RVI

Safety and Effectiveness of Field Nitroglycerin in Patients with Suspected ST Elevation Myocardial Infarction

Mon, 12 Aug 2019 17:46:11 -0400 by Rogue Medic

Is prehospital use of NTG (NiTroGlycerin; GTN GlycerylTriNitrate in Commonwealth countries) safe for treating prehospital suspected STEMI (ST segment Elevation Myocardial Infarction) patients?

The evidence is limited, but does not suggest that prehospital NTG produces enough harm to discourage use in suspected STEMI. These researchers looked at the emergency department assessments of patients following prehospital NTG for suspected STEMI.

Despite the theoretical risk, the limited retrospective studies of NTG in the prehospital setting for multiple indications suggest that the medication is safe.^(10-13) However, with regard to NTG use for STEMI, the AHA International Consensus on Cardiopulmonary Resuscitation and Emergency Cardiovascular Care concluded that there was not enough evidence to determine the benefit or harm of out-of-hospital use of NTG.⁽¹⁴⁾ Given the high false positive rates for STEMI identified in the field, an additional concern is that many patients treated with NTG for presumed STEMI will ultimately have an alternate etiology for their pain.^{(15, 16)} Therefore, it is not clear that the benefits outweigh the risks of administering NTG to all patients with suspected STEMI in the field.^[1]

This paper helps to show the safety of prehospital NTG for suspected STEMI, providing evidence that blood pressure changes were similar in suspected STEMI patients with an SBP (Systolic Blood Pressure) of 100, or higher, regardless of whether they were treated with NTG. The study is a retrospective chart review, so we do not know why some of the patients were not treated with NTG.

One reason mentioned, but not discussed, is that only 22% (96 of 440) suspected STEMI patients not treated with NTG are documented to have had pain, but there is no information on the type of pain or other cardiac symptoms of the patients. Were the paramedics avoiding treating atypical chest pain, such as pressure, heaviness, gastric discomfort, difficulty breathing, et cetera? We do not know. Was only chest pain being documented, rather than shoulder, or arm, or jaw, pain? We do not know. Did the pain resolve prior to EMS arrival? We do not know. Were the paramedics correctly recognizing when the machine interpretation of the ECGs (ElectroCardioGrams) were wrong? We do not know.

The median Initial Pain Score is documented as 8, with an IQR (Inter-Quartile Range) of 5-9 for those treated with NTG. For those not treated with NTG the Initial Pain Score is documented as 0, with an IQR of 0-0. We do not know the Initial Pain Score of those who did have pain, but were not treated with NTG. All of these patients were in an IQR that was not documented in the paper. The good news is that the suspected STEMI patients not treated with NTG act as a control group, although possibly with important differences that are not discussed in the paper.

Click on the image of the LA County protocol to make it larger.^[2]

What about the 17% of suspected STEMI patients with SPB <100 mmHg who were treated with NTG?

Was medical command (California has certified MICNs [Mobile Intensive Care Nurses] providing medical command on the radio, with physicians available, as well) contacted for authorization to deviate from the protocol? If so, that is something that should be documented in the charts, which were reviewed for this paper. That information is not included in this paper. Those patients are much more interesting to me.

I do not object to using NTG to treat suspected STEMI with an SBP below 100 mmHg, but the authors seem to think that EMS should not even consider it. Do the outcomes of those patients support the approach of the authors? We do not know.

I suspect that the fears of bottoming out the blood pressure are very exaggerated, but it would be nice to have some evidence either way.

An important secondary end point was the differences between those with inferior/right ventricular STEMI, but treated with NTG.

