plaque rupture and superimposed thrombus formation. Rarely, infarction may also result from prolonged vasospasm, hypotension, excessive metabolic demand, embolic occlusion, vasculitis, aortic dissection or aortitis (Boon et al., 2010).

Transmural involvement is the more common type of infarction. In this type, more than fifty percent of the myocardial wall undergoes ischemic necrosis. Symmetrically peaked T. waves are characteristic of a transmural infarction. The T. waves are replaced with ST-segment elevation after several minutes. This type of infarction results from a complete thrombotic occlusion of a coronary artery. If the occlusion is not immediately relieved, pathological Q. waves may develop. The development of a Q. wave reflects a dead zone that has undergone irreversible injury. Subendocardial infarction is the other type of MI that involves lesser than fifty percent of the myocardium. (Boon et al., 2010)

MI is considered as part of a spectrum referred to as Acute Coronary Syndrome, ACS. This continuum represents ongoing myocardial ischemia and is divided into three broad categories: unstable angina, non-ST-segment elevation myocardial infarction (NSTEMI), and ST-segment elevation myocardial infarction ( STEMI). (Boon et al., 2010)

Unstable angina is caused by the formation of a non-occlusive thrombus in an area that is already affected with atherosclerosis. In this type, symptoms occur at rest with an increase in frequency, intensity and duration of episodes. Patients with unstable angina are at a high risk of developing MI. (Boon et al., 2010)

NSTEMI, also known as Non-Q wave infarction develops from high-grade but non-occlusive thrombi. ECG changes in NSTEMI include ST-segment depression and/or T. wave inversion without the evolution of pathological Q. waves. There may be some loss of R. waves in leads facing the infarct. ST-segment elevation myocardial infarction reflects active and ongoing transmural myocardial injury. Patients who do not develop a STEMI are diagnosed either with unstable angina or an NSTEMI. Both these conditions may or may not have ECG changes, such as ST-segment depression or morphological T-wave changes. (Boon et al., 2010)

The division of patients with either STEMI or NSTEMI also has prognostic significance. Patients with Q. wave and ST-segment changes in general have a larger area of infarction and therefore have a higher in-hospital mortality rate than with patients with NSTEMI and non-Q wave infarction. After a period of years, following an infarction, the mortality rate of NSTEMI increases, approaching that of STEMI. Therefore, it can be said that initial mortality of STEMI is higher than NSTEMI and so is the initial prognosis at the time of infarction. (Boon et al., 2010)

The recognition of symptoms of ACS is crucial for timely assessment and arrival to the hospital. It is not unusual for some patients to wait up to a few hours before calling for assistance. Reasons for this delay may be uncertainty of the severity of a specific set of signs and symptoms or fear of criticism for a false alarm. (Boon et al., 2010)

Over the last 30 years, the paradigm for the diagnosis and treatment of ACS has switched from management of complications of the disease in the critical care unit (CCU) to the detection and reversal of the pathophysiological process starting in the pre-hospital arena and continuing to the ED with the rapid transfer of selected patients to the cardiac catheterization suite.

Currently, two modes of treatment for STEMI patients are in practice. First is fibrinolytic therapy, where certain drugs are used to break up thrombus that occludes the vessel wall. The efficacy of this therapy diminishes with time. The recommended delay should not exceed beyond thirty minutes. (Harding, Mangini & Taunton, 2010)

Percutaneous coronary intervention is another mode of therapy for STEMI patients. This mode is regarded to be better in terms of clinical outcome and the thirty day patient mortality and morbidity. PCI is a non-surgical procedure in which a cardiac catheter with a balloon is inflated into a blocked artery. This restores the arterial lumen. The balloon is removed and a stent is placed in order to keep the lumen patent. According to current guidelines, the time for PCI should not exceed beyond 90 minutes from the onset of symptoms. (Harding et al., 2010)

Many health care setups do not contain facilities for PCI. These patients could be transferred to a hospital that contains a PCI laboratory or they could be managed using fibrinolytic therapy. The delay that maybe created in the transfer needs to be carefully analyzed by the emergency facility. In any case, this delay should not exceed beyond ninety minutes. Based on several researches, the ACC/ACH has also devised guidelines that minimize this delay. (Harding et al., 2010)

The management and outcome of patients with STEMI greatly depends on door to balloon, D2B or D2N time, which in turn depends on several factors, such as: time lapse from the onset of symptoms to Emergency Medical Service, EMS, call; time lapse from the EMS call to its arrival; and the time from first medical contact to balloon inflation.

