Article, Cardiology

Does cardiac catheterization laboratory activation by electrocardiography machine auto-interpretation reduce door-to-balloon time?

a b s t r a c t

Objectives: In an attempt to begin ST-segment elevation myocardial infarction treatment more quickly (referred to as door-to-balloon [DTB] time) by minimizing preventable delays in electrocardiogram (ECG) interpretation, cardiac catheterization laboratory (CCL) activation was changed from activation by the emergency physician (code heart I) to activation by a single page if the ECG is interpreted as STEMI by the ECG machine (ECG machine auto-interpretation) (code heart II).

We sought to determine the impact of ECG machine auto-interpretation on CCL activation. Methods: The study period was from June 2010 to May 2012 (from June to November 2011, code heart I; from December 2011 to May 2012, code heart II). All patients aged 18 years or older who were diagnosed with STEMI were evaluated for enrolment. Patients who experienced the code heart system were also included. Door-to-balloon time before and after code heart system were compared with a retrospective chart review. In addition, to determine the appropriateness of the activation, we compared coronary angiography performance rate and percentage of STEMI between code heart I and II.

Results: After the code heart system, the mean DTB time was significantly decreased (before, 96.51 +- 65.60 minutes; after, 65.40 +- 26.40 minutes; P = .043).

The STEMI diagnosis and the coronary angiography performance rates were significantly lower in the code heart II group than in the code heart I group without difference in DTB time.

Conclusion: Cardiac Catheterization laboratory activation by ECG machine auto-interpretation does not reduce DTB time and often unnecessarily activates the code heart system compared with emergency physician- initiated activation. This system therefore decreases the appropriateness of CCL activation.

(C) 2014

  1. Introduction

Acute myocardial infarction is a common disease with a high mortality in the emergency department (ED). Early intervention is fundamental to the successful treatment of ST-segment elevation myocardial infarction , as the timely restoration of Coronary blood flow can reduce mortality [1,2]. The American College of Cardiology, the American Heart Association, and the European Society of Cardiology guidelines recommend that a patient presenting to the ED with STEMI should receive fibrinolytics within 30 minutes of arrival or percutaneous coronary intervention (PCI) within 90 minutes of arrival (door-to-balloon time [DTB] time) [3-5].

* Corresponding author. Pusan National University Yangsan Hospital, Beomeo-ri, Mulgeum-eup, Yangsan-si, Gyeongsangnam-do, 626-770 South Korea. Tel.: +82 55 360 2143; fax: +82 55 360 2173.

E-mail address: [email protected] (J.H. Ryu).

Recently, many studies have proposed different strategies to reduce DTB time in patients presenting with STEMI. Currently, the most widely used strategy is to activate the cardiac catheterization laboratory (CCL) through a single page. Several studies report that this system significantly reduced the DTB time [6-19]. Based on this strategy, our institution implemented a 1-call “code heart I” protocol, CCL activation through a single page by Emergency physician .

ST-segment elevation myocardial infarction should be diagnosed quickly for prompt reperfusion. Accurate and quick reading of the electrocardiogram (ECG) is essential for proper diagnosis of STEMI. The ECG is the most immediately accessible and widely used diagnostic tool guiding emergency treatment strategies. However, physicians in charge of the primary medical examination in the ED may be inexperienced in reading ECGs. For this reason, it is thought that if the ECG is interpreted incorrectly, STEMI diagnosis can be delayed. In addition, if the ECG is ambiguous, it can be difficult to diagnose an STEMI. And a recent study reported on the poor accuracy

http://dx.doi.org/10.1016/j.ajem.2014.07.026

0735-6757/(C) 2014

Before code heart(N = 68) (between june 2010 and May 2011)

After code heart(N = 58)

(between June 2011 and May 2012)

Code heart I(N = 24) (between June to November 2011)

code heart II(N = 34) (between December 2011 to May 2012)

Patients whose diagnosis included the term ‘myocardial infarct’ in electronic medical record system

(N = 581)

The chart(ECG, Hx) was Reviewed by EP

Patients who were diagnosed with STEMI and received emergency CAG(N = 126)

Fig. 1. Flowchart showing the enrolment of study subjects. Code heart, the cardiac catherterization laboratory activation by single page (code heart I + code heart II); code heart I, the system to activate the cardiac catherterization laboratory by EP; code heart II, the system to activate the CCL by ECG machine auto-interpretation.

of experienced physicians for interpreting STEMI based on the ECG finding [20].