By vasodilating all blood vessels, and the venous system in particular, it causes a drop in blood pressure and preload. Thus, there is concern for precipitating hypotension in ACS involving the right ventricle.^(1-3) Contraindications to the use of NTG, as outlined by the American Heart Association (AHA) Guidelines on the treatment of ACS, include right ventricular infarction.⁽⁴⁾ This raises concern for use in inferior ST-segment elevation myocardial infarction (STEMI) in the prehospital setting, since many inferior STEMI result from proximal right coronary artery (RCA) occlusion and 50% involve the right ventricle.⁽³⁾ Traditional 12-lead ECG is focused mainly on the left side of the heart and typically EMS protocols do not include acquisition of right-sided ECG leads. Further, in many systems, Basic Life Support (BLS) protocols allow for administration of NTG without differentiating the location of STEMI. There is also risk of other adverse events including bradycardia and cardiac arrest.^(5-9)^[1]

I have aggressively promoted the use of NTG for even hypotensive CHF/ADHF (Congestive Heart Failure/Acute Decompensated Heart Failure). Many physicians are not comfortable with that, even though the available evidence shows that aggressive IV NTG doubled the survival rate for these hypotensive patients. More research is needed on the use of NTG, especially in hypotensive patients.

Further, we did not find an increased risk of hypotension among patients with proximal or mid RCA occlusions confirmed on coronary angiography. There are several possible reasons for our findings. First, while right ventricular involvement in inferior STEMI is common, hemodynamic instability is actually rare due to the right ventricle’s more favorable oxygen supply-demand ratio compared to the left heart and more extensive collateral flow.^{(3, 22)} In addition, left heart occlusions may also involve the right ventricle and result in a preload dependent condition.^(23-25) While limited by sample size, our results suggests that specifically avoiding NTG use in inferior STEMI, which is common in EMS systems, may be misguided. One quarter of the local EMS agencies in the state of California, for example, currently prohibit the use of NTG in inferior STEMI.⁽²⁶⁾ This analysis would benefit from additional study with a larger sample size and specific information about the infarct territory. Further studies are needed to determine which patients, in particular, are at increased risk for hypotension when treated with NTG.^[1]

Perhaps NTG is also safe for treating patients with inferior ischemia and even right ventricular ischemia.

Footnotes:

^[1] Safety and Effectiveness of Field Nitroglycerin in Patients with Suspected ST Elevation Myocardial Infarction.

Bosson N, Isakson B, Morgan JA, Kaji AH, Uner A, Hurley K, Henry TD, Niemann JT.

Prehosp Emerg Care. 2018 Dec 17:1-9. doi: 10.1080/10903127.2018.1558318. [Epub ahead of print]

PMID: 30556765

^[2] Treatment Protocol: Chest Pain */ Acute MI

Reference No. 1244

LA County Paramedic Protocols

Los Angeles County Department of Health Services – Emergency Medical Services

Protocol

A Case of Very Rapid Cath Lab Activation.

Sun, 20 Apr 2008 22:36:00 -0400 by Rogue Medic

Last week Dr. Wes wrote The Race is On! about an article Saving a Life in 14 Minutes in the Boston Globe.

The article is interesting for a few reasons. It includes a time line, one that does not omit the EMS times. That is what I am going to focus on.

There are a few important questions from the time line.

8:31 EMS is dispatched.

8:34 EMS meets him at his front door. It should only take a couple of minutes to get to the ambulance and start transporting while assessing and treating. A 3 minute response time is good.

8:42 He is wheeled into the ambulance. 8 minutes later. It only took 3 minutes to “hop into an ambulance for the half-mile trip to Rosen’s house moments after his 911 call.“

8:50 The ambulance is en route and notifying the ED of a STEMI. Why not notify when the first 12 lead was done, if the goal is to reduce delays? Although in this case it does not seem to have mattered, not all hospitals will respond as quickly. Yet, another 8 minutes apparently on scene.

8:57 Arrival at the ED.

9:01 Wheeled through ED doors. It took 4 minutes to get from the ambulance to the ED doors? It took less time to drive to the residence and meet the patient at the front door.

Interesting that the only ED contact mentioned is on the radio. The 12 lead ECGs are handed to a cardiology fellow, who works in the cath lab. They go straight through the ED to the cath lab, without stopping. Is there any improvement to the care of the patient that might be contributed by stopping in the ED? No.

The rest of the time line is in the story, but does not relate to EMS as much.

In the ambulance bay, the paramedics perform a second EKG to hone in on the site of the attack. As Rosen’s pain intensifies, they insert IVs and give him morphine and fluids.

