BY JIM DAVIS
Your medic unit responds to a 54-year-old male with chest pain. On your arrival, he appears pale and diaphoretic and states he was watching television when the pain developed. He denies shortness of breath. You place him on oxygen as your partner records his vital signs at B/P 118/64 R-18. You place the patient on a cardiac monitor and observe a normal sinus rhythm rate in the mid 60s and significant ST segment elevation in leads ll, lll, AVF. You establish an IV of 0.9 percent NS and give aspirin according to local protocol. You follow with 0.4 milligrams of sublingual nitroglycerin (NTG). After a second NTG spray, the patient develops hypotension with a systolic B/P of 64/P. You initiate a fluid bolus of 300 cc after ensuring his breathing sounds are bilaterally clear. The fluid does little for his blood pressure. You consider a second bolus while your partner prepares a dopamine drip. The patient’s blood pressure remains in the 60s, and the dopamine drip is initiated at five micrograms per kilogram per minute.
Despite aggressive treatment, you arrive at the emergency department with the patient still experiencing chest pain and his blood pressure still in the 60s. What causes this? Did the typical myocardial infarction (MI) treatment help or hurt this patient? What lessons did you learn for future runs?
REVIEW OF THE HEART
Firefighters easily understand heart function. The heart is a hollow, muscular organ. It acts as a pump, thereby maintaining blood circulation, much like a two-stage fire pump on your apparatus.
A two-stage fire pump operates on the principles of pressure and volume; the heart functions similarly. The right side of the heart must get blood flow to the lungs and back to the heart again; this is the principle of volume. As a result, the right ventricle is much thinner walled, requiring less oxygen than the left ventricle.1 The blood goes into the left side of the heart and must be pumped greater distances to get to the fingers and toes; this is the principle of pressure. The left ventricle has a much thicker wall than the right ventricle.
When a patient suffers an MI involving the inferior wall, EMS must consider several things. The inferior wall of the heart is served by the right coronary artery. ST segment elevation in leads II, III, AVF are diagnostic of this type of inferior infarction.2 Up to 90 percent of adults have a right coronary artery branch that supplies blood flow to the right ventricle. (2) If a patient has a thrombus in the right coronary artery, the resulting infarct may occlude this branch, which supplies blood flow to the right ventricle. This form of MI actually causes infarction of both ventricles.3 Studies indicate that 30 to 50 percent of inferior infarcts will involve the right ventricle during the course of their MI. (1) Approximately five percent of MIs are isolated to the right ventricle. Although isolated RV infarctions (RVI) are rare, these patients may have chest pains and have a normal 12-lead EKG.4An effective right ventricle requires both the ventricle and the inter-ventricular septum to be functioning correctly. When decreased perfusion occurs to this area, it causes the myocardium to become noncompliant and may decrease preload, significantly affecting cardiac output. This may lead to considerable hypotension (3) caused by the decrease in compliance, reduced filling capacity, and decrease in right side stroke volume. (1)
WHY IS THIS IMPORTANT?
RVIs become problematic for paramedics because the traditional treatment for chest pain and MI may actually cause these patients to develop hypotension and become unstable. A study published in the International Journal of Clinical Practice in April 2004 stated that RVI was associated with considerable morbidity and mortality and that in-hospital mortality was higher in patients with an RVI than those with an isolated inferior wall MI. (4)
Nitroglycerin and morphine sulfate (MS) are two common medications given for chest pain and MI. They provide pain relief and decrease myocardial oxygen demand to a stressed heart. These medications create vasodilatation of the vessels, allowing for more blood flow, oxygen, and peripheral pooling, reducing preload.5 In the patient with pulmonary edema, this is the needed effect. However, in a patient with an inferior MI having right ventricle involvement, NTG and MS begin a cascade effect, leading to further complications.6
Since the right ventricle has a much thinner wall than the left ventricle, it cannot tolerate the lack of blood flow. The strength of contractions actually decreases and compromises effective pump function. The traditional medications for MI and NTG and MS cause peripheral pooling and vessel vasodilatation. The preload reduction decreases the amount of fluid in the ventricles. Moving the fluid to the peripheral spaces creates insufficient volume for the ventricles to pump effectively. The effect of these medications creates a situation similar to “cavitation” of the fire pump.
When RVI patients develop hypotension, we routinely give small fluid boluses (of 200 to 300 milliliters) and then move to pressors. Most seasoned medics remember when MI patients were fluid restricted. IV therapy was typically D5W at a keep open rate. Today, most EMS protocols suggest dopamine for hypotension unresponsive to fluids. One of dopamine’s effects on blood pressure is that it increases cardiac output by increasing the heart rate. When no fluid is in the pump, you may constantly increase the rate and not see an increase in blood pressure. It is the equivalent of a pump operator’s increasing the pump pressure without cutting in a hydrant. Eventually, the tank dries up and the pump cavitates without a secure water supply. These patients will continue to be hypotensive.
