Current guidelines state that patients with compatible symptoms and ST-segment elevation (STE) in ≥2 contiguous electrocardiographic leads should undergo immediate reperfusion therapy. Aggressive attempts at decreasing door-to-balloon times have led to more frequent activation of primary percutaneous coronary intervention (pPCI) protocols. However, it remains crucial to correctly differentiate STE myocardial infarction (STEMI) from nonischemic STE (NISTE). We assessed the ability of experienced interventional cardiologists in determining whether STE represents acute STEMI or NISTE. Seven readers studied electrocardiograms of consecutive patients showing STE. Patients with left bundle branch block or ventricular rhythms were excluded. Readers decided if, based on electrocardiographic results, they would have activated the pPCI protocol. If NISTE was chosen, readers selected from 12 possible explanations as to why STE was present. Of 84 patients, 40 (48%) had adjudicated STEMI. The percentage for which readers recommended pPCI varied (33% to 75%). Readers’ sensitivity and specificity ranged from 55% to 83% (average 71%) and 32% to 86% (average 63%), respectively. Positive and negative predictive values ranged from 52% to 79% (average 66%) and 67% to 79% (average 71%), respectively. Broad inconsistencies existed among readers as to the chosen reasons for NISTE classification. In conclusion, we found wide variations in experienced interventional cardiologists in differentiating STEMI with a need for pPCI from NISTE.
Current guidelines for acute ST-segment elevation myocardial infarction (STEMI) emphasize the need for shortening door-to-balloon times in patients presenting with symptoms suggestive of myocardial ischemia and STE and encourage making triage decisions based on prehospital 12-lead electrocardiographic (ECG) transmission. However, although this approach has been shown to shorten times to the catheterization laboratory, less is known about the accuracy of such an approach. In the absence of ECG signs of left ventricular hypertrophy (LVH) or left bundle branch block, guidelines define STE as new STE at the J point in ≥2 contiguous leads with cut-off points of ≥0.2 mV in men and ≥0.15 mV in women in leads V 2 and V 3 or ≥0.1 mV in other leads. However, nonischemic STE (NISTE) is found in >90% of healthy men. Up to 15% of patients presenting with chest pain have NISTE. In the present study we assessed the ability of interventional cardiologists to differentiate between STEMI and NISTE using only electrocardiograms of consecutive patients for whom the primary percutaneous coronary intervention (pPCI) protocol had been activated by emergency department physicians.
Methods
A database of a large urban medical center contained records of 240 consecutive patients for whom the pPCI protocol had been activated because of suspected acute STEMI from January 2008 through December 2008. Two readers (V.T. and H.D.H.) collected 84 electrocardiograms showing STE in ≥2 contiguous leads. Patients with left bundle branch block or ventricular rhythms including electronic ventricular pacing were excluded. We also excluded patients whose patterns of STE did not meet guideline-based criteria for acute STEMI.
To confirm that ECG STE represented true acute STEMI, we performed detailed chart reviews that included final diagnoses from the in-hospital physician’s progress and discharge notes and examined reports of in-hospital coronary angiograms and echocardiograms. We also independently confirmed that those cases diagnosed as acute STEMI demonstrated the typical increase and decrease in cardiac marker levels (e.g., cardiac troponin I and creatine kinase-MB) consistent with STEMI and that subsequent ECG tracings showed the typical evolution indicative of STEMI.
Seven experienced interventional cardiologists were then asked to analyze the electrocardiograms after all identifying information was removed and to decide whether they would send these patients for pPCI based on ECG findings alone, assuming patients had appropriate corresponding symptoms. Readers were blinded to clinical information for each patient including age, ethnicity, and gender; types of symptoms; and the clinical setting in which pPCI was activated. If readers did not think ECG findings warranted pPCI protocol activation, they were asked to code the electrocardiogram as NISTE and then choose from a list of 12 possible explanations as to why STE was present. Readers were allowed to code >1 reason to explain the cause of NISTE for each case. Readers were then assessed for overall accuracy, sensitivity, specificity, and positive and negative predictive values in correctly identifying patients with adjudicated STEMI.
Results
Forty patients (48%) had adjudicated true STEMI and 44 patients (52%) had NISTE (13 of these patients [30%] had positive cardiac markers suggestive of non-STEMI). Of the 84 patients (59 men, average age 61 years, range 25 to 90), 32 patients (38%) were white, 32 (38%) African-American, 12 (14%) Hispanic, and 9 (10%) of other ethnicities. Of the presenting symptoms, 62 patients (74%) had chest pain, 10 (12%) had shortness of breath, 5 (6%) had weakness, and 7 (8%) had other symptoms. With regard to risk factors, 57 patients (68%) had a previous diagnosis of hypertension, 46 patients (55%) had dyslipidemia, 30 patients (36%) had diabetes mellitus, and 27 patients (32%) had previously established coronary artery disease.