They are referring to the interior of the ambulance as the ambulance bay, not the area at the ED where ambulances park. A 2nd 12 lead is nice, but all of this can be done en route – including IVs and drugs. 12 leads can be done while moving. Shaving the chest, if necessary for application of leads, can be done with an electric razor while moving. Using benzoin makes a big difference in getting leads to stick, which can otherwise cause a lot of delays in obtaining a readable 12 lead.

The description of treatment suggests that this was an RVI (Right Ventricular Infarction), since no NTG (NiTroGlycerin in the US, or GTN – Glyceryl TriNitrate elsewhere) was given, but fluids were given (perhaps I am just reading too much into it). There is not much reason to sit on scene for this stuff. Things that do matter are access to the front door of the residence with the stretcher. Was this a reason for delay? Why morphine, when fentanyl is a safer drug – especially with RVI?

If “Kevin and I recognized his heart attack immediately,” why does it take so long to get going?

A study in The Journal of the American College of Cardiology looked at the best practices for improving door to balloon times.

The ideal process (Fig. 1) represents a synthesis of the best practices found in the sample of 11 hospitals and is not meant to reflect the specific process of any single hospital in the study. The door-to-balloon process for patients transported to the ED with a prehospital ECG performed and read by a paramedic before hospital arrival is depicted by Path #1 in Figure 1.

For patients with a pre-hospital ECG indicating STEMI, the benchmark door-toballoon time is 60 min (Fig. 2).

For patients arriving without a pre-hospital ECG, the benchmark door-toballoon time is 80 min (Fig. 3).

No need for telemetry to further delay patient treatment.

Looking at the times:

8:31 response, 8:34 patient contact at front door, 8:42 in ambulance, 8:50 en route with STEMI notification by radio, 8:57 at ED, 9:01 rolling through ED doors and by-passing the ED.

8 minutes from the patient’s door to the ambulance. He met EMS at the door.

8 minutes from entering the ambulance until en route (not sure if I am reading this correctly).

4 minutes from the ambulance arrival at the ED to the ED doors.

There are 20 minutes that could not be completely eliminated, but should be dramatically reduced.

The time from door to balloon is less than the amount of the apparently avoidable EMS delays.

I realize that this article may not be accurate, that these times can never be completely eliminated, that I am reading a bit into this article, but WTF?

Historically, almost all of the unnecessary delays have been in the hospital. Here, it is the hospital that seems to have its act together. Ideal timing does seem to be one thing working in the favor of this patient. He arrived at 9 AM on a week day. The cath lab may have been preparing to take their first scheduled, non-emergency patient of the day and just had to defer that case for a while.

The cardiology fellow is waiting in the ED for the patient. There is little reason for the ED to be involved in the care of this patient. Look at the amount of time saved by the EMS notification of a cath lab patient and by the cath lab staff coming to the ED to take the patient directly to the cath lab.

Let’s add in the 4 minutes that the ambulance was at the ED, but not yet through the doors – 18 minutes door to balloon.

Just to complicate things we can put some butter on the fingers of Dr. Shah, who took just 6 minutes from initiating femoral access to inflating the balloon. How about adding 30 minutes – adding 5 times as long as it actually took. This would still give a door to balloon time of 48 minutes. The AHA and JCAHO goal is less than 90 minutes. This is just a smidge more than half of that goal.

If we can by-pass the ED, difficult if the cath lab team is not in the hospital, the amount of time saved is tremendous. This is not a criticism of the ED – we do the same thing with trauma. The cath lab team needs to be prepared to take the patient right away.

Bradley EH, Roumanis SA, Radford MJ, Webster TR, McNamara RL, Mattera JA, Barton BA, Berg DN, Portnay EL, Moscovitz H, Parkosewich J, Holmboe ES, Blaney M, Krumholz HM.
Achieving door-to-balloon times that meet quality guidelines: how do successful hospitals do it?
J Am Coll Cardiol. 2005 Oct 4;46(7):1236-41.
PMID: 16198837 [PubMed – indexed for MEDLINE]