Toxicity from which of the following medications may cause a patient to see a green-yellow halo around lights?

Choice A rationale:

Sinus tachycardia is a heart rhythm characterized by a rate greater than 100 beats per minute, with normal P waves preceding each QRS complex.

It can be caused by various factors, including exercise, stress, fever, dehydration, medications, and medical conditions such as anemia, hyperthyroidism, and heart failure.

In the given rhythm, the rate is within the normal range (60-100 beats per minute), and the P waves are not clearly visible, making sinus tachycardia unlikely.

Choice B rationale:

Atrial flutter is a type of supraventricular tachycardia characterized by a rapid, regular atrial rate of around 250-350 beats per minute, with a characteristic "sawtooth" pattern on the ECG.

It is typically caused by a re-entry circuit within the atria, often involving the cavo-tricuspid isthmus.

The ventricular rate is usually slower than the atrial rate due to the atrioventricular (AV) node's inability to conduct all atrial impulses.

Atrial flutter can cause symptoms such as palpitations, shortness of breath, lightheadedness, and fatigue.

It can also lead to complications such as stroke and heart failure.

The given rhythm shows a regular atrial rate with a sawtooth pattern, consistent with atrial flutter.

Choice C rationale:

Atrial fibrillation is another type of supraventricular tachycardia characterized by rapid, irregular atrial activity with no discernible P waves on the ECG.

It is also caused by disorganized electrical activity in the atria.

The ventricular rate in atrial fibrillation is also irregular, and the rhythm is often described as "irregularly irregular." The given rhythm shows a regular atrial rate, making atrial fibrillation unlikely.

Choice D rationale:

Normal sinus rhythm is the heart's natural rhythm, characterized by a rate of 60-100 beats per minute, with normal P waves preceding each QRS complex.

The given rhythm does not have normal P waves, making normal sinus rhythm unlikely.

Choice A rationale:

Increased afterload refers to the resistance against which the heart must pump to eject blood into the aorta. While increased afterload can contribute to chest pain in certain conditions like aortic stenosis, it's not the primary cause of angina.

Angina is typically triggered by exertion or emotional stress, which increase myocardial oxygen demand. Increased afterload doesn't directly cause this imbalance in oxygen supply and demand, making it less likely to be the primary driver of angina pain.

Choice B rationale:

Inadequate myocardial oxygenation is a key concept in understanding angina, but it's not the most precise answer to the patient's question about the cause of their pain.

It's important to explain the underlying reason for the inadequate oxygenation, which is coronary artery disease.

Choice C rationale:

Coronary artery disease (CAD) is the most common cause of angina. It's characterized by narrowing or blockage of the coronary arteries, which supply oxygen-rich blood to the heart muscle.

When the heart's demand for oxygen exceeds the supply available through the narrowed arteries, it experiences ischemia (lack of oxygen), leading to the characteristic chest pain of angina.

This explanation directly addresses the patient's question about the cause of their pain, linking the symptom to the underlying disease process. Choice D rationale:

Increased preload refers to the amount of blood filling the ventricles before they contract. While increased preload can contribute to heart failure and pulmonary edema, it's not typically a direct cause of angina.