The door to balloon time can also differ for patients arriving through private transport or through an emergency medical service. Several studies reveal that even though private transport can be quicker, the door to balloon time is considerably shorter for patients using an EMS. A pre- hospital ECG is one factor that shortens this time. Communicating necessary findings on an ECG or characteristic symptoms through a paramedic to the emergency facility minimizes ER stay, allowing quicker transport to a PCI facility. Also, direct arrival of an EMS service to a PCI laboratory enables to shorten the delay caused from transporting a STEMI patient from a STEMI referring facility to a STEMI accepting hospital that contain PCI facilities. (Boon et al., 2010)

Helicopter Emergency Medical Service, HEMS, can be used for faster transport, in cases where land EMS cannot reach on time. Data on the usefulness of this mode of transport is relatively less as compared to land EMS.

REVIEW OF CURRENT GUIDELINES:

Due to the crucial role of door to balloon time in the prognosis of patients with STEMI, and compiling clinical studies regarding different protocols, clinical guidelines have changed almost annually for the past few years. The advantage of these guidelines and updates is that they have critically analyzed and compiled extensive amount of information available through research and clinical trials, and have provided evidence-based recommendations necessary for management.

Current guidelines state that patients who develop symptoms of ACS should be immediately transferred to the emergency department or to a facility that is capable of acquiring a 12 lead ECG as well biomarkers. These patients should not be evaluated over the telephone. The preferable mode of transport to the emergency department should be via an EMS rather than with private transport. (Harding et al., 2010)

In order to minimize the delay, patients are advised not to repeat a second dose of nitroglycerine if the pain persists. (Harding et al., 2010) Instead, an EMS should be contacted immediately and an additional two doses, at fifteen minute intervals, can be taken while waiting for EMS arrival. Current protocols also advocate the use of a pre-hospital ECG in order to distinguish STEMI patients for immediate transfer to PCI facilities. (Harding et al., 2010) For patients who do not have ST segment or T. wave changes, a repeat ECG after twenty minutes is advised. Serial ECGs in the emergency department are also recommended for evolutionary changes that are not initially apparent.

These guidelines also provide insight to the dilemma of whether to transfer high risk PCI candidates to PCI centers from non-PCI centers. The new Class 11 recommendation is that it is reasonable for such high risk PCI candidates, who have received fibrinolytic therapy, to be immediately transferred to PCI receiving centers from PCI referral centers. (Preeti, 2011) PCI will then be performed as needed or as a pharmaco-invasive strategy. These recommendations also favor initiating a preparatory anti-thrombotic regimen before and during transfer to a PCI facility. (Preeti, 2011)

OBJECTIVE:

To analyze the effect of pre-hospital management of ST-segment elevation myocardial infarction on door to balloon times and long-term patient mortality.

Method and Material:

A systematic review was performed on the relevant literature available regarding the role of pre-hospital management on the outcome of STEMI patients. First, a thorough read was given to the subsequent changes in the protocols from the year 2007 and onwards regarding STEMI management.

A list of factors affecting pre-hospital delay was first identified. These factors included: time of onset of symptoms to EMS call, time from call to EMS arrival, transport time, time delay at the Emergency department and activation of concerned team and finally time taken during transfer of patients to PCI lab to the inflation of balloon.

The meta-analysis of observational studies in epidemiology group, MOOSE, guidelines was used to assist the review. (Stroup et al., 2008) A total of fifty articles were identified using the PUBMED, GOOGLE SCHOLARS and UPTODATE database. Keywords used to assist the search included, "Pre-hospital management," "Pre-hospital triage," "STEMI," "EMS vs. Private transport," "role of 12 lead ECG," "Pre-hospital protocol" and "Bypass of non-PCI centers."