In an attempt to begin STEMI treatment more quickly (to reduce DTB time) by minimizing preventable delays in ECG interpretation./a>, CCL activation was changed from activation by the EP (code heart I) to activation by a single page if the ECG is interpreted as STEMI or ST elevation by the ECG machine (ECG machine auto-interpretation) (code heart II) in patients with symptoms of a suspected STEMI such as chest pain, dyspnea, syncope, and shortness of breath. Therefore, we investigated the effect of CCL activation by a single page and sought to compare its effect and appropriateness between EP initiating CCL activation (code heart I) and ECG machine auto-interpretation on CCL activation (code heart II).

  1. Methods
    1. Study design and patient enrolment

Our institution is a 1000-bed tertiary care university hospital located in Yangsan City, Korea. This study used a retrospective design and was approved by the institutional review board of our university. On June 1, 2011, our institution implemented a 1-call “code heart

I” protocol. As per the protocol, a single call from the EP to the central page operator triggered the simultaneous activation of the pagers of the on-call interventional cardiologist, catheterization laboratory personnel, and in-hospital cardiology fellow. If the attending EP (emergency resident or staff) suspected STEMI after reviewing the

Table 1

General characteristics of patients diagnosed with STEMI for each group, before CCL by single page

Type

Before code hearta

Code heart Ib

Code heart IIc

P

STEMI (n)

68 (54%)

24 (19%)

34 (27%)

DM (n)

19 (27.9%)

6 (25%)

9 (26.4%)

.959

HT (n)

26 (38.2%)

9 (37.5%)

18 (52.9%)

.322

Previous CAD (n)

8 (11.7%)

5 (20.8%)

2 (5.8%)

.223

Smoking (n)

35 (51.4%)

11 (45.8%)

16 (47%)

.814

Previous CABG or PCI

6 (8.8%)

3 (12.5%)

2 (5.8%)

.714

CK (U/L)

128.0 (93.0-400.0)

224.0 (114.0-579.0)

274.0 (141.0-617.0)

.518

CK-MB (ng/mL)

3.8 (2.0-17.1)

7.8 (1.7-67.9)

13.5 (3.7-73.1)

.711

Troponin I (ng/mL)

0.15 (0.02-2.73)

0.13 (0.04-12.66)

1.27 (0.05-13.60)

.998

Symptom duration (min)

120 (60-420)

240 (112.5-810.0)

480 (180.0-1600.0)

.350

Height (cm)

162.51 +- 9.12

164.38 +- 9.20

165.22 +- 7.04

.484

Weight (kg)

65.08 +- 11.60

64.33 +- 13.29

66.03 +- 17.38

.901

Age (y)

63.01 +- 11.55

62.38 +- 13.61

64.68 +- 13.58

.711

Male/female (n)

52/16

17/7

25/9

.699

Abbreviations: CAD, coronary artery disease; DM, diabetes mellitus; HT, hypertension.

a Cardiac catheterization laboratory activation by single page.

b Cardiac catheterization laboratory activation by EP.

c Cardiac catheterization laboratory activation by the ECG machine auto-interpretation.

Table 2

The effect of code hearta

Type Before code

heart

Code heart Ib/code heart IIc

Door-to-EKG

4.0 (3.0-7.2)

5.0 (3.0-7.0)

.611

time (min)

5.0 (3.0-7.0)/4.0 (2.5-7.5)

.173

DTB time (min)

67.5 (54.5-90.5)

62.0 (49.5-82.5)

.043

55.0 (44.0-81.5)/65.0 (54.5-87.6)

.177

After code heart P

aged 18 years or older who were diagnosed with STEMI at the time of discharge and who received emergency PCI (CAG and angioplasty) were evaluated for enrolment (Fig. 1). And the second objective is to compare appropriateness between code heart I and code heart II. To do this, patients who experienced the code heart system after its implementation were also included in this study (code heart I, between June and November 2011; code heart II, between December and May 2012; and code heart, code heart I + code heart II).

