A modifiable risk factor for coronary artery disease is:

Choice A rationale

Purkinje fibers are the terminal branches of the cardiac conduction system located within the ventricular walls. They rapidly conduct electrical impulses to the myocardial cells to trigger ventricular contraction. While they possess inherent automaticity and can act as a tertiary pacemaker if other nodes fail, their intrinsic rate is very slow, typically 20 to 40 beats per minute. They are not the primary pacemaker under normal physiological conditions but rather the final stage of impulse distribution.

Choice B rationale

The Bundle of His, or the atrioventricular bundle, receives electrical impulses from the AV node and transmits them toward the apex of the heart via the bundle branches. It serves as a critical bridge for electrical conduction between the atria and the ventricles. Although it has a secondary pacemaker ability with an inherent rate of 40 to 60 beats per minute, it only takes over if the SA node fails to function correctly or if conduction is blocked.

Choice C rationale

The sinoatrial node, located in the right atrium, is known as the natural pacemaker of the heart. It initiates the electrical impulses that set the rhythm and rate of the cardiac cycle. In a healthy adult, the SA node fires at an intrinsic rate of 60 to 100 times per minute. This impulse spreads through the atria, causing them to contract, and then travels to the rest of the conduction system to coordinate a synchronized heartbeat.

Choice D rationale

The atrioventricular node is situated at the junction between the atria and ventricles. Its primary role is to delay the electrical impulse briefly, allowing the atria to finish contracting and the ventricles to fill with blood before they contract. The AV node can act as a secondary pacemaker with a rate of 40 to 60 beats per minute if the SA node is nonfunctional. However, it is not the primary site where the heart's normal rhythm is generated.

Choice A rationale

This clinical finding occurs when blood backs up into the pulmonary circulation from the left ventricle. Increased hydrostatic pressure in the lung capillaries causes fluid to leak into the alveoli, leading to shortness of breath when lying flat. This reflects left-sided cardiac dysfunction rather than right-sided failure. Normal capillary wedge pressure ranges between 4 and 12 mmHg, but this increases significantly when the left side fails to pump effectively.

Choice B rationale

This condition involves fluid accumulation in the lungs due to the inability of the left atrium and ventricle to move blood forward into the systemic circulation. It results in crackles, tachypnea, and cough. Since the right side of the heart pumps blood into the lungs, its failure would actually decrease pulmonary flow, not cause congestion. This symptom is a hallmark of left-sided heart failure and elevated pulmonary artery occlusive pressures above 18 mmHg.

Choice C rationale

When the right ventricle fails, it cannot effectively pump blood into the pulmonary artery, causing a backup into the superior and inferior vena cava. This systemic venous congestion leads to increased pressure in the hepatic veins. The liver becomes engorged with blood, leading to enlargement and tenderness. Central venous pressure typically rises above the normal range of 2 to 8 mmHg, indicating volume overload in the systemic venous circuit and hepatic congestion.

Choice D rationale

Right-sided heart failure increases systemic venous hydrostatic pressure, which forces fluid out of the capillaries and into the interstitial spaces. Due to gravity, this fluid primarily accumulates in the lower extremities of ambulatory patients or the sacrum of bedridden patients. Normal interstitial fluid volume is maintained by a balance of pressures, but right ventricular dysfunction disrupts this, leading to visible swelling. This is a classic sign of systemic backup from the right heart.

Choice E rationale

Chronic systemic venous hypertension from right-sided failure leads to fluid leakage into the peritoneal cavity. This occurs because the high pressure in the portal system and systemic veins overrides the oncotic pressure provided by albumin. Normal portal venous pressure is 5 to 10 mmHg; elevations beyond this due to heart failure cause significant abdominal distension. This systemic accumulation of fluid is characteristic of the right ventricle's inability to handle the venous return from the body.