Bigeminy and bradycardia are two different types of abnormal heart rhythms. Bigeminy refers to a pattern on an electrocardiogram (ECG) characterized by normal heartbeats alternating with premature ventricular contractions (PVCs). Bradycardia refers to a slower than normal heart rate, generally defined as a resting heart rate below 60 beats per minute. While these two arrhythmias can occur together in certain circumstances, bigeminy itself does not directly cause bradycardia. However, the underlying heart conditions that lead to bigeminy may also disrupt the heart’s natural pacemaking abilities and contribute to bradycardia.
What is Bigeminy?
Bigeminy describes a heart rhythm pattern containing both normal heartbeats and PVCs in a repeating sequence. The term “bigeminy” comes from Latin: “bi-” meaning two and “geminus” meaning twin. In bigeminy, after every normal sinus heartbeat, an early extra beat occurs. This results in a rhythm that goes:
- Normal beat
- PVC
- Normal beat
- PVC
And so on. On an ECG, bigeminy has a characteristic pattern. The normal and PVC beats alternate, causing the heart rate to seem rapid, even though half of the beats are actually premature.
PVCs originate from improper electrical signals in the ventricles rather than the sinus node, the heart’s natural pacemaker. The early signals disrupt the regular rhythm by stimulating premature ventricular beats. PVCs are very common and most people experience them occasionally. Frequent PVCs may be symptomatic of underlying heart disease.
In bigeminy, every other beat comes from an early PVC rather than the sinus node’s normal impulse. Bigeminy falls under a broader category of arrhythmias known as premature complex heart rhythms. Besides bigeminy, other types include trigeminy (alternating pattern of two normal beats followed by a PVC) and quadrigeminy (groups of three normal beats alternating with one PVC).
Causes
Various conditions can trigger bigeminy, including:
- Heart disease like coronary artery disease or cardiomyopathy
- High blood pressure (hypertension)
- Valvular heart disease
- Electrolyte imbalances
- Drugs and medications
- Caffeine, alcohol, smoking
- Increased vagal tone
- Heart block
- Acute illness or infection
- Stress and anxiety
Often, the cause is unknown. In otherwise healthy individuals, transient bigeminy may just represent increased automaticity of ventricular cells. This can generate PVCs in response to factors like stress, stimulants, or acute illness.
Structural heart disease is a more common cause in older adults with persistent or frequent bigeminy. Here, the distorted heart architecture increases automaticity and irritability of ventricular muscle cells, making them more prone to generating PVCs and disrupting normal rhythm.
Bigeminy in acute heart block reflects the ventricles trying to escape the effects of slow conduction from the AV node to generate more beats. The premature beats help maintain cardiac output despite delayed AV conduction. This bigeminy is seen as a compensatory mechanism in acute heart block.
Symptoms
Many people with occasional bigeminy have no symptoms at all. The abnormal rhythm may be detected incidentally on an ECG or during cardiac monitoring. However, some individuals may experience:
- Palpitations – sensation of rapid, fluttering, or pounding heartbeat
- Chest pain or tightness
- Shortness of breath
- Lightheadedness or dizziness
- Fatigue
Symptoms, when present, are primarily due to the forceful ventricular contractions of the PVCs. In healthy people, bigeminy alone is not dangerous and requires no specific treatment. But frequent, symptomatic bigeminy may warrant further evaluation for underlying cardiovascular disease.
What is Bradycardia?
Bradycardia refers to an abnormally slow heart rhythm. It is defined as a resting heart rate under 60 beats per minute, though it only causes symptoms below 50 bpm. Some key points about bradycardia:
- Bradycardia reduces oxygen delivery to the body’s tissues since less blood is pumped per minute at lower heart rates.
- The normal intrinsic heart rate is 60-100 bpm. Bradycardia represents rhythm slower than this.
- Bradycardia may be a normal phenomenon in trained athletes or during sleep.
- Pathological bradycardia is usually caused by heart block or sinus node dysfunction.
- Symptoms include fatigue, dizziness, fainting, shortness of breath.
- Severe bradycardia can be life-threatening if it causes very low blood pressure, decreased blood flow to the brain, or ventricular arrhythmias.
Causes
Some common causes of pathologic bradycardia include:
- Sick sinus syndrome: Dysfunction of the sinus node, the heart’s primary pacemaker.
- Heart block: Delayed or blocked conduction of electrical impulses through the AV node or ventricles.
- Ischemia: Reduced blood flow to the sinus and AV nodes.
- Medications: Beta-blockers, non-dihydropyridine calcium channel blockers, digoxin.
