The patient with restrictive cardiomyopathy asks the nurse what could have caused this disorder. Which response by the nurse is most accurate?

A. "The diaphragmatic nerve overdrives the rapid rhythm:" The phrenic (diaphragmatic) nerve controls the diaphragm for breathing and plays no role in cardiac rhythm regulation. It is unrelated to the autonomic control of heart rate or supraventricular tachycardia (SVT) management.

B. "Vagal stimulation decreases peripheral vascular resistance:" Vagal stimulation primarily affects the heart by decreasing the rate and conduction through the AV node. Its effect on vascular resistance is minimal, making this explanation inaccurate in the context of SVT treatment.

C. "The vagus nerve increases the heart rate, overdriving the rhythm:" The vagus nerve has a parasympathetic effect, slowing down the heart rate, not increasing it. Overdrive pacing is a different concept and not related to vagal maneuvers like carotid massage.

D. "The vagus nerve slows the heart rate": The carotid sinuses in the neck contain baroreceptors that are sensitive to pressure. Massaging these sinuses stimulates the vagus nerve to release acetylcholine, which in turn slows conduction through the AV node and may terminate episodes of SVT. This response demonstrates an accurate understanding of the purpose of the procedure.

A. The P-P and R-R distances are equal and regular: Equal and regular spacing between P-P and R-R intervals indicates that both atrial and ventricular rhythms are regular. This is a fundamental aspect of rhythm interpretation, helping to distinguish between regular and irregular rhythms such as atrial fibrillation or sinus arrhythmia.

B. The rhythm rate using a 3-second strip: Assessing the heart rate using a 3-second or 6-second ECG strip helps determine whether the rhythm is bradycardic, tachycardic, or within normal limits, which is crucial for accurate rhythm classification.

C. The duration of the U waves: U waves are typically small and follow the T wave. Although their presence can suggest conditions like hypokalemia, they are not routinely assessed in basic rhythm identification. Evaluating U wave duration is more relevant in electrolyte imbalance analysis than in identifying rhythm type.

D. There is a QRS complex after each P wave: A consistent QRS following every P wave indicates effective conduction from the atria to the ventricles. Each atrial depolarization (P wave) should be followed by a ventricular depolarization (QRS complex) if the signal is being conducted properly through the AV node. This finding supports a diagnosis of sinus rhythm and helps rule out AV blocks, where conduction may be delayed or blocked entirely.

E. P waves are present, upright and rounded: P waves that are upright and rounded in lead II suggest the electrical impulse is originating from the SA node. Their presence and morphology are essential criteria for identifying sinus rhythm and differentiating it from atrial arrhythmias like flutter or fibrillation.