Medical Minute 5-18: Clot-Killing Drugs

By: Vanessa Welch Email
By: Vanessa Welch Email

Six years ago, architect John Cryer nearly died of a heart attack, but he was in the right city at the right time. On his way to the hospital, John got a clot-busting drug in the ambulance.

"The fact that I'm standing here today, I would contribute a lot to it."

Doctor James McCarthy at UT Health Science Center in Houston says that drug bought John precious time.

"Someone who calls 911 immediately and gets their artery opened up within the first 60 minutes, their likelihood of dying is very, very small," said James McCarthy, M.D. Emergency Medicine UT Health/Memorial Hermann.

The average person waits 90 minutes to call for help. Then it's another 90 minutes or more by the time doctors can open their arteries. Doctor Richard Smalling says their study shows giving the drug in the field saves lives.

"Eighty percent of the patients that get here after the first dose of drugs already have opened arteries. The heart attacks have been stopped not by the doctors, but by the paramedics," said Richard Smalling, M.D., Ph.D., Interventional Cardiologist UT Health/Memorial Hermann Hospital Houston, TX.

Results show patients who receive the drug have a 50% reduction in heart attack size. Bonnie Richter has seen the benefits firsthand.

Bonnie Richter Paramedic Houston Fire Department AT 1:01
"Your job as a paramedic, you want to get them to the hospital, hopefully, better than the condition you found them in, and this definitely gives you that opportunity."

Patients who get the drug are also 50% less likely to die.

"I mean you talk about saving one jumbo jet full of people every other day, that's a big difference in death from heart attacks."

John knows his outcome could have been much worse.

"Very lucky…very lucky."

For more information on other series produced by Ivanhoe Broadcast News contact John Cherry at (407) 691-1500,


WHAT ARE CLOT-BUSTING DRUGS? Clot-busting drugs, or thrombolytics, are drugs that are injected to break up or dissolve a blood clot in heart attack patients. Thrombolytics break up clots by forming an enzyme called plasmin that can break the bonds between the fibrin molecules that give a clot its structural integrity. (SOURCE:

Breaking up the blood clot unblocks the artery, which stops the heart attack and saves the heart from muscle damage. Use of a thrombolytic within 12 hours of a heart attack gives the patient a better chance of survival, but the sooner the clot-busting drugs are taken, the better. Thrombolytics work best for a heart attack if taken within three hours of the heart attack.

Clot-busting drugs are also useful for treating strokes. Many strokes are the result of a clot blocking the flow of blood to the brain. The clot-busting drugs can dissolve the clot and restore the flow of blood, limiting the damage and disability caused by the stroke. However, if the patient is having a hemorrhagic stroke, the clot-busting drug could increase the bleeding and worsen the stroke.

CAN YOU HAVE THROMBOLYTICS? Doctors take several factors into account when deciding whether or not to use clot-busting drugs to treat a heart attack or stroke. Some of them are:
• Age
• Gender
• Medical History: previous heart attacks, low blood pressure, diabetes, etc.

Doctors usually won’t give clot-busting drugs if:
• The patient has a recent head injury.
• The patient is pregnant.
• The patient has bleeding problems or bleeding ulcers.
• The patient is on blood-thinning medication.
• The patient has uncontrolled high blood pressure.


RISKS OF THROMBOLYTICS: The major risk of clot-busting drugs is hemorrhaging, which can possibly be life-threatening. About 25 percent of patients who have received thrombolytics will experience bleeding from their gums or nose, and very rarely (in about 1 percent of cases), patients who have received thrombolytics will bleed into the brain.

Deborah Mann Lake, Media Relations Specialist
University of Texas Health Science Center at Houston


Richard Smalling, M.D., Ph.D., an interventional cardiologist at UT Health/Memorial Hermann Hospital in Houston, talks about using a clot-busting drug in the ambulance to save patients who are having heart attacks.

What’s the biggest problem with the time it takes to get the patients, you know who are having a heart attack treatment to the emergency room?