All articles that discussed pre-hospital management of STEMI and factors affecting it were included in the systemic review. Also, studies were included only if they reported data on adults (> 18 years) who were diagnosed with acute STEMI, experienced chest pain for less than 12 hours and were identified by EMS personnel in the pre-hospital environment. Articles that compared EMS service to private transport were also used. A few studies analyzed the effectiveness of certain protocols for pre-hospital management of STEMI and were also considered. Articles that were published after the year 2009 were preferred. Studies conducted from each continent were included in the analysis.

A quality appraisal tool was used to evaluate the credibility, rigor and relevance of each study. (Public Health Resource Unit, 2006) After a thorough read of each article, the title, author names and institutional affiliations were blinded to the author and the sequence was jumbled. All citations of each article were reviewed independently in a hierarchical manner. The quality appraisal tool was then used to evaluate relevance, credibility and rigor. Each article was then classified under either "INCLUDE" or "DISCARD." A total of thirty studies were chosen in this manner.

The time duration, target population, number of subjects per article, study method and any other consideration for each article was then summarized. A summary of this is provided below. Each of the factors studied in each research were then identified and its effect on door to balloon time and 30 day mortality was calculated and evaluated on tables and figures using Microsoft Excel.

Factors predicted to affect D2B, D2N and overall mortality of STEMI patients were: use of 12 lead ECG in a pre-hospital setting, EMS verses Private transport of patients, patients presenting to the ED during off-hours, bypass of non-PCI centers for patients with confirmed STEMI and activation of PCI labs and concerned teams by the EMS.

Most studies divided the D2B time into: Decision to seek care using private vs. EMS; Decision to seek care -- hospital arrival; Decision to seek care -- reperfusion therapy; Symptoms -- reperfusion therapy. The eligibility criteria for patients undergoing primary PCI were: symptom duration of 12 hours or less and ST-segment elevation of 0.1 mV or greater in at least 2 contiguous leads (0.2mV in V1-V3) or presumed new-onset left bundle-branch block.

Out of a total of thirty published studies that were used for this systemic review, eighteen articles and two meta-analyses were identified to have analyzed the effect of pre-hospital triage on door to balloon time, door to needle time and over-all mortality of STEMI patients. A sum of 14327 patients met the inclusion criteria. The sample was a good representative of populations from the United States, Australia, Qeubec, New Zealand, Canada, Switzerland, Amsterdam, Lebanon and Denmark. Seven out of the eighteen researches were conducted using a data base for national records and contributed to a comparatively greater sample size. These researches represented the following locations: Western Denmark, Netherland, the United States and Quebec. Most of the articles identified were pre and post interventional designs based on a single hospital.

A great majority of studies evaluated the effectiveness of a pre-hospital triage. The pre-hospital triage advocates the use of a pre-hospital ECG, thus allowing activation of PCI labs prior to patient arrival and direct transport of confirmed STEMI patients to PCI facilities. These articles analyzed the effect of bypassing non-interventional facilities and the emergency department through pre-hospital ECG and its interpretation by paramedics or its transmission to the on-call emergency team. The efficacy of transmission was also analyzed by one study that was conducted in Australia.

A meta-analysis study of 2264 citations identified 980 patients that were directly transferred to a PCI lab (Brooks et al., 2009). Ten other studies and one meta-analysis that were conducted on the usefulness of pre-hospital triage were used to formulate results and draw a conclusion.

One study, conducted in a rural set up, investigated the efficacy of thrombolytic treatment prior to transport to PCI facilities (Crowder et al., 2011). A similar research, conducted on transfer of STEMI patient, evaluated the practicality of transfer of patients from non-PCI to PCI facilities.

A separate study was conducted to evaluate the usefulness of 'Code STEMI' in reducing the D2B time (Bajaj et al., 2011). The Code STEMI was established to produce better results for STEMI patients who presented in "off hours." Off hours were described to be weekday nights, weekends and official holidays. In this study, patients were divided into two groups. The first group consisted of 27 STEMI patients that presented to the hospital during off hours before the Code STEMI was operational (January -- December 2006). The second group included 60 patients who presented to the hospital during off hours when Code STEMI was fully functional. (January 2007 -- December 2008) A similar study identified the usefulness of a STEMI care system from January 2008 to December 2010. This was a prospective observational study that included a pre-hospital ECG by paramedics.