DTB time b90 min (n) 52 (76.4%) 56 (96.5%)

DTB time N 90 min (n) 16 (23.5%) 2 (3.5%)

.02

To enroll all patients who were diagnosed with STEMI, we selected all patients whose diagnosis included the term myocardial infarct or myocardiac infrarct in electronic medical record system. Among these

The number of door-to-EKG time and DTB time indicated the median and interquartile range.

a Cardiac catheterization laboratory activation by single page.

b Cardiac catheterization laboratory activation by EP.

c Cardiac catheterization laboratory activation by the ECG machine auto-interpretation.

patient’s history and interpreting the initial ECG, he was encouraged to activate the code heart system, code heart I.

After 6 months of using this system, it was changed. In an attempt to start STEMI treatment more quickly by minimizing delays in ECG interpretation (and reducing DTB time), the code heart system was changed to a system that activates CCL by a single page if the ECG is interpreted as an STEMI or ST elevation automatically by the ECG machine (ECG machine auto-interpretation); this was called code heart II. However, we limited this activation to only patients with symptoms suggesting an STEMI. The ECG machine used was a model produced by Philips (page writer Trim III electrocardiograph; Philips, Amsterdam, the Netherlands). When the code heart was activated in both systems (code heart I and II), the in-hospital cardiologist evaluated the patient within 10 minutes and, if necessary, performed a portable echocardiogram, whereas the interventional cardiologist and the catheterization laboratory team were expected to arrive within 30 minutes. Then, if the cardiologist did not diagnose STEMI, emergency Coronary angiography was canceled. Cardiac marker (creatine kinase [CK], CK-MB, and troponin I) level were measured in all patients.

The study period was from June 2010 to May 2012 (from June 2010 to May 2011, before code heart implementation; from June to November 2011, code heart I; and from December 2011 to May 2012, code heart II).

The first objective of this study is to investigate the effect of the code heart system implementation before, after code heart I, and after code heart II activation on the DTB time reduction. For this, all patients

Fig. 2. Difference of DTB times between before and after code heart?. ?Cardiac catheterization laboratory activation by single page.

patients, subjects who received emergency PCI were reextracted. The ECGs and initial clinical information for all extracted patients were independently reviewed by 2 EP who were blinded to the patient outcomes. Those patients were included in the study only when 2 reviewers agree that they are with STEMI. If there were any discrepancies, a third investigator arbitrated these issues (Fig. 1).

Time intervals were calculated separately by another 2 EPs, and any disagreement was settled by consensus.

The exclusion criteria were as follows: (i) prior use of fibrinolytic agents (tissue plasminogen activator), (ii) DTB time more than 90 minutes with a documented patient-related reason for delay such as initial refusal, cardiopulmonary resuscitation in the ED, etc, (iii) age younger than 18 years, (IV) transfer for coronary artery bypass graft (CABG), and (V) self-discharge.

Outcome measures and statistical analysis

To evaluate the effect of the code heart system (the first objective), we measured the DTB time and the percentage of DTB time less than 90 minutes before and after implementing the code heart system. And we compared DTB times and the percentage of DTB time less thanb 90 minutes between code heart I and II. In addition, to determine the appropriateness of the activation (the second objective), we com- pared percentage of STEMI and CAG performance rate between code heart I and II.

All analyses were performed using SPSS 18.0 software (SPSS Inc, Chicago, IL). Comparison of nonnormally distributed continuous variables among groups was assessed using the Kruskal-Wallis or Mann-Whitney tests. The ?2 or Fisher exact test was used to evaluate differences between categorical variables. A 2-tailed P b .05 was considered statistically significant.

  1. Results
    1. The effect of code heart implementation before, after code heart I, and code heart II activation on the DTB time reduction

During the 24-month study period, a total of 126 patients were diagnosed with STEMI and received emergency cardiac cath. Among the 126 patients, 68 were diagnosed with STEMI before implemen- tation of the code heart system. After its implementation, 58 patients were diagnosed with STEMI (code heart I, 24 patients; and code heart II, 34 patients (Fig. 1). The general characteristics were not significantly statistical difference among the 3 groups (Table 1).

