Know The Difference: Heart Attack vs Cardiac Arrest

Welcome to the second installment of "Know the Difference," a series which seeks to clear up common medical misnomers. This week, we're tackling a one of the most prominent naming errors on television (and by extension, the public). The scene is a hospital room, with the patient lying in the bed looking quite unhappy and ill. In walk our doctors, who bear an uncanny resemblance to team featured on House. They chat with the patient briefly, exchange some comical banter with each other, and then the patient takes a turn for the worse. The camera pans up to the cardiac monitor, which shows a complete asystole (flat line). Everyone springs dramatically into action, but one of the doctors commits a medical student faux paus. "She's having a heart attack!" he exclaims, sending a brief jolt of pain to the frontal lobes of the clinical staff watching at home.

So what happened? Basically the hotshot doctor was confusing two conditions, heart attack and cardiac arrest. And since they are treated very differently, it is kind of a big deal to get it right. So how do you tell one from the other?

A cardiac arrest (CA) occurs when the heart is no longer pumping blood. This is determined clinically by checking for a pulse. If it is absent, congratulations; you now have a genuine emergency on your hands. When the heart stops pumping blood, oxygen and nutrients cannot circulate through the body, and waste begins to build up. Without intervention, CA is fatal in a matter of minutes (predominantly due to the lack of oxygen)(1). CA is treated differently depending on the cause and EKG interpretation. For instance, the most common one seen on TV is asystole:

Asystole. Note no discernible waves. Courtesy of wikipedia.

This is also the most common rhythm seen in Out-of-Hospital arrests(2). Asystole has a number of causes, some reversible some not. Typically, this rhythm is seen after prolonged pulselessness, so the prognosis is grim. The treatment usually involves reversing the underlying condition (toxicity, tamponade, tension pneumo, etc). What it does not involve is electrical shocks. Asystole is not a shockable rhythm. So, while making for very good television, our team of doctors would not be doing any good with the defibrillator in the typical case. Ventricular fibrillation (V-fib or VF) on the other hand, is shockable, even though it may not look like an abnormal rhythm to the untrained eye.

V-fib. Only random waveforms. Also courtesy of wikipedia.

VF is a pulseless rhythm where the heart is contracting randomly, out of sync. 

A heart attack (MI) is also a serious condition, but does not lead to death per se. An MI occurs when blood flow to the heart is reduced, classically causing chest pain (angina) and dyspnea(2). The reduction of blood flow is usually due to a narrowing in one or more of the coronary arteries. Thus, the primary intervention is to open the arteries back up (PCI) or bypass blocked portions (CABG). The main difference between MI and CA is that cardiac arrest is a complication of an MI. If the blood flow is cut off for too long, heart muscle (myocardium) will die. This can lead to arrhythmias or heart failure, which may lead to death. The EKG of a person having a heart attack can vary substantially, but here are some examples of anterior MIs.

Summary

CA: No pulse, heart is not pumping blood. Rapidly fatal. Treatment (resuscitation) depends on the rhythm appearance.

MI: Reduced blood flow to the heart via the coronary arteries. Muscle death may impair normal function of the heart and lead to death.

So the next time you're watching House or Gray's Anatomy (or ER for the slightly older readers), keep an eye on that monitor and get ready to call those actors out on their mistakes!

Sources

1.CPR - adult. PubMed Health. 2011. http://www.ncbi.nlm.nih.gov/pubmedhealth/PMH0001083/. Accessed July 15, 2012.

2. Mader TJ, et al. Out-of-hospital cardiac arrest outcomes stratified by rhythm analysis. Resuscitation (2012), http://dx.doi.org/10.1016/j.resuscitation.2012.03.033.

3. Heart Attack. PubMed Health. 2011. http://www.ncbi.nlm.nih.gov/pubmedhealth/PMH0001246/. Accessed July 15, 2012.