Physiological Effects and Management of ST-Segment Elevation Myocardial Infarction (STEMI)

QUESTION

Martha had just finished dinner with her husband, and they had just sat down to watch television. She is 72 years old and has had a history of angina. Shortly after they sat down, Martha said she had indigestion and went to take some antacid tablets. An hour later, she began to feel warm, restless, and anxious. Her husband noticed she was looking pale and said he would take her to a nearby walk-in clinic. By the time they arrived, Martha said her left arm and shoulder were sore. Suspecting Martha was having a heart attack, her husband turned the car around and rushed her to the hospital. Three hours after the onset of her symptoms, Martha was receiving oxygen, fibrinolytic therapy, and nitroglycerin in the emergency ward. Afterward, she was moved to the cardiac unit for STEMI (Learning Objectives 5 and 6).

1. An ECG of Martha’s heart demonstrated an elevated ST segment. What are the physiologic effects of myocardial ischemia that produce this finding? What variables affect the ECG tracing of a patient with ACS?
2. What are the benefits of administering fibrinolytic therapy, nitroglycerin, and oxygen in the early management of STEMI?
3. What is the inflammatory response in the postinfarction recovery period? Why will Martha’s heart function be compromised after her STEMI?

ANSWER

Physiological Effects and Management of ST-Segment Elevation Myocardial Infarction (STEMI)

Introduction

This essay focuses on Martha, a 72-year-old woman who experienced symptoms suggestive of a heart attack and was diagnosed with ST-segment elevation myocardial infarction (STEMI). We will discuss the physiological effects of myocardial ischemia that lead to ST-segment elevation on an electrocardiogram (ECG), the benefits of fibrinolytic therapy, nitroglycerin, and oxygen in the early management of STEMI, and the inflammatory response and compromised heart function following a STEMI.

Physiological Effects of Myocardial Ischemia and the ST-Segment Elevation

Myocardial ischemia refers to inadequate blood supply to the heart muscle, typically due to a partial or complete blockage of a coronary artery. This leads to a reduction in oxygen and nutrient delivery to the affected area. The physiological effects of myocardial ischemia that produce ST-segment elevation on an ECG include:

Depolarization and Repolarization Abnormalities: Ischemia alters the electrical activity of cardiac cells, resulting in an imbalance between depolarization and repolarization. This imbalance leads to changes in the ST segment on the ECG, reflecting abnormal repolarization of myocardial cells in the ischemic area.

Transmural Ischemia and Subendocardial Ischemia: ST-segment elevation is commonly associated with transmural ischemia, which affects the full thickness of the myocardium. However, subendocardial ischemia, affecting only the inner layer of the myocardium, can also present with ST-segment elevation in certain circumstances.

Variables that can affect the ECG tracing in a patient with acute coronary syndrome (ACS) include the location and extent of the ischemic area, the duration and severity of ischemia, and the presence of other concurrent cardiac conditions or medications.

Benefits of Fibrinolytic Therapy, Nitroglycerin, and Oxygen in Early Management of STEMI

Fibrinolytic Therapy: Fibrinolytic therapy, such as administering drugs like alteplase or tenecteplase, aims to dissolve the blood clot causing the coronary artery blockage. By restoring blood flow to the affected area, fibrinolytic therapy helps to salvage ischemic myocardium, reduce infarct size, and improve patient outcomes.

Nitroglycerin: Nitroglycerin is a vasodilator that helps relax and dilate coronary arteries, reducing the workload on the heart and improving blood supply to the ischemic area. It can alleviate chest pain (angina) associated with myocardial infarction, enhance collateral blood flow, and improve myocardial oxygenation.

Oxygen: Administering supplemental oxygen helps increase oxygen delivery to the myocardium and other organs. It aids in reducing myocardial oxygen demand, minimizing ischemic injury, and supporting overall tissue oxygenation.

Inflammatory Response and Compromised Heart Function Post-STEMI

Following a STEMI, there is an inflammatory response triggered by the myocardial injury. This response involves the activation of immune cells and the release of inflammatory mediators. The inflammatory process leads to remodeling of the infarcted area, with the formation of scar tissue.

Martha’s heart function will be compromised after her STEMI due to the loss of viable myocardium in the affected area. The scar tissue formed during the healing process lacks contractile function, leading to impaired cardiac performance. The compromised heart function may result in reduced cardiac output, impaired left ventricular systolic function, and potential complications such as heart failure or arrhythmias.

Conclusion

In summary, Martha’s case of STEMI demonstrates the physiological effects of myocardial ischemia, leading to ST-segment elevation on the ECG. Fibrinolytic therapy, nitroglycerin, and oxygen play crucial roles in the early management of STEMI by restoring blood flow, improving coronary artery dilation, and enhancing oxygen supply to the myocardium. The postinfarction recovery period involves an inflammatory response and scar tissue formation, contributing to compromised heart function. Timely intervention and comprehensive postinfarction care are essential to minimize damage, optimize recovery, and mitigate long-term complications associated with STEMI.