A 54-year-old Caucasian male comes to the emergency room with retrosternal chest pain of 30 minutes duration. The patient also complains of sweating and mild dyspnea. A single tablet of nitroglycerin is delivered sublingually, and the patient's pain decreases significantly. The patient has experienced several similar episodes of pain over the last 12 hours, all of which resolved spontaneously. Which of the following ultrastructural changes would most likely indicate irreversible myocardial cell injury in this patient?

Question

A 54-year-old Caucasian male comes to the emergency room with retrosternal chest pain of 30 minutes duration.  The patient also complains of sweating and mild dyspnea.  A single tablet of nitroglycerin is delivered sublingually, and the patient's pain decreases significantly.  The patient has experienced several similar episodes of pain over the last 12 hours, all of which resolved spontaneously.  Which of the following ultrastructural changes would most likely indicate irreversible myocardial cell injury in this patient?

Quizplus · Accepted Answer

The appearance of vacuoles and phospholipid-containing amorphous densities within mitochondria generally signifies irreversible injury, and implies a permanent inability to generate further ATP via oxidative phosphorylation. When the mitochondria are injured irreversibly, the cell cannot recover. Simple mitochondrial swelling may be associated with reversible cellular injury, however. (Choice A) Myofibril relaxation is an early sign of reversible injury in cardiac myocytes, which occurs within the first 30 minutes of severe ischemia. Myofibril relaxation corresponds with intracellular ATP depletion and lactate accumulation due to anaerobic glycolysis during this period. (Choice B) Disaggregation of polysomes denotes the dissociation of rRNA from mRNA in reversible ischemic/hypoxic injury. Depletion of intracellular ATP is thought to promote the dissolution of polysomes into monosomes as well as the detachment of ribosomes from the rough endoplasmic reticulum. Disaggregation of polysomes results in impaired protein synthesis. (Choice D) Disaggregation of granular and fibrillar elements of the nucleus is associated with reversible cell injury. Another common nuclear change associated with reversible cell injury is clumping of nuclear chromatin, perhaps secondary to a decrease in intracellular pH. (Choice E) Triglyceride droplet accumulation is characteristic of reversible cell injury, especially in hepatocytes, and also in striated muscle cells and renal cells. This fatty change may result from the decreased synthesis of intracellular proteins that occurs with cell injury. In the hepatocyte, decreased production of lipid acceptor proteins prevents the normal incorporation of triglycerides into lipoproteins. Since triglycerides cannot be rapidly exported from the cell in the form of lipoproteins, they accumulate intracellularly. (Choice F) Glycogen loss is another early and reversible cellular response to injury. As a result of lowered mitochondrial ATP production, ATP must be supplied to the cell via anaerobic glycolysis of glucose derived from the cell's glycogen stores. Myocardial glycogen stores may be completely depleted within 30 minutes of the onset of severe ischemia. Educational Objective: Mitochondrial vacuolization is typically a sign of irreversible cell injury, signifying that the involved mitochondria are permanently unable to generate ATP.

A 54-Year-Old Caucasian Male Comes to the Emergency Room with Retrosternal