One study evaluated the effectiveness of ECG transmission from ambulances using computerized Glasgow algorithm to two cardiologists as part of the pre-hospital triage. The efficacy of transmission, sensitivity and specificity of interpretation was calculated. Two similar studies evaluated transmission time as part of pre-hospital delay.

Out of the eighteen studies conducted, six analyzed the popularity of EMS amongst the general population. The quickness of EMS was also compared to Private transport. A total of 15541 STEMI patients were identified that presented to the ED through either EMS or Private transport. The studies that were chosen in this meta- analysis were from different parts of the world, namely, The United States, Canada, the Gulf countries, Sweden and China.

One study that was conducted in Ottawa from July 2001 to January 2004 used the Ottawa Hospital STEMI registry to prospectively collect results on all STEMI patients (So et al., 2006). This study analyzed the use of EMS (as compared to Private transport) and its relationship to treatment, morbidity and mortality of STEMI patients.

A study was conducted using data from the Rapid Early Action for Coronary Treatment Trial (REACT- Trial). This trial used data from 20 different cities in the United States (Aghari et al., 2011). Elapsed travel times were ranked within Zip Codes and submitted to a nested analysis of variance model to determine if elapsed time was different for the different modes of transport.

A similar prospective, observational study was conducted to determine the time for an EMS service to respond to a 911 call (Qiu et al., 2011) Two groups were used in this study. A rapid dispatch protocol was used for the first group. In this protocol, the emergency medical dispatchers were asked to confirm the caller's phone number and address and to ask if there was a medical emergency, and then to dispatch the closest ambulance.

Another study conducted in China from 1st November 2005 -- 31st December 2006, was a prospective, cross-sectional study that included 19 hospitals in Beijing (Song, Yang & Hu, 2010). This was a comparative study based on the quickness of EMS vs. Private transport.

A similar study was conducted in 2007, in sixty five centers located in six Arab Gulf States (Fares et al., 2011). The results were obtained from the Gulf Registry of Acute Coronary Events (Gulf RACE). Results were separated based on the mode of presentation to the ER. All of the above mentioned studies evaluated the efficacy of the emergency Medical Service vs. Private transport.

A separate study from Stockholm was conducted to evaluate the popularity of EMS amongst patients with AMI (Thuresson et al., 2008). Records for 3805 patients from 11 medical centers, in greater Worcester, were viewed for the years 1997, 1999, 2001 and 2003.

A separate set of articles evaluated the feasibility of HEMS for transport of STEMI patients. A case review on the subject matter was written in which a 40-year-old lady called 911 with typical complaints indicative of a myocardial infarction. (Palmer, McMullen, Knight, Gunderman & Hinkley, 2011) An EMS service was recruited to her house 14 minutes following the call. Air service was requested to arrive at the cardiac scene 6 minutes later for rapid transport to a PCI facility. The closest PCI facility was 35 minutes away by land and 13 minutes by air. The closest non-PCI facility was 20 minutes away from ground. Another retrospective study reviewed records of HEMS inter-facility transport time to PCI facilities in the year 2009. (Higgins, Kendali & Baumann, 2011)

RESULTS:

Ten studies discussed the effect of bypassing the ED on D2B times. This was possible through pre-hospital ECGs that were either transmitted to the on -- call resident or were interpreted by the paramedics themselves. The confirmation of STEMI allowed the activation of the PCI lab and team. The results of the meta-analysis showed that a pre-hospital triage enabled STEMI patients to have D2B times lesser than the acceptable range (Figure 1).

D2B with a pre-hospital ECG

Study conducted (Figure 1)

A (Adams et al., 2011); B (Chughtai et al., 2011); C (Qui et al., 2011); D (Lambert et al., 2011); E (So et al., 2006) F (Camp-Rogers et al., 2011) G (Grosgurina et al., 2010) H (Cheskes et al., 2011); I (Hanna, Hennebry, Abu-Fadel, 2010); K (Terkelsen et al., 2010); L (Song, Yang & Hu, 2010)

Figure 1:

This figure shows that with the use of pre-hospital ecgs and bypassing the ED, door to balloon times were reached within the accpetable time (less than 90 minutes), with the shortest being 7.69 minutes in study F. And the longest being 79 minutes and an average of 46.67 minutes.

