Which of the following correctly lists the order of the electrical conduction system of the heart?
SA node - Bundle of His - Purkinje fibers - AV node.
SA node - AV node - Bundle of His - Purkinje fibers.
AV node - SA node - Bundle of His - Purkinje fibers.
Purkinje fibers - Bundle of His - AV node - SA node.
The Correct Answer is B
Choice A rationale
This sequence is incorrect because it places the Bundle of His before the AV node. The electrical impulse must pass through the AV node to allow for a physiological delay, which ensures the ventricles fill with blood from the atria before contracting. The Bundle of His receives the signal from the AV node. Moving from the Bundle of His back to the AV node would represent a retrograde or abnormal conduction pathway, which is not the standard physiological order.
Choice B rationale
The normal cardiac conduction starts at the SA node, the primary pacemaker located in the right atrium. The impulse travels to the AV node, where it is briefly delayed. It then moves to the Bundle of His, which splits into the right and left bundle branches. Finally, it reaches the Purkinje fibers, which distribute the electrical charge throughout the ventricular myocardium to trigger a coordinated contraction. This sequence ensures efficient blood flow from atria to ventricles.
Choice C rationale
This sequence incorrectly identifies the AV node as the starting point. While the AV node can act as a secondary pacemaker if the SA node fails, the standard physiological conduction system begins at the SA node. The SA node has the highest inherent firing rate, typically 60 to 100 beats per minute, which suppresses other potential pacemakers. Starting at the AV node would result in a junctional rhythm, which is a slower heart rate than a normal sinus rhythm.
Choice D rationale
This sequence represents the exact reverse of the normal conduction pathway. In a healthy heart, electricity does not move from the ventricles upward to the atria. Starting at the Purkinje fibers would mean the impulse originated in the ventricular tissue, which is characteristic of ventricular escape rhythms or premature ventricular contractions. Such a pathway would be highly inefficient and signifies a significant pathological state or a complete heart block where the primary pacemakers have failed.
Nursing Test Bank
Naxlex Comprehensive Predictor Exams
Related Questions
Correct Answer is A
Explanation
Choice A rationale
The post-ictal phase is the recovery period that occurs immediately after a seizure ends. During this time, the brain is recovering from the intense electrical activity of the tonic-clonic event. Patients commonly experience deep sleep, confusion, fatigue, and difficulty with arousal as neurotransmitter levels and metabolic functions return to baseline. This phase can last from minutes to hours and is a normal, expected component of the seizure cycle following the convulsive stage.
Choice B rationale
An aura is a focal neurological phenomenon that occurs before the onset of a seizure, often serving as a warning sign. It may manifest as sensory distortions, such as smelling something unusual or seeing flashes of light. Since an aura happens prior to the ictal or convulsive phase, it cannot describe the sleeping and unresponsive state that occurs one hour after the seizure has finished. Auras represent the beginning of abnormal electrical activity in a specific area.
Choice C rationale
An absence seizure, formerly known as petit mal, is a brief lapse in consciousness often characterized by staring into space or subtle eyelid fluttering. These seizures usually last only seconds and do not involve the violent tonic-clonic movements or a prolonged, difficult-to-arouse recovery period. The patient in this scenario had a tonic-clonic seizure, which is a generalized convulsion, making the classification of an absence seizure incorrect based on the severity and the described post-event state.
Choice D rationale
A behavioral disorder refers to a persistent pattern of disruptive or antisocial behavior that deviates from cultural norms. Difficulty arousing a patient following a major medical event like a tonic-clonic seizure is a physiological consequence of brain exhaustion and not a psychological or behavioral condition. Labeling this transient medical state as a behavioral disorder would be a clinical error, as it ignores the underlying neurological recovery process known as the post-ictal period.
Correct Answer is C
Explanation
Choice A rationale
Heart rate is the frequency of cardiac cycles measured in beats per minute. This parameter represents the chronotropic state of the heart rather than a volume-related measurement. Normal resting adult heart rate typically ranges from 60 to 100 beats per minute. Preload specifically concerns the end-diastolic volume, whereas Choice A describes a temporal measure of cardiac activity that contributes to total cardiac output but does not define the mechanical stretching of the ventricular fibers before contraction.
Choice B rationale
This description refers to afterload, which is the systemic vascular resistance the left ventricle must push against during systole. Afterload is determined by factors like aortic pressure and systemic vascular tone. While preload is a volume measurement occurring before contraction, afterload is the tension or stress developed in the wall of the left ventricle during ejection. Increased afterload can lead to decreased stroke volume if the heart cannot compensate for the increased resistance within the arterial system.
Choice C rationale
Preload is defined as the initial stretching of the cardiac myocytes prior to contraction. It is directly related to ventricular filling and the end-diastolic volume. According to the Frank-Starling law, as preload increases, the force of contraction increases to a point. Normal central venous pressure, which reflects right-sided preload, is 2 to 6 mmHg. Increasing blood return to the heart stretches the myocardial fibers, optimizing the overlap of actin and myosin filaments for an effective contraction.
Choice D rationale
This statement describes diastolic blood pressure, which is the minimum pressure remaining in the arteries when the heart is in a state of relaxation. Normal diastolic blood pressure for an adult is typically less than 80 mmHg. While this occurs during the same phase of the cardiac cycle as preload, it measures the pressure exerted on vessel walls rather than the volume or stretch within the cardiac chambers themselves. It is a component of systemic vascular resistance.
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