Before implementation of the code heart system, the mean DTB time was 96.51 +- 65.60 minutes (median value, 67.5 minutes/ interquartile range (IQR), 54.5-90.5). After its implementation, the mean DTB time decreased to 65.40 +- 26.40 minutes (median value, 62.0 minutes/IQR, 49.5-82.5), a statistically significant reduction (P =

.043). There were 16 patients with DTB times more than 90 minutes before implementing the code heart system; however, after its implementation, the number of patients with DTB times more than 90 minutes decreased significantly to 2 (Table 2, Fig. 2).

To know the effect of code heart II, we compared the DTB time between code heart I and code heart II. The door to activation time

Fig. 3. Difference between code heart I and II. Cardiac catheterization laboratory activation by EP. Cardiac catheterization laboratory activation by the ECG machine auto- interpretation. ?P = .369, + P = .173, and ? P = .177.

(DTA) was 10.45 +- 8.71 and 8.37 +- 7.75 minutes (median value, 8.5 minutes/IQR, 4.0-14.0; 6.0 minutes/IQR, 4.0-10.5) in the code heart I and II groups, respectively (P = .369).The DTB time was 65.13 +- 36.30 minutes (median value, 55.0 minutes/IQR, 44.0-81.5) and 67.09 +-

16.54 minutes (median value, 65.0 minutes/IQR, 54.5-87.6) in the code heart I and II groups, respectively (P = .177) (Fig. 3). The percentage of DTB time more than 90 minutes was 4.1% (n = 1) and 2.9% (n = 1) in the code heart I and II groups, respectively, showing no statistically significant difference (P = 1.000).

The effect of the code heart implementation on the appropriateness activation of CCL

After implementing the code heart system, CCL activation occurred 204 times of which 38 were excluded (arrest, 4; CABG, 7; tissue plasminogen activator, 12; refusal of angiography, 12; and incom- pleted data, 3). We performed data analysis on 166 patients. In 32 cases, it was a code heart I; and in 134 cases, it was a code heart II. During the study period, there were no cases of STEMI in which the code heart system did not alert the CCL. Cardiac marker levels (CK, CK-MB, and troponin I) were lower in the code heart II group

Table 3

General characteristics of patients who experienced code hearta CCL activation by EP

than in the code heart I group. There were no statistically significant differences between the general characteristics of the groups (Table 3). ST-segment elevation myocardial infarction was diagnosed in 24 patients (75%) in the code heart I group and 34 patients (25.3%) in the code heart II group. Coronary angiography was performed in 28 patients (87.5%) in the code heart I group and 54 patients (40.2%) in the code heart II group (Table 4). The remaining patients did not receive CAG because the in-hospital cardiologist canceled the procedure based on his judgment (non-STEMI, variant angina, unspecific chest pain, et al). The STEMI diagnosis and the CAG performance rates were significantly lower in the code heart II group than in the code heart I group. Based on these results, CCL activation by ECG machine auto-interpretation did not reduce DTA or DTB time

and often unnecessarily activated the code heart system.

  1. Discussion

Prompt recognition of STEMI and treatment with early reperfusion therapy can have a significant effect on patient outcome [21-24]. In previous studies, the most important effect of shortening the DTB time is the reduced in-hospital mortality rate [1,2]. Therefore, several studies have been conducted to reduce DTB time. In November 2006, Bradley et al [25] identified 6 strategies that were associated with reduced DTB times. Subsequently, a single page activation of the CCL by the EP was proposed as a strategy to reduce the DTB time

[15,18,19,26,27,7,9,13]. Previous studies have shown that CCL

Type

Code heart Ia

Code heart IIb

P

Number

32 (19.3%)

134 (80.7%)

DM (n)

7 (21.8%)

34 (25.3%)

.822

HT (n)

10 (31.2%)

55 (41.0%)

.326

Previous CAD (n)

5 (15.6%)

24 (17.9%)

.120

Smoking (n)

16 (50.0%)

44 (33.3%)

.161

Previous CABG or PCI

4 (12.5%)

24 (17.9%)

.605

CK (U/L)

287.5 (103.2-587.2)

125.5 (79.5-276.5)

.011

CK-MB (ng/mL)

9.40 (3.20-9.45)