Out of the ten studies conducted on the relationship of pre-hospital triage with D2B times, seven articles displayed results of D2B times before and after the implementation of pre-hospital ECGs. The results reveal a considerable difference in D2B times regarding the effect of pre-hospital management (Figure 2).

A number of studies also provided the total time from onset of symptoms to ballooning and the time taken from the first emergency contact to balloon inflation. Analysis of this group of articles revealed that most of the time is spent at the scene and during transport (D2B representing a mean of 29.7% of the total time to treatment). (Table 1)

Study

Symptom to Balloon

Door to Balloon

Emergency Contact to Balloon

A

36

B

52

Not Mentioned

C

54

99

D

Not Mentioned

44

36

E

43

Not Mentioned

H

Not Mentioned

35

70

K

61

Not Mentioned

L

(Table 1)

A (Adams et al., 2011); B (Chughtai et al., 2011); C (Qui et al., 2011); D (Lambert et al., 2011); E (So et al., 2006) F (Camp-Rogers et al., 2011) G (Grosgurina et al., 2010) H (Cheskes et al., 2011); I (Hanna, Hennebry, Abu-Fadel, 2010); K (Terkelsen et al., 2010); L (Song, Yang & Hu, 2010)

Table 1:

Shows that the door to balloon times of STEMI patients in all the studies fall within the 90 minute range except for 2 outlyers, study L. And M. However, the major variation is seen amongst Emergency contact to balloon times which ranges from 36 to 173, also including studies that have not mentioned Emergency contact to balloon times. This shows lack of awareness of the importance of E2B time. This is a crucial period in determining the outcome of the patient as it is the time from which the emergency system is activated and prehospital management is started, which can potentially decrease delay in receiving treatment and may improve long-term mortality. This table also mentions symptom to balloon time but is not relevant as this time is recorded by the patient (increasing chances of bias).

Acceptable D2B time

D2B time

Study conducted

RED: D2B time without a pre-hospital triage

BLUE: D2B with a pre-hospital triage

(Figure 2)

This figure shows door to balloon times with (blue) and without (red) pre-hospital management, concluding that pre-hospital management helped reduce the door to balloon times significantly in each study.

The results provided above were backed by 2 meta-analysis that also showed a decreased D2B time with direct transport of STEMI patient to PCI labs. In another study that evaluated the usefulness of a STEMI care system, the median D2B and EMS contact to hospital arrival times progressively decreased as more pre-hospital ECG's increased. (Eckstein, R & Koenig, 2011)

The study conducted on CODE STEMI shows an improvement of D2B time by 52 minutes and a decrease of 16 minutes in the ECG to PCI time (Bajaj et al., 2011). In another study, improvements of D2B times with the use of pre-hospital triage were independent of presentation during peak hours (Camp-Rogers et al., 2011). The relationship of the long-term mortality rate with total delay in treatment (Terkelsen et al., 2010) is summarized in the figure below. (Figure 3)

30- day mortality

Time delay (Figure 3) (Terkelsen et al., 2010)

Figure 3 reveals that there is an increase in 30 day mortality in patients on whom treatment was delayed, emphasizing the importance of early detection of STEMI through pre-hospital management, bypassing the ED, and early transport to a PCI facility.

The sensitivity and specificity of diagnosing STEMI and NSTEMI in a pre-hospital setting was 86% and 93%, respectively (Aghari et al., 2011). The transmission times, identified in two separate studies, for ECG transmission were 17 (Adams et al., 2011) and 10 (Chughtai et al., 2011) minutes, respectively.

As consistent with available evidence, one study showed that emergency nurses, emergency physicians, cardiology residents and consultants were confident of the paramedic's capability of interpreting pre-hospital ECGs (Rajabali, 2009). They were content with the use and quality of the technological assistance available to expedite STEMI confirmation by a physician including a pre- hospital ECG and mechanism of transmission However, emergency physicians and paramedics did recall instances of ECG transmission failure to the response-line.

