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Sinus Bradycardia

When the resting heart rate is 60 beats per minute or less, it is defined as sinus bradycardia.


Presentation

In many individuals sinus bradycardia is asymptomatic. However, a few individuals will present with the following symptoms:

When obtaining a history in a patient with sinus bradycardia, one should obtain the following information to decipher the cause:

  • Prior history of myocardial infarction
  • Previous medical illness
  • Any toxic exposure to chemicals
  • Use of medications (eg beta blockers or calcium channel blockers)
Myxedema
  • Sinus bradycardia may also be related to metabolic abnormalities, including hypothermia (low body temperature) and myxedema.[mission4health.com]
  • Sinus bradycardia may also be related to metabolic abnormalities, including hypothermia and myxedema.[sjo.org]
Camping
  • The mutation associated with bradycardia is located near the cAMP-binding site; functional analysis found that mutant channels respond normally to cAMP but are activated at more negative voltages than are wild-type channels.[ncbi.nlm.nih.gov]
  • […] results in a constitutive shift of the dynamic auto-inhibitory equilibrium toward inactive states of HCN4 and broadens the free-energy well of the apo-form, enhancing the millisecond to microsecond dynamics of the holo-form at sites critical for gating cAMP[ncbi.nlm.nih.gov]
Sudden Infant Death Syndrome
  • OBJECTIVE: Recent evidence in literature shows that the long QT syndrome accounts for a fraction of the sudden infant death syndrome.[ncbi.nlm.nih.gov]
Respiratory Insufficiency
  • Besides a partial respiratory insufficiency, the patient was also presented with sinus bradycardia. Medical literature describes several cases of thyreotoxicosis in combination with bradycardia.[ncbi.nlm.nih.gov]
Heart Disease
  • To two probands of congenital LQT, 8 patients of structural heart disease treated by open heart surgery, 13 patients of structural heart disease without open-heart surgery, and 10 patients of normal controls, 24 hour-Holter monitoring was performed from[ncbi.nlm.nih.gov]
  • Ischemic heart disease was excluded by the results of radionuclide study and an exercise stress test.[ncbi.nlm.nih.gov]
  • Abstract The patient was a 55-year-old male with no history of heart diseases. He was administered recombinant IFN alpha-2b under the diagnosis of chronic hepatitis C.[ncbi.nlm.nih.gov]
  • Congenital heart disease could also be excluded.[ncbi.nlm.nih.gov]
  • Arrhythmias are rarely the initial presentation of structural heart disease in children. Most children with structural heart disease will present with signs of heart failure or cyanosis.[pedemmorsels.com]
Slow Pulse
  • Trained athletes are prone to bradycardia (slow pulses) with heart rates below 40 beats per minute common at rest.[rjmatthewsmd.com]
  • Symptoms of SSS include: fainting or fainting sensations fatigue dizziness palpitations (abnormal heart beats) very slow pulse (bradycardia) difficulty breathing chest pain mental confusion memory problems disrupted sleep It’s important to see your doctor[healthline.com]
Distractibility
  • Manipulation of the mandible during TMJ surgery has been observed in several cases to be directly associated with the development of sinus bradycardia as the joint is distracted during arthrotomy and arthroplasty procedures.[ncbi.nlm.nih.gov]
Convulsions
  • Abstract Sixteen infants, ages 6 weeks to 23 months, were evaluated because of syncopal attacks (n 6), apneic episodes (n 3), or a combination of syncope, apnea, or "convulsions" (n 7).[ncbi.nlm.nih.gov]

Workup

Physical exam

The physical exam in a patient with sinus bradycardia is often unremarkable. Palpation of the peripheral pulses may indicate a slow but regular heart rate. Other features on a physical exam may include the following:

  • Some patients may appear lethargic and drowsy. They may have difficulty getting up from a rested position.
  • There may be bluish discoloration of skin and lips due to decreased perfusion (cyanosis).
  • Peripheral edema may be present bilaterally, especially in the lower extremities.
  • Auscultation may reveal crackles and rales.
  • Mild to moderate dyspnea may be present at rest or from even the slightest exertion.

Laboratory studies

There is no specific laboratory study that has any definitive value in making the diagnosis of sinus bradycardia. The important thing is to order tests to exclude reversible causes of the disorder. When sinus bradycardia is suspected, levels of drugs like digoxin, lithium and electrolytes should be obtained. Other studies that may help depend on the clinical presentation and may include the following:

  • Blood glucose levels
  • Thyroid function tests
  • Toxicological screen

Imaging 

Without any specific indication, the role of X-rays is limited in evaluating a patient with sinus bradycardia.

Electrocardiography

The diagnosis of sinus bradycardia is confirmed with a 12-lead ECG. The ECG will reveal a regular heart rate, with upright P waves and a QRS complex of less than 0.12 seconds.

