A nurse is caring for a male infant who has stools mixed with blood and mucus. The nurse should recognize that which of the following diagnoses is associated with these findings?

Rationale:

A. There is a P wave before every QRS complex is correct because in a normal sinus rhythm, the electrical impulse originates from the sinoatrial (SA) node, the heart’s natural pacemaker. This impulse causes atrial depolarization, represented by the P wave, followed by ventricular depolarization, represented by the QRS complex. The presence of a P wave before every QRS complex ensures that the atria are properly contracting and contributing to ventricular filling, which is critical for efficient cardiac output. This pattern is a hallmark of normal conduction and sinus rhythm.

B. The T wave is in the upside down position is incorrect because in a normal ECG, the T wave should be upright in most leads, including leads I, II, and V2–V6. Inverted T waves can indicate myocardial ischemia, infarction, electrolyte imbalances (e.g., hypokalemia), or ventricular strain, which are pathological changes, not normal findings.

C. The QRS is not present in every fourth beat is incorrect because missing QRS complexes indicate dropped beats, which could be due to heart blocks, premature atrial or ventricular contractions, or other conduction abnormalities. This is not part of a normal rhythm and requires immediate assessment, especially in symptomatic clients.

D. The P-R interval measures 0.22 seconds is incorrect because the normal P-R interval ranges from 0.12 to 0.20 seconds. A P-R interval of 0.22 seconds indicates first-degree atrioventricular (AV) block, which is an abnormal conduction pattern where the impulse from the atria to the ventricles is delayed. While often asymptomatic, it is not considered a normal ECG finding.

Rationale:

A. Decreased blood pressure in the arms with increased blood pressure in the legs is incorrect because coarctation of the aorta narrows the aortic arch near the ductus arteriosus, usually after the vessels that supply the head and arms. This results in higher pressure in the upper extremities compared with the lower extremities, not the reverse.

B. Increased blood pressure in the arms with decreased blood pressure in the legs is correct because the obstruction in the aorta causes restricted blood flow to the lower extremities, leading to weak or delayed femoral pulses and lower blood pressure in the legs. Conversely, the upper extremities receive normal or elevated blood flow, resulting in higher blood pressure. This is a hallmark finding in coarctation of the aorta.

C. Decreased blood pressure in both the arms and the legs is incorrect because blood flow to the upper extremities is typically preserved or even increased, not decreased. Low pressure in both the arms and legs would suggest generalized shock or severe heart failure, not isolated coarctation.

D. Increased blood pressure in both the arms and the legs is incorrect because the obstruction limits perfusion to the lower body. While upper extremity pressure may be elevated due to increased resistance, lower extremity pressure is reduced, not increased.