A male client with a massive pulmonary embolus is tachycardic, hypotensive, and has audible bilateral pulmonary crackles. His arterial blood gas (ABG) results are: pH 7.0: PaCO, 66 mm Fig; HCO3- 24 mEq/L (24 mmol/L); PaO, 60 mm Hg. Based on these findings, this client is at greatest risk for which pathophysiological condition?

Reference Ranges:

pH [7.35 to 7.45] PaCO, [35 to 45 mm Hg]

HCO3- [21 to 28 mEq/L (21 to 28 mmol/L)]

PaO, [80 to 100 mm Hg]

A. Myocardial infarction:

Myocardial infarction (MI) typically presents with severe and prolonged chest pain or discomfort that is not relieved by rest or nitroglycerin. MI is characterized by myocardial necrosis due to prolonged ischemia, often resulting from the occlusion of a coronary artery by a thrombus or plaque rupture. While chest pressure and breathlessness are symptoms commonly associated with MI, the transient nature of the symptoms described by the client, as well as their relief after rest, is more indicative of stable angina rather than MI.

B. Unstable angina:

Unstable angina is characterized by new-onset angina, increasing frequency, or worsening intensity of angina symptoms. It is considered a medical emergency as it may precede a myocardial infarction. However, unstable angina typically presents with symptoms at rest or with minimal exertion and is not usually relieved by rest or nitroglycerin. The client's symptoms, which are relieved by rest, are more consistent with stable angina.

C. Stable angina:

Stable angina is characterized by predictable chest pain or discomfort that occurs with exertion or stress and is relieved by rest or nitroglycerin. The symptoms described by the client, including chest pressure and breathlessness that improve with rest, are consistent with stable angina. Stable angina occurs due to transient myocardial ischemia caused by an imbalance between myocardial oxygen supply and demand, often related to coronary artery disease.

D. Prinzmetal angina:

Prinzmetal angina, also known as variant angina, is characterized by chest pain or discomfort that occurs at rest, often in the early morning hours, and is typically caused by coronary artery spasm rather than fixed atherosclerotic lesions. While Prinzmetal angina can present with transient symptoms similar to those described by the client, it is less common than stable angina and is often associated with transient ST-segment elevation on electrocardiogram (ECG), which is not mentioned in the scenario.

A) An increase in afterload results in decreased systolic pressure, which creates a decreased cardiac output:

This statement is not consistent with the Frank-Starling law. Afterload refers to the resistance against which the heart must pump blood during systole. An increase in afterload typically results in increased systolic pressure, not decreased, as the heart works harder to overcome the increased resistance. However, increased afterload can lead to decreased cardiac output due to the increased work of the heart.

B) A decrease in afterload causes the cardiac muscles to hypertrophy, resulting in increased diastolic volume:

This statement is not consistent with the Frank-Starling law. Afterload refers to the pressure or resistance against which the heart must pump blood during systole. A decrease in afterload typically reduces the workload on the heart, which may lead to reverse remodeling and a reduction in cardiac hypertrophy. Increased diastolic volume may occur due to reduced afterload, but it's not the direct result of hypertrophy.

C) An increase in preload results in greater shortening of myocardial fibers, thereby increasing contractility:

Correct. According to the Frank-Starling law, an increase in preload (end-diastolic volume or stretch of myocardial fibers) leads to greater overlap of actin and myosin filaments within myocardial fibers during systole. This increased overlap results in stronger myocardial contraction (increased contractility), leading to an increased stroke volume and cardiac output.

D) A decrease in preload results in increasing diastolic muscle fiber length, which impedes contractility:

This statement is not consistent with the Frank-Starling law. Preload refers to the degree of stretch of the myocardial fibers at the end of diastole. A decrease in preload would lead to decreased stretch of the myocardial fibers, not increasing diastolic muscle fiber length. Decreased preload typically results in decreased contractility rather than impediment to contractility due to reduced myocardial stretch.