Holter monitor

In individuals in whom the disorder is intermittent, the use of a holter monitor may help identify sinus bradycardia. The holter monitor is usually worn for 24 hours and records the electrical activity of the heart.

Event recorder

In the last decade, miniature devices have been developed which can be surgically inserted under local anesthesia. These devices can monitor electrical activity of the heart from a few weeks to few months. Once the diagnosis is made, these tiny devices can be removed under local anesthesia without any adverse effects.

Exercise stress test

In some patients an exercise stress test may be done to ensure that the heart rate does increase while walking on a treadmill or riding a stationary bike. The test can determine if the heart rate increase is appropriate to the physical activity.

Short QT Interval
  • Abstract We describe the case of an asymptomatic girl with sinus bradycardia and short QT interval at birth, junctional bradycardia in infancy requiring single-chamber pacemaker, atrial fibrillation in adolescence, and V141M mutation in the KCNQ1 gene[ncbi.nlm.nih.gov]
Prominent U Wave
  • Note the prominent U waves in the precordial leads, a common finding in sinus bradycardia.[lifeinthefastlane.com]

Treatment

Emergency treatment

In many cases the patient has no symptoms and the finding of sinus bradycardia is made on a physical exam or an incidental ECG. If a patient with known sinus bradycardia is symptomatic and presents to the ED, then IV access should be obtained and the patient should be provided with oxygen. The patient should then be monitored. If the sinus bradycardia persist and is symptomatic, atropine may need to be administered intravenously. If the symptoms and bradycardia persists, transcutaneous pacing may be required in the ED [7].

Inpatient treatment

Once the patient’s condition has stabilized, the cause of bradycardia should be investigated. All unstable patients should be closely monitored and some may even require endotracheal intubation and transvenous pacing. These patients are best managed in the ICU [8][9].

When a patient is hemodynamically stable, the cause of sinus bradycardia can be worked up. Never send a symptomatic patient with sinus bradycardia for any tests like imaging without monitoring. A healthcare worker should accompany the patient in such scenarios.
The current guidelines state that in adult patients who have persistent sinus bradycardia with symptoms, cardiac pacing is recommended. In individuals with sinus bradycardia but no symptoms or with a reversible cause, pacing should be deferred.

In patients with sinus bradycardia due to drugs like beta blockers or digoxin, simple discontinuation of these agents is adequate. In some cases, a change in medications or reduction in dose may be beneficial. Some patients on digoxin may have an extended period of symptomatic bradycardia and these patients may benefit from temporary transvenous pacing and/or IV atropine.

In patients with post infectious bradycardia, recovery often takes a long time and in some cases may not occur. Permanent pacing is recommended in these individuals.

Patients with hypothermia who have sinus bradycardia should not be administered atropine because it can cause irritation of the myocardium and generation of ectopic beats. Rather, these patients fully recover with supportive treatment and rewarming measures. Sinus bradycardia is a common observation during open-heart surgery, esp. during the cooling process. If perfusion of organs remains normal, then no specific treatment is recommended. Those who develop inadequate organ perfusion may require atropine, pressor support and temporary pacing.

Patients with sleep apnea who develop sinus bradycardia usually require multifaceted treatment including weight loss, use of CPAP and rarely surgery.

In all patients with sinus bradycardia who are admitted to the hospital, it is important to have an intravenous line and a vial of atropine at the bedside, in case of an emergency. Once the patient’s condition has stabilized, he/she may be discharged and followed up a general practitioner.

Drug therapy

In general, sinus bradycardia is not treated with medications unless the patient has symptoms. In all symptomatic patients, any underlying electrolyte deficiency including hypoxia should be corrected. The drug of choice in symptomatic patients is atropine given intravenously. In the past, isoproterenol was frequently used to treat sinus bradycardia but its use has declined over the years because of adverse effects.

Pacing

If the cause of sinus bradycardia is felt to be temporary then one may utilize either transcutaneous or transvenous pacing. This can be done at the bedside and can help stabilize the symptomatic patient. If the cause is felt to be irreversible, then a permanent pacemaker should be inserted [10].

Permanent pacemakers are inserted by both cardiologists and cardiac surgeons. The procedure is performed under local anesthesia and use of fluoroscopy. The type of pacemaker inserted depends on the patient’s medical condition, age, comorbid conditions and cost.

Prognosis

The prognosis for patients with sinus bradycardia depends on the cause. Patients who develop the disorder after exposure to a drug or toxic chemical usually have a good prognosis if the offending agent is removed. Those patients who have a structural defect in the sinus node have a guarded prognosis and may require a pacemaker if they are symptomatic. Patients who develop sinus bradycardia after open-heart surgery or hypothermia generally have a good prognosis as they do tend to recover with time.