2.50 (1.30-9.45)

.003

Troponin T (ng/mL)

0.25 (0.03-4.07)

0.02 (0.01-0.23)

.001

Symptom duration (min)

195.0 (120-945)

300.0 (60.0-1440.0)

.838

Height (cm)

165.83 +- 6.87

164.69 +- 7394

.575

Weight (kg)

63.43 +- 12.7

62.98 +- 13.58

.885

Age (y)

60.70 +- 14.58

60.85 +- 16.53

.953

Male/female (n)

24/8

104/30

.429

activation by a single page improves DTB times [6,15,18,26,27], same as the result shown in our study. We experienced a significant reduction in DTB time and in cases of DTB time more than 90 minutes after implementation of the code heart system. Our research proved the efficiency of the single page activation as shown in previous studies.

However, the diagnosis of an STEMI is never easy in an emergency state. Electrocardiogram is the most immediately accessible and widely used diagnostic tool that guides emergency treatment strategies. In fact, an STEMI cannot be definitively diagnosed from an initial ECG, as the standard diagnostic criteria include a combination of clinical symptoms and serial ECGs and biomarkers. Unfortunately, this information is not known when the patient arrives in hospital. In addition, reading the ECG itself is not easy. Several

a Cardiac catheterization laboratory activation by EP.

b Cardiac catheterization laboratory activation by the ECG machine auto-interpretation.

studies show that even experienced cardiologists cannot accurately diagnose an STEMI with only an ECG [28,29]. However, physicians

Table 4

The appropriateness of CCL activationa

Type

Code heart Ia

Code heart IIb

P

Diagnosis (n) STEMI

24 (75.0%)

34 (25.3%)

b.001

Others

Intervention (n) PCI

8 (25.0%)

28 (87.5%)

100 (74.7%)

54 (40.2%)

b.001

NO

4 (12.5%)

80 (59.8%)

a Cardiac catheterization laboratory activation by EP.

b Cardiac catheterization laboratory activation by the ECG machine auto-interpretation.

who initially examine the patient and interpret the ECG in the ED usually have less experience compared with a cardiologist.

So, we expected the code heart II system to reduce DTB time by minimizing delays and preventing confusion in ECG interpretation. Although this system has the tendency to overtriage, overtriaging is an essential strategy in preventing the catastrophic consequences of undertriaging. Therefore, we also expected a decrease in the cases where DTB time is more than 90 minutes because of this tendency. Contrary to our expectation, we did not experience the reduction of DTA or DTB time on comparing code heart I and II, and there was no significant differences where DTB time was more than 90 minutes. Code heart II activated an unnecessary code heart too often compared with code heart I. Therefore, this system wasted money, time, and manpower, and as a result, the appropriateness and reliability of CCL activation by code heart I decreased.

Several studies have reported that CCL activation by an EP (EP initiating activation) was an effective strategy in reducing DTB time [7,12,13].The false-positive rate of single page activation of the CCL by the EP was also low and has been reported as approximately 10% of cases in several studies [9,30,31]. Our study showed that the STEMI diagnostic rate was 75% in code heart I. Comparing this with other studies, our false-positive rate was higher but was significantly lower than in code heart II cases (25%). In other words, code heart I has a significantly higher diagnostic rate of STEMI and lower false-positive than code heart II. Based on previous studies and our experience, EP initiating activation is the most effective strategy in reducing DTB time without unnecessary activation of the code heart system.

  1. Limitations

Our study has several limitations. First, it was a single-center study. Second, the retrospective nature of the study leaves it vulnerable to several biases. Our chart review was also limited by inaccurate or incomplete records. Third, the sample size is relatively small. Therefore, type I error cannot be excluded completely. Finally, not all of the patients who experienced the code heart system received emergency CAG. It is impossible to know the accurate diagnosis of these patients and the number of latent STEMIs that may have been missed.

  1. Conclusion

Cardiac catheterization laboratory activation by single page reduces significantly DTB time and in cases of DTB time more than 90 minutes. But CCL activation by ECG machine auto-interpretation does not reduce DTA or DTB times and often unnecessarily activates the code heart system compared with EP-initiated activation. This system therefore decreases the appropriateness of CCL activation.

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