HOW IS RVI DIAGNOSED IN THE FIELD?
A patient with an inferior wall MI must have a right-sided EKG done immediately after an MI diagnosis; move the left chest leads to the same positions on the right side chest wall. ST segment elevation of one mm or more in leads V4 right through V6 right (V4R-V6R) is a positive indication for a right ventricular infarct. (1)
While a complete right-sided EKG is preferred, some EMS situations make this impractical. In such instances, a quick way to look for RVI presence is to take the left leg of the four lead limb leads and move it to the V4 position on the right side of the chest and move the EKG machine to lead III. By doing this, the left leg becomes a positive camera that, when placed in the V4R position, looks directly at the right ventricle. (2) Even the slightest ST segment elevation (one mm or more) in this lead should raise suspicion of RVI presence (record this strip and mark it V4R). At this point, your patient has an inferior wall MI with RVI. The V4R lead is the best lead for determining RVI, with approximately 90 percent specificity. (2)
Other methods for RVI determination include pulsus paradoxus (the decrease or disappearance of the pulses during inspiration) and Kussmaul’s sign (abnormal deep and fast respirations). In a July 2000 article in Clinical Cardiology, Haji and Movahed report that hypotension patients with these signs show an 88 percent sensitivity and a 100 percent specificity for a clinically significant RVI. (1)
WHAT IS THE TREATMENT?
Some consider NTG and MS contraindicated in RVI. Not all patients with RVI develop hypotension.7 EMS protocols must include the suspicion, assessment, and treatment of RVI in the acute MI patient. While there are clear risks to preload reduction in RVI, the advantages of pain relief and reducing oxygen demand make withholding NTG and MS unnecessary unless hypotension is present. With a normotensive patient in pain, use NTG and MS cautiously. Administer fluids to offset preload reduction, and take frequent vital signs to catch hypotension early.
If hypotension is present, 0.9 NS is the desired treatment using two large-bore IVs, ensuring that the patient’s breath sounds are bilaterally clear, comfortably administer significant volumes of fluids. Patients with RVI are noted for their jugular venous distention (JVD) and clear breath sounds. (1) Frequently, they require one to two liters of fluid to increase blood pressure. (3) By adjusting the fluid’s flow rate, you may titrate amounts of NTG and MS to help manage your patient’s pain level.
This concept involves filling the weakened right ventricle with fluid until it overflows to the lungs, picks up oxygen, and returns to the left side of the heart for distribution to the rest of the body. If fluid loading does not provide the desired blood pressure increase, some practitioners suggest low dose dobutamine for the pump effect to strengthen contractions. Dobutamine helps strengthen contraction of both the right ventricle and the ventricular septum without the dramatic heart rate increase. (1)
When you reach the emergency department (ED) with a diagnostic 12 lead displaying a possible inferior wall MI, showing documentation of elevation in the V4R lead assists the ED in employing the proper course of action more quickly; revascularization of the right coronary artery will be administered, saving heart muscle. Save yourself from dealing with a hypotensive patient before the hospital.
Viewed as a two-way pump, the heart is an easy concept to grasp. Inferior wall MI involving the right ventricle is prone to hypotension, and a right side EKG is standard care in all patients with this condition. All patients with inferior wall MI with hypotension should raise suspicion of an RVI. Do not restrict fluids from these patients provided that their bilateral breath sounds show no evidence of rales. It may take considerable amounts of fluid to stay ahead of the game. Use traditional MI treatments with caution, as they may cause hypotension.
ENDNOTES
1. Haji, Showkat, Assad Movahed, “Right Ventricula Infarction Diagnosis and Treatment.” Clinical Cardiology. July 2000 23, 473-482.
2. Phalen, Tim. The 12 lead ECG: In Acute Myocardial Infarction. Mosby. 1996.
3. Horan, Leo G., Nancy C. Flowers. “Right Ventricular Infarction: Specific Requirements of Management.” American Family Physician. Vol. 60, October 15, 1999.
4. Kahn, Joel K., M. Bernstein, “Isolated Right Ventricular Myocardial Infarction.” Annals of Internal Medicine. Vol. 118 Issue 9 May 1, 1993.
5. Mistovich, Joseph, Randall Benner. Advanced Cardiac Life Support. Prentice-Hall. 1998.
6. Marini, John J., Arthur P. Wheeler, Critical Care Medicine. Williams and Wilkins. 1999.
7. Liu, Rex. “Right Ventricular Infarction.” eMedicine. June 29, 2006.
JIM DAVIS is a captain/paramedic and EMS supervisor with the Columbus (OH) Fire Department. He is a flight nurse for Medflight of Ohio, an adjunct faculty member at Columbus State Community College, and a member of the Ohio State Board of EMS.