Etiology

The causes of sinus bradycardia include the following:

Risk factors

The most significant factors for development of sinus bradycardia are advanced age, use of certain medications and open-heart surgery. Other risk factors that have been identified that increase the risk of bradycardia include:

Epidemiology

The exact number of individuals with sinus bradycardia is not known because many who have no symptoms never come to medical attention. Data from cardiology clinics reveal that the frequency may be anywhere about 1 in 10,000 individuals. These numbers are under estimates [2].

Sex distribution
Age distribution

Pathophysiology

Sinus bradycardia is not always pathological as it may be an incidental observation in young healthy adults or in those who are asleep. Most cases of sinus bradycardia are associated with an increase in vagal nerve activity. An increase in vagal tone is often a normal finding in well-conditioned athletes [3]. Pathological causes of sinus bradycardia include electrolyte deficiencies, inferior wall myocardial infarction, hypothyroidism, hypothermia, hypoglycemia, adverse drug effects, sepsis, sleep apnea [4] and elevated intracranial pressure (5).

Another very common cause of sinus bradycardia is due to an inability of the sinus node to generate an action potential in the atria. Also referred to as sick sinus syndrome, this disorder may present with symptoms related to under perfusion of the brain. In addition, sick sinus syndrome may present with alternating periods of tachycardia and bradycardia. Sick sinus syndrome is most common in elderly individuals who tend to have associated heart disease (6). The disorder has an unpredictable course with varied symptoms. Research in patients with sick sinus syndrome has revealed that some individuals have a quantitative decrease in sinus nodal neural cells and others have a variety of antinodal antibodies circulating in blood. Overall, the most cases of sick sinus syndrome are idiopathic.

It is very rare for sinus bradycardia to progress into heart block. Sudden death or cardiac arrest are rare events in people with sinus bradycardia.

Prevention

To prevent sinus bradycardia one should avoid use of illicit agents, eat a healthy diet, exercise regularly and not smoke. Excessive alcohol consumption is not recommended.

Summary

When the resting heart rate is 60 beats per minute or less, it is defined as sinus bradycardia. Fortunately most patients do not develop symptoms until the heart rate drops to less than 45-50 beats per minute. In most cases, sinus bradycardia is diagnosed incidentally when evaluating a patient for some different disorder [1] [2].

Patient Information

Bradycardia is defined as a heart rate of under 60 beats per minute. In most cases, sinus bradycardia is diagnosed incidentally. Common symptoms are shortness of breath, lightheadedness, dizziness, vertigo, and syncope.

Prior to discharge the patient must be educated about the disorder and what symptoms to watch out for. Most patients are able to follow up with their primary care physician. In cases where the sinus bradycardia is recurrent, a consultation should be made with a cardiologist. All patients should be told to return to the ED if they develop syncope, dizziness, chest pain and shortness of breath. Even after a permanent pacemaker has been inserted, long term follow up is required because the battery may wear out and needs replacement.

Patients should be educated about endocarditis prophylaxis if they have a permanent a pacemaker inserted.

References

Article

  1. Durham D, Worthley LI. Cardiac arrhythmias: diagnosis and management. The bradycardias. Crit Care Resusc. 2002;4(1):54-60.
  2. Kumar P, Kusumoto FM, Goldschlager N. Bradyarrhythmias in the elderly. Clin Geriatr Med. 2012;28(4):703-15.
  3. McClaskey D, Lee D, Buch E. Outcomes among athletes with arrhythmias and electrocardiographic abnormalities: implications for ECG interpretation. Sports Med. 2013;43(10):979-991
  4. Holty JE, Guilleminault C. REM-related bradyarrhythmia syndrome. Sleep Med Rev. 2011;15(3):143-51.
  5. Liu EF, Chen L, Gao BX. Sinus bradycardia: normal phenomenon or risk factor? Evaluation based on recent evidence. J Insur Med. 2012;43(2):102-11.
  6. Semelka M, Gera J, Usman S. Sick sinus syndrome: a review. Am Fam Physician. 2013;87(10):691-6.
  7. Deal N. Evaluation and management of bradydysrhythmias in the emergency department. Emerg Med Pract. 2013;15(9):1-15;
  8. Alboni P, Gianfranchi L, Brignole M. Treatment of persistent sinus bradycardia with intermittent symptoms: are guidelines clear? Europace. 2009;11(5):562-4.
  9. Seiler J. Treatment of bradycardias - who needs a pacemaker?. Ther Umsch. 2014;71(2):105-10
  10. Vardas PE, Simantirakis EN, Kanoupakis EM. New developments in cardiac pacemakers. Circulation. 2013;127(23):2343-50.

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Last updated: 2018-06-22 06:42