Dr. Richard Smalling: Well there are two sources of time, one is when the patient has the symptom, chest pain, chest pressure, the elephant sitting on the chest, they sit and think about it a little bit. They don’t want to be having a heart attack so they deny it a little bit. Some people on the other hand, say “oh this is bad, call 911” so the best thing we can do is to have everybody call 911 when they have chest pain, not worry about being embarrassed, call 911; let them figure out if you’re having a heart attack or not, that’s the first step. The second step is once they call 911 or get to the hospital, it’s better to call 911 than to drive yourself to the hospital. The next step, is to perform an ECG. In many parts of the country the EMS system has ECG units on the ambulances so they go to the home or to the ballpark or wherever the patient is, and do the ECG, which is about 95% accurate in detecting if you’re having a heart attack. So if you’re having a heart attack they say “whoa, this is a heart attack we’ve got to get you to a hospital” where they can do an emergency catheterization, take pictures of the artery, find the blockage and reopen it to stop the heart damage.

I’ve read that the average time to get treated for a heart attack, by the time you get to the emergency room and get treated, is 90 minutes, is that accurate?

Dr. Richard Smalling: No, the average time is about 4 hours. And that’s way too long. The goal is to have an angioplasty done within 90 minutes of first medical contact but that’s still too long. We know now, from studies with magnetic resonance imaging, that if you don’t reopen that artery that’s blocked off with a blood clot within 2 hours, most of the heart muscle that could have been saved is dead, and so we really need to move that time earlier. One of the things we’ve done here in Houston is to initiate a pilot program that once the paramedic does the ECG which detects the heart attack, then we give half a dose of a clot busting medicine to try to reopen the artery. At the same time, we call all the team in that can take the patient to the cath lab to do the procedure to open the artery with a little balloon procedure if the medicine that we gave in the field doesn’t work. So by doing that, 80% of the patients that get here after the first dose of drugs already have opened arteries; the heart attacks have been stopped not by the doctors, but by the paramedics.

What is the clot busting medication?

Dr. Richard Smalling: There are currently 2 in use: We have used RetavaseTNK. TNK has also been used, for instance in a similar program in Minneapolis, and it’s probably not as important as to which you use but the idea is get the artery open as soon as possible.

And the drug works simply to thin the blood?

Dr. Richard Smalling: The drug is an enzyme that acts specifically on blood clots and it actively dissolves the blood clot. So what causes a heart attack? Well most of the serious heart attacks are caused by a buildup of cholesterol in the lining of the artery, one of the 3 arteries in the heart, which suddenly breaks open for a variety of reasons. The cholesterol, liquid cholesterol sort of squeezes into the artery like a toothpaste and that causes a blood clot to form almost immediately. Once the blood clot completely blocks the artery all the heart muscle supplied by the blocked artery starts to die. That’s a problem. You’ve got to reopen it in less than 2 hours otherwise you end up with a heart that pumps only 50% of what it usually should do.

The medication is typically given to heart attack patients sometime when they get to the hospital, right? The innovation here is that it’s being done in the ambulance.

Dr. Richard Smalling: Well there is a trend now, not to use medication at all, just do the angioplasty procedure, but unfortunately, in the U.S. it takes 4 hours from the time the patient has the symptoms to the time that balloons inflated to restore the blood flow. So we, heart attack specialists, have focused on getting the balloon procedure done quickly and have not focused on the actual time it takes to get the artery open by whatever means.

And why is that period so critical what is the difference between 2 hours and 4 hours or 90 minutes and 4 hours?

Dr. Richard Smalling: There have been several studies done in the last year that used magnetic resonance imaging to look at the amount of heart damage in heart attack patients. They correlated heart attack damage with the time from the onset of symptoms to the time an angioplasty had restored blood flow to the heart. These studies determined that in under 60 minutes, about 70 to 80% of the heart muscle can be saved that otherwise would have died and if you wait beyond 2 hours that number drops down closer to 20 to 30%. So there’s a big fall off in the benefit of treatment with prolonged time from the onset of symptoms.

And what does that mean for a patient who’s having a major heart attack to be able to restore blood flow so quickly?

Dr. Richard Smalling: We have shown by analyzing patients that have been treated at 4 other institutions around the world and ours, that if you can give a clot busting drug ahead of time and immediately do an angioplasty on patient arrival we can save about an hour of what we call the ischemic time, the time the artery is closed off. And that translates into a reduction in mortality rate from 6% or 6.7% at 30 days to 3%, a big difference without an increased risk of bleeding or stroke which are thought to be the major draw backs behind the clot busting drugs.

