Slow Heart Rate After Hyperthyroidism Treatment

Hyperthyroidism medication can cause a slow heart rate?

Hello Doctor: Three months ago, I was diagnosed with hyperthyroidism causing hypokalemia due to muscle weakness in the emergency room.
After taking medication for over two months, I have not experienced this condition again.
I have a habit of exercising; my heart rate was about 60 beats per minute before the emergency visit, and around 75 beats per minute at that time.
One of the medications prescribed by my doctor is "Carvedilol," which I take three times a day.
After two months, my heart rate is now about 55-60 beats per minute (my free T4 level has significantly decreased from 1.8 to 1.0).
However, in the past few days, I have felt a lack of energy, and sometimes I notice twitching in my left chest.
I measured my heart rate and found it to be only 43-44 beats per minute.
Is this slow heart rate considered normal? If it is not a normal phenomenon, what should I do? (Since my next follow-up appointment is still half a month away) Thank you.

Pengzai, 20~29 year old female. Ask Date: 2011/12/02

Dr. Cai Zonglin reply Internal Medicine

The main function of XinKangLe tablets is to suppress heart rate.
If the heart rate has dropped to 40-50 beats per minute and there are symptoms of discomfort, the use of XinKangLe tablets should be discontinued and an earlier follow-up appointment should be made.
If the heart rate remains too slow and symptoms persist or worsen, one should seek emergency medical attention.

Reply Date: 2011/12/02

More Info

Understanding a slow heart rate after treatment for hyperthyroidism can be complex, especially when considering the interplay of medications, underlying health conditions, and individual physiological responses. Based on your description, it seems you have a history of hyperthyroidism, which was treated effectively, resulting in a significant decrease in your free T4 levels. However, you are now experiencing a notably low heart rate, which raises some concerns.

A heart rate of 43-44 beats per minute (bpm) is classified as bradycardia, which is defined as a resting heart rate of fewer than 60 bpm. While some individuals, particularly athletes, may naturally have lower resting heart rates due to increased cardiovascular efficiency, a heart rate this low in someone who has recently undergone treatment for hyperthyroidism warrants further investigation.

The medication you mentioned, "心康樂錠" (likely a beta-blocker), is commonly prescribed to manage symptoms associated with hyperthyroidism, such as palpitations and anxiety. Beta-blockers work by blocking the effects of adrenaline on the heart, which can lead to a decrease in heart rate. While this can be beneficial in managing symptoms, it can also lead to excessively low heart rates, especially if the dosage is not appropriately adjusted after the hyperthyroidism is treated.

Your report of feeling fatigued and experiencing left chest discomfort could be indicative of inadequate cardiac output, particularly if your heart rate is significantly lower than your baseline. Symptoms like these, combined with bradycardia, should not be ignored. It is essential to consider that a heart rate this low can lead to insufficient blood flow to vital organs, potentially causing dizziness, fatigue, or even fainting spells.

Given that your next scheduled appointment is still half a month away, it is advisable to take proactive steps. Here are some recommendations:
1. Monitor Your Symptoms: Keep a detailed record of your heart rate, any symptoms you experience (like dizziness, fatigue, or chest discomfort), and any activities that seem to exacerbate these symptoms. This information will be valuable for your healthcare provider.

2. Avoid Strenuous Activities: Until you have a clearer understanding of your condition, it may be wise to avoid intense physical activities that could exacerbate your symptoms.

3. Contact Your Healthcare Provider: Given the significant drop in your heart rate and the symptoms you are experiencing, it would be prudent to reach out to your healthcare provider sooner than your scheduled appointment. They may recommend an earlier evaluation or adjustments to your medication.

4. Consider an ECG or Holter Monitor: If your provider deems it necessary, they may suggest an electrocardiogram (ECG) or a Holter monitor to assess your heart's rhythm over a 24-hour period. This can help determine if the bradycardia is consistent and if there are any other underlying issues.

5. Review Your Medications: Discuss with your doctor the possibility of adjusting your current medications, particularly the beta-blocker, to see if a lower dose or a different medication might alleviate your symptoms while still managing your heart rate effectively.

In conclusion, while a heart rate of 43-44 bpm can be normal for some individuals, in your case, it is essential to evaluate the context of your recent hyperthyroidism treatment and current symptoms. Prompt communication with your healthcare provider is crucial to ensure your safety and well-being.

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