- Electrolyte imbalances: High potassium, low sodium, low calcium.
- Hypothyroidism: May slow down the heart rate.
- Increased intracranial pressure: Pressure on the vagus nerves may enhance parasympathetic tone and slow HR.
- Neurocardiogenic syncope: Excessive vagal stimulation upon orthostatic stress or vasovagal episodes.
In some cases, no cause can be identified. Bradycardia can also be a normal phenomenon in well-conditioned athletes.
Symptoms
Symptoms of bradycardia include:
- Fatigue
- Dizziness or lightheadedness
- Fainting or syncope
- Shortness of breath
- Chest pain
- Confusion or memory problems
Symptoms arise from decreased blood flow to the body’s organs and tissues. Not everyone with bradycardia becomes symptomatic, however. The heart usually has sufficient pumping reserve to maintain adequate cardiac output at slower heart rates. Symptoms develop only when heart rates drop below 50-60 bpm. Severely low heart rates can be life-threatening.
Can Bigeminy Cause Bradycardia?
Bigeminy itself does not directly cause or lead to bradycardia. However, there are some scenarios in which bigeminy and bradycardia occur together:
1. Underlying sinus node dysfunction
Sometimes the conditions causing sinus node dysfunction can also increase ventricular irritability and promote PVCs. Sick sinus syndrome, ischemia to the sinus node, or sodium channel blocking medications (like beta-blockers) could slow the baseline heart rate while also triggering intermittent bigeminy.
So the underlying problem causes both bradycardia (due to sinus node dysfunction) and bigeminy (due to increased PVCs). But the bigeminy doesn’t directly cause the slow heart rate.
2. Bigeminy alternating with complete heart block
In complete heart block, none of the sinus node impulses are conducted to the ventricles. This causes the ventricular rate to slow dramatically.
Bigeminy may develop as “escaped” beats – the ventricles depolarize on their own to escape the effects of the block. This generates an alternating rhythm of blocked beats and PVCs in a bigeminal pattern.
Again here, the bigeminy does not cause the bradycardia of heart block. Rather, they occur simultaneously due to conduction system disease. The bigeminy represents a compensatory mechanism to increase heart rate during prolonged pauses.
3. Bidirectional ventricular tachycardia
Bidirectional VT is a rare arrhythmia characterized by frequent alternation between rapid ventricular tachycardia and slow ventricular rhythms or even asystole.
During the tachycardia portions, abnormal electrical pathways within the ventricles drive rapid rates between 140-250 bpm. During slow phases, ventricular activity may halt completely or slow dramatically. Slow rhythms under 40 bpm may result.
The alternation between ventricular tachycardia and profound bradycardia gives a bidirectional pattern on ECG. Bidirectional VT is often seen in the context of digitalis toxicity.
Here again, bradycardia coexists with intermittent bigeminy in an alternating bidirectional pattern. But the periods of bigeminy do not directly elicit the bradycardia.
4. Cardiac arrest
In pulseless electrical activity cardiac arrest, the ECG may show a highly irregular rhythm with characteristics of both bradycardia and bigeminy:
- Extremely slow ventricular rate <40 bpm
- Alternating QRS morphology of normal and premature beats
- No effective cardiac output despite ongoing electrical activity
This mixed arrhythmia reflects severe underlying cardiovascular collapse rather than bigeminy driving bradycardia in itself.
Diagnosis
Doctors use several approaches to diagnose bigeminy and bradycardia:
Medical History
Key topics in the medical history include:
- Presence of palpitations, dizziness, fainting, or shortness of breath
- Situations that trigger or relieve symptoms
- Duration of symptoms
- History of heart disease, arrhythmias
- Medications
- Caffeine, tobacco, alcohol use
- Family history
Physical Exam
The cardiovascular exam helps identify signs of structural heart disease and feel for irregular heart rhythms. Key components include:
- Blood pressure measurement
- Careful pulse assessment
- Listening to heart sounds
- Examining veins and extremities for signs of heart failure
Electrocardiogram (ECG)
The ECG provides key information by tracing the heart’s electrical activity. Findings in bigeminy and bradycardia include:
Bigeminy
- Alternating normal QRS complexes and PVCs
- Normal QRS followed by premature PVC
- Normal heart rate around 60-100 bpm
- Possible underlying ST segment changes, Q waves
Bradycardia
- Heart rate slower than 60 bpm
- P waves dissociated from QRS complexes in complete heart block
- Normal P waves with intermittent dropped QRS complexes in sinus block or arrest
- Slow junctional or ventricular escape rhythms
Ambulatory Monitoring
Holter monitoring or event recorders capture the ECG over an extended period of time. This helps identify intermittent arrhythmias, correlate symptoms with arrhythmia episodes, and assess response to treatments.