Well that’s what I was going to ask, why isn’t the clot busting drug used more often at least in a hospital or in an ambulance?

Dr. Richard Smalling: That’s a very good question and one we’ve been trying to address for a long time. There’s just a bias that the clot-busting drugs are dangerous, when in fact giving them at lower doses, with lower doses of blood thinners at the same time, the risks are no worse than the angioplasty procedure itself.

If somebody is already on Coumadin or something like that can they get this?

Dr. Richard Smalling: If somebody is on Coumadin, say they have atrial fibrillation or an artificial valve, it’s generally felt a little too dangerous to give the clot busting drug because the bleeding risk may be increased.

Ok so they wouldn’t be a candidate for this?

Dr. Richard Smalling: They generally wouldn't’t be. So you want to get them to the hospital real quick and get the angioplasty procedure.

Ok, is there anyone else who wouldn’t be a candidate?

Dr. Richard Smalling: Anybody who’s had a stroke, particularly in the last 6 months also would be at a little increased risk for having another bleed into the area where they had the stroke.

How do they know, is the EMT trained to ask those questions?

Dr. Richard Smalling: They are trained. All the people that participate with us and with other cities, it’s the same way. There’s checklist, just like an airplane pilot has before he or she takes off. You go through the checklist:“Have you had a stroke? –No. Is your blood pressure over 180/110? –No. Are you on blood thinners? –No.” Check go for drug.

So it minimizes any error?

Dr. Richard Smalling: Exactly

So you said it’s being done in other cities, but as a part of the pilot program correct?

Dr. Richard Smalling: It’s not adopted universally across the United States. We would love to do a trial randomizing people to either the half dose clot busting drug plus the angioplasty or what’s called primary angioplasty, to show the benefits, but unfortunately we have not been able to raise sufficient funds to fund the trial which would cost about $15 million.

And do you think, would that have to be the next step before this was adopted?

Dr. Richard Smalling: Yes, we think that a randomized trial would be the next step, so once you have irrefutable evidence that it’s safe and it saves 50% more lives than what is currently the Standard of Care, how can you argue with that?

Now when you say there are other places, is there just a handful of cities that are doing this or is it more widespread?

Dr. Richard Smalling: Well in terms of the number of cities in the U.S, it’s a handful, so a small percentage.

So it would still have to be randomized?

Dr. Richard Smalling: In the current cardiology experience, randomized trials really dictate what are called the guidelines of patient care.

So it’s a drug that’s already approved and used, but it seems like it has a big impact on patients, how big of a breakthrough is this?

Dr. Richard Smalling: I think it’s a big breakthrough and it’s something that would significantly impact public health care here in the United States. I mean, when you talk about saving one jumbo jet full of people every other day, that’s a big difference in death from heart attacks.

Do you have any other tips for people who think they are having a heart attack?

Dr. Richard Smalling: Well I think the most important thing is for them not to worry about whether or not people will make fun of them if they didn’t really have a heart attack and they cried wolf, it doesn’t matter, we’re in it to save lives. If they have chest pain and it just turns out to be the Mexican food they ate the night before, no problem, but if they have chest pain and it’s a heart attack, it needs to be taken care of and it needs to be done yesterday.

And is this being done as a study here? Do you have to get informed consent from someone who’s having a heart attack?

Dr. Richard Smalling: We stopped the study here because of a problem with some of the drug availability. We hope to restart it and involve more hospitals in the region, but once again, money is an issue. If we do the study, we have to fund the data collection and the analysis and we’re still working on finding funds to support the study.

So right now, you can’t count on getting pre hospital clot busting?

Dr. Richard Smalling: No, about a year ago we stopped; we’ll restart, hopefully, if we get some funding. The other thing is we have started giving the drug in transfer situations. We have 4 helicopters here that are stationed around the city so if a smaller hospital out in the community has a patient with a heart attack, then we can initiate the drug there. The helicopter goes and gets them, and 80% of the time by the time they get back here, the artery is already opened. If we don’t take that step the artery is closed for 4 hours or more typically.

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