Doubts were raised concerning the ability of rural paramedics to provide PHM. This concern was similar to results obtained from a study conducted by Rajabali, et al. (2009). This similar study provided contradicting evidence of a physicians' view regarding direct transfer. Results showed that about 54% of physicians felt that all pre-hospital diagnosed STEMI patients, requiring PCI intervention, should be first assessed in the ED. (Rajabali et al., 2009)

Studies that were conducted to compare EMS with Private transport revealed shorter D2N/D2B times for patients arriving through EMS, when compared to patients arriving privately.The average D2N times for two studies were 42 vs. 57 (So et al., 2006) and 32 vs. 49 (Hutchings et al., 2004), respectively. The average D2B time in 2 studies, for patients arriving through EMS and Private transport, were 124 vs. 154 (So et al., 2006) and 57 vs. 112 (Qui et al., 2011), respectively. The time for the first ECG from the onset of symptoms for patients arriving with EMS was also shorter, 11 minutes compared to 22 minutes for patients arriving with self-transport (So et al., 2006). Despite shorter D2N, D2B and symptom- first ECG times, hospital arrival was shorter for Private transporters (35 minutes) as compared to EMS (50 minutes). (Song, Yang & Hu, 2010)

The next study, representing the Arab Gulf States showed that EMS was not a popular mode of presentation of STEMI patients (Fares et al., 2011). Only 17% of patients with chest pain chose EMS. The study from Stockholm identified factors that prevent STEMI patients from utilizing EMS (Thuresson et al., 2008). Patients who arrived via private transport believed that they could get to the hospital faster with it or did not think they were sick enough. Patients using the EMS were more aware about the importance of seeking urgent medical help in case of any symptom that may point to AMI.

The study that was done on HEMS for inter-facility transport revealed an acceptable mean D2B time of 90 minutes (Higgins et al., 2011). The case review that was compiled regarding the 40-year-old female complaining of chest pain, revealed a delay of 106 minutes from the time she dialed 911 and 92 minutes for D2B time (Palmer et al., 2011).

DISCUSSION:

According to the 2010 guidelines formulated by the American College of Cardiology / American Heart Association, ACC/AHA, the D2B time should not exceed beyond 90 minutes (Harding et al., 2010). All of the articles were found to support the role of pre-hospital triage as a method of reducing D2B times. This allows the bypass of the ED for confirmed STEMI patients. Although a direct comparison of the literature regarding pre-hospital ECG and activation of PCI labs is complicated by the diverse methods of implementation, the universal reduction in D2B is robust irrespective of the method used. The drawback involved in pre-hospital activation is false alarm activation, which in two separate studies was shown to be 11% (Cheskes et al., 2011) and 12.4% (Grosgurina et al., 2010), respectively..

Although private transport proved to be a quicker mode of transport, a greater percentage of patients arriving through EMS were able to achieve recommended D2B times when compared to patients arriving privately. Therefore, EMS should be the recommended mode of transport for STEMI patients. The use of air medical transport has also shown reduced transportation times, and could be the preferred mode of transport for inter-hospital transfer or for patients for who anticipated land transport time is greater than the maximum transport time possible. Air medical transport, however, may not be possible in all situations.

The relationship between reperfusion and patient outcomes is also well established, although early PCI is the optimal treatment for STEMI. However, patients in rural areas are often located considerable distances from local hospitals, and even greater distances from PCI centers. Therefore, for rural populations, pre-hospital thrombolysis, within 30 minutes, may be the most appropriate treatment. Also, patients undergoing PPCI, a loading dose of thienopyridine should be administered to all STEMI patients, according to class 1 recommendations (Preeti, 2011).

Even though D2B times have been the focus of a majority of studies, the major proportion of time is spent at the scene. Also, the greatest variation in the total time to treatment is due to pre-hospital delay. The D2B time accounts for an average of 29.7% of the total time, as identified through an average of the studies represented in the graphs. Since the total time to treatment may not be easy to calculate in many cases, the more appropriate variable to use instead of D2B time is E2B time. E2B time is the time duration from the first medical contact (which in many cases is the time of EMS arrival) to balloon inflation. The E2D time (first medical contact to door time) can be freely communicated by paramedics to the receiving health care personal.