Electrophysiology Study
Electrophysiology studies involve catheters inserted into the heart to map electrical signaling and conduction pathways. They help identify arrhythmia triggers and sources.
Treatment
The appropriate treatment depends on the specific underlying cause for bigeminy and bradycardia in each case. Some general treatment approaches include:
Treating reversible causes:
- Discontinuing offending medications
- Correcting electrolyte imbalances like low potassium or magnesium
- Treating acute illnesses
- Managing heart failure
- Regulating thyroid hormone abnormalities
Pacemaker:
- Permanent pacemaker implantation may be used for symptomatic bradycardia from sick sinus syndrome, heart block, or sinus pause
- Pacemakers can eliminate long pauses associated with bidirectional VT
Medications:
- Reducing or stopping medications that promote bradycardia
- Anti-arrhythmic medications to suppress PVCs
- Anticoagulation if atrial fibrillation coexists
Radiofrequency catheter ablation:
- Eliminating arrhythmia triggers in the myocardium through targeted ablation
- Useful for reducing bigeminy or VT associated with bidirectional VT
In emergency cases of hemodynamic instability, urgent transcutaneous pacing, cardioversion, or IV medications may be required.
Many cases of asymptomatic bigeminy or minor bradycardia (over 50 bpm) do not require active treatment other than monitoring. But symptomatic, severe or progressive bradycardia warrants treatment to avoid complications.
Complications
Potential complications of bigeminy and bradycardia include:
Bigeminy
- Rarely leads to complications by itself
- May trigger more sustained ventricular tachycardia
- Indicates increased risk for future atrial fibrillation or more serious ventricular arrhythmias
Bradycardia
- Lightheadedness, syncope, and falls
- Heart failure
- Angina and myocardial infarction
- Seizures
- Cardiac arrest or sudden death if extremely low rates
Severe bradycardia is more likely to produce adverse effects due to low cardiac output. But symptoms and complications also depend on the underlying cause and individual comorbidities.
Prognosis
The prognosis for bigeminy depends largely on the underlying condition causing PVCs. In healthy individuals, benign bigeminy has an excellent outcome. But bigeminy signals increased risk in those with heart disease. Close monitoring for ventricular tachycardia, atrial fibrillation and more serious arrhythmias is recommended.
With bradycardia, the prognosis relates closely to the underlying cause:
- Temporary bradycardia from medications or electrolytes often resolves once the trigger resolves.
- Persistent bradycardia from irreversible sick sinus syndrome has a poorer outlook, especially if syncope occurs.
- Severe bradycardia can lead to life-threatening complications if not treated.
- With treatment via pacemaker or medications, many patients do well.
Bidirectional VT carries the highest risk of all causes, with 1-year mortality over 60% even with contemporary treatment.
Overall, the prognosis depends most on the underlying cardiac status and risks. Isolated benign bigeminy or mild asymptomatic bradycardia generally have good outcomes.
Conclusion
In summary:
- Bigeminy refers to PVCs alternating with normal beats, while bradycardia is a slow heart rate under 60 bpm.
- Bigeminy itself does not directly cause or lead to bradycardia.
- However, underlying medical conditions can trigger both bigeminy and bradycardia together.
- Bidirectional VT features rapid tachycardia alternating with severe bradycardia.
- Diagnosis involves ECG monitoring and clinical evaluation.
- Treatments aim to manage the underlying cause, along with medications or devices if needed.
- Prognosis depends primarily on the individual’s cardiovascular status.
- Benign forms have good outcomes, while severe, sustained, or symptomatic arrhythmias warrant close monitoring for complications.
In patients with concurrent bigeminy and bradycardia, treating the underlying medical conditions can often alleviate both arrhythmias. The bigeminy itself does not directly cause the slow heart rate, but rather stems from common cardiovascular pathologies affecting normal electrical conduction. With a proper diagnosis and management plan targeting the specific mechanism, many patients achieve good control of symptoms and favorable outcomes. However, bidirectional VT and symptomatic, sustained bradycardia warrant urgent evaluation and treatment to prevent significant complications. Overall, while bigeminy and bradycardia may coexist, there is no direct causative relationship. Their presence signals underlying cardiovascular disease requiring further analysis. With appropriate care, even complex arrhythmias like bidirectional VT can often be effectively managed.