Percent electrocardiograms for which pPCI was recommended varied widely among readers (33% to 75%), with sensitivities ranging from 53% to 83% (mean 71%), specificities from 32% to 86% (mean 63%), positive predictive values from 52% to 79% (mean 66%), and negative predictive values from 67% to 79% (mean 71%; Figure 1 ) . Even when readers chose NISTE as the diagnosis, the cause varied ( Table 1 ). LVH, which is commonly found in our patient population, was thought to be the cause of NISTE by the individual readers in 6% to 31% of patients. Readers chose the option of old MI/aneurysm in 10% to 26% of cases. Interestingly, STEMI with spontaneous reperfusion as an indication not to activate the catheterization laboratory for possible pPCI was the least frequent choice (0% to 5%) in all patients with suspected NISTE.
| Reader | |||||||
|---|---|---|---|---|---|---|---|
| 1 | 2 | 3 | 4 | 5 | 6 | 7 | |
| Left ventricular hypertrophy | 21% (9) | 20% (4) | 31% (8) | 6% (3) | 14% (7) | 27% (9) | 10% (4) |
| Conduction defect | 17% (7) | 30% (6) | 4% (1) | 13% (7) | 12% (6) | 6% (2) | 3% (1) |
| Early repolarization | 19% (8) | 10% (2) | 4% (1) | 4% (2) | 18% (9) | 3% (1) | 8% (3) |
| Normal variant (mainly ST-segment elevation in leads V 1 –V 3 ) | 12% (5) | 10% (2) | 15% (4) | 2% (1) | 0% | 12% (4) | 13% (5) |
| No reciprocal changes | 0 | 0 | 0 | 27% (14) | 0 | 0 | 15% (6) |
| Concave ST-segment elevation | 0 | 10% (2) | 0 | 2% (1) | 20% (10) | 6% (2) | 8% (3) |
| Old myocardial infarction/aneurysm | 21% (9) | 10% (2) | 19% (5) | 13% (7) | 24% (12) | 12% (4) | 26% (10) |
| Spontaneous reperfusion | 0 | 5% (1) | 0 | 2% (1) | 0 | 3% (1) | 0 |
| Pericarditis | 10% (4) | 0 | 15% (4) | 4% (2) | 6% (3) | 18% (6) | 10% (4) |
| Brugada syndrome | 0 | 0 | 0 | 2% (1) | 2% (1) | 0 | 3% (1) |
| No ST-segment elevation | 0 | 5% (1) | 12% (3) | 25% (13) | 6% (3) | 12% (4) | 5% (2) |
| Other | 0 | 0 | 0 | 2% (1) | 10% (5) | 0 | 5% (2) |
| Total | 42 | 20 | 26 | 53 | 56 | 33 | 41 |
Results
Forty patients (48%) had adjudicated true STEMI and 44 patients (52%) had NISTE (13 of these patients [30%] had positive cardiac markers suggestive of non-STEMI). Of the 84 patients (59 men, average age 61 years, range 25 to 90), 32 patients (38%) were white, 32 (38%) African-American, 12 (14%) Hispanic, and 9 (10%) of other ethnicities. Of the presenting symptoms, 62 patients (74%) had chest pain, 10 (12%) had shortness of breath, 5 (6%) had weakness, and 7 (8%) had other symptoms. With regard to risk factors, 57 patients (68%) had a previous diagnosis of hypertension, 46 patients (55%) had dyslipidemia, 30 patients (36%) had diabetes mellitus, and 27 patients (32%) had previously established coronary artery disease.
Percent electrocardiograms for which pPCI was recommended varied widely among readers (33% to 75%), with sensitivities ranging from 53% to 83% (mean 71%), specificities from 32% to 86% (mean 63%), positive predictive values from 52% to 79% (mean 66%), and negative predictive values from 67% to 79% (mean 71%; Figure 1 ) . Even when readers chose NISTE as the diagnosis, the cause varied ( Table 1 ). LVH, which is commonly found in our patient population, was thought to be the cause of NISTE by the individual readers in 6% to 31% of patients. Readers chose the option of old MI/aneurysm in 10% to 26% of cases. Interestingly, STEMI with spontaneous reperfusion as an indication not to activate the catheterization laboratory for possible pPCI was the least frequent choice (0% to 5%) in all patients with suspected NISTE.
| Reader | |||||||
|---|---|---|---|---|---|---|---|
| 1 | 2 | 3 | 4 | 5 | 6 | 7 | |
| Left ventricular hypertrophy | 21% (9) | 20% (4) | 31% (8) | 6% (3) | 14% (7) | 27% (9) | 10% (4) |
| Conduction defect | 17% (7) | 30% (6) | 4% (1) | 13% (7) | 12% (6) | 6% (2) | 3% (1) |
| Early repolarization | 19% (8) | 10% (2) | 4% (1) | 4% (2) | 18% (9) | 3% (1) | 8% (3) |
| Normal variant (mainly ST-segment elevation in leads V 1 –V 3 ) | 12% (5) | 10% (2) | 15% (4) | 2% (1) | 0% | 12% (4) | 13% (5) |
| No reciprocal changes | 0 | 0 | 0 | 27% (14) | 0 | 0 | 15% (6) |
| Concave ST-segment elevation | 0 | 10% (2) | 0 | 2% (1) | 20% (10) | 6% (2) | 8% (3) |
| Old myocardial infarction/aneurysm | 21% (9) | 10% (2) | 19% (5) | 13% (7) | 24% (12) | 12% (4) | 26% (10) |
| Spontaneous reperfusion | 0 | 5% (1) | 0 | 2% (1) | 0 | 3% (1) | 0 |
| Pericarditis | 10% (4) | 0 | 15% (4) | 4% (2) | 6% (3) | 18% (6) | 10% (4) |
| Brugada syndrome | 0 | 0 | 0 | 2% (1) | 2% (1) | 0 | 3% (1) |
| No ST-segment elevation | 0 | 5% (1) | 12% (3) | 25% (13) | 6% (3) | 12% (4) | 5% (2) |
| Other | 0 | 0 | 0 | 2% (1) | 10% (5) | 0 | 5% (2) |
| Total | 42 | 20 | 26 | 53 | 56 | 33 | 41 |
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