From the Guidelines
The patient's fluctuating heart rate between tachycardia and bradycardia, specifically ranging from 120 to 80 beats per minute, is most likely caused by a condition known as tachycardia-bradycardia ("tachy-brady") syndrome, as defined in the 2018 ACC/AHA/HRS guideline on the evaluation and management of patients with bradycardia and cardiac conduction delay 1.
Possible Causes
The tachycardia-bradycardia syndrome is characterized by alternating periods of abnormal atrial tachycardia, atrial flutter, or atrial fibrillation with periods of sinus bradycardia, ectopic atrial bradycardia, or sinus pause. This condition can be caused by various factors, including sinus node dysfunction, atrioventricular block, or conduction tissue disease.
Diagnostic Approach
To determine the underlying cause of the patient's fluctuating heart rate, a thorough evaluation, including a physical examination, medical history, and electrocardiogram (ECG) or Holter monitor, is necessary. The ECG or Holter monitor can help identify patterns of tachycardia and bradycardia, as well as other potential arrhythmias.
Treatment Options
Treatment for tachycardia-bradycardia syndrome depends on the underlying cause and may include lifestyle modifications, medications, or addressing underlying conditions such as thyroid disorders, anemia, or dehydration. Medications like beta-blockers (such as metoprolol 25-100mg daily) or calcium channel blockers (like diltiazem 120-360mg daily) may be prescribed to control heart rate and prevent symptoms.
Key Considerations
It is essential to distinguish the patient's condition from other potential causes of tachycardia, such as hyperthyroidism, anemia, dehydration, pain, or use of exogenous substances and drugs of abuse, as mentioned in the 2015 ACC/AHA/HRS guideline for the management of adult patients with supraventricular tachycardia 1. Additionally, the patient's symptoms and medical history should be carefully evaluated to determine the best course of treatment.
From the FDA Drug Label
Bradycardia, including sinus pause, heart block, and cardiac arrest have occurred with the use of metoprolol. Patients with first-degree atrioventricular block, sinus node dysfunction, or conduction disorders may be at increased risk. Monitor heart rate and rhythm in patients receiving metoprolol. If severe bradycardia develops, reduce or stop metoprolol
The cause of the patient's fluctuating heart rate between tachycardia and bradycardia may be related to the use of metoprolol, as it can cause bradycardia. However, the exact cause of the fluctuation between 120 to 80 beats per minute cannot be determined from the provided information.
- Key factors to consider:
- Metoprolol use
- Underlying heart conditions, such as first-degree atrioventricular block, sinus node dysfunction, or conduction disorders
- Monitoring of heart rate and rhythm is necessary when using metoprolol 2
From the Research
Possible Causes of Fluctuating Heart Rate
The patient's fluctuating heart rate between tachycardia and bradycardia, ranging from 120 to 80 beats per minute, may be attributed to various factors. Some possible causes include:
- Atrial fibrillation, which is a type of supraventricular tachycardia that can cause an irregular and rapid heart rate 3
- The use of certain medications, such as metoprolol or diltiazem, which are commonly used to control heart rate in patients with atrial fibrillation, but may have varying effects on heart rate control 3, 4
- Underlying medical conditions, such as heart failure with reduced ejection fraction, which can affect heart rate and increase the risk of mortality 4
- Other factors, such as hypertension, which can influence heart rate and mortality risk 5
Factors Influencing Heart Rate Control
Several factors can influence heart rate control in patients with atrial fibrillation, including:
- The type of atrial tachyarrhythmia, with paroxysmal and persistent atrial tachyarrhythmias requiring different doses of amiodarone for effective heart rate control 6
- The use of other medications, such as catecholamine infusion, which can affect heart rate control 6
- Electrolyte levels, such as magnesium, which can influence heart rate control when used in conjunction with amiodarone 6
- The presence of underlying medical conditions, such as heart failure with reduced ejection fraction, which can affect heart rate control and increase the risk of mortality 4
Mortality Risk Associated with Heart Rate
A heart rate greater than 80 beats per minute has been associated with an increased risk of mortality in patients with atrial fibrillation 7, 5. Additionally, a longitudinal study found that a mean resting heart rate of 80 beats per minute or higher was associated with an increased risk of mortality in patients with atrial fibrillation 7.