Friday, June 23, 2017

Approach to Bradycardia

Approach to Bradycardia

Last week we discussed an approach to bradycardia at morning report.

When there is an abnormality in a vital sign, the first step is to ensure stability.  

1.       Assess the ABCs, get monitors on, IV access
a.       Bradycardia is defined as a heart rate less than 60 beats per minute
2.       Ask yourself, is this unstable bradycardia?
a.       If yes à go down the unstable bradycardia ACLS algorithm
b.      If no à there is time to perform a focused history, physical and get investigations
3.       How do you define unstable bradycardia?
a.       Bradycardia that is causing one of the following symptoms:
                                                               i.      Hypotension
                                                             ii.      Acute altered mental status
                                                            iii.      Signs of shock
                                                           iv.      Ischemic chest discomfort
                                                             v.      Acute heart failure
4.       If there is unstable bradycardia, follow the ACLS algorithm including considering:
a.       Atropine
b.      Transcutaneous pacing
c.       Dopamine or epinephrine infusions
5.       If it is stable bradycardia, there is time to collect more information with a focused history, physical and get investigations
6.       An ECG is a key investigation!
7.       Two main question are:
a.       What type of rhythm is it?
b.      What is causing the bradycardia?



Rhythms associated with bradycardia

Bradycardia is an umbrella term that means that the heart rate is less than 60 beats per minute. But there can be several different rhythms that can cause a heart rate of less than 60 bpm.

-          Bradycardias can be classified narrow complex or wide complex (and as regular or irregular)

Narrow complex bradycardias

-          Sinus bradycardia
-          Junctional bradycardia
-          Sinus-node dysfunction
-          Second degree AV block, type I or II
-          Complete AV block (third degree AV block) with junctional escape
-          Atrial flutter or atrial fibrillation with high degree block/slow ventricular response

Wide complex bradycardia

-          Idioventricular rhythm
-          Complete AV block (third degree AV block) with ventricular escape
-          Any other causes of narrow complex bradycardia with aberrancy or bundle branch block

Causes of bradycardia

There are many causes of bradycardia. While not a fully inclusive list, causes can include:

Cardiac disease

-          Myocardial ischemia/MI
-          Myocarditis
-          Cardiomyopathies
-          Congenital disorders (such as muscular dystrophy)

Metabolic

-          Electrolyte disturbances (i.e. hypo- or hyper-kalemia)
-          Hypothyroidism
-          Hypothermia

Drugs

-          Medications (i.e. digoxin, beta blockers, calcium channel blockers, etc)
-          Toxidromes (cholinergic)

Iatrogenic

-          Post-cardiac procedure, surgery or transplantation  

Infectious

-          Endocarditis
-          Lyme disease
-          Typhoid fever
-          Chagas Disease

Autoimmune

-          Systemic lupus erythematosus
-          Rheumatoid arthritis
-          Scleroderma

Infiltrative

-          Sarcoidosis
-          Amyloidosis
-          Hemochromatosis

Physiological causes

-          Athletes
-          Vagal stimuli

Other causes

-          Hypoxia
-          Obstructive Sleep Apnea
-          Increased intracranial pressure (i.e. Cushing response)

References:

1.       Mangrum JM, DiMarco JP. The evaluation and management of bradycardia. N Engl J Med. 2000;342(10):703-9.
2.       Life in the Fastlane. Bradycardia. https://lifeinthefastlane.com/resources/bradycardia-ddx/


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