How Is Bradycardia Diagnosed?
Bradycardia, a heart rate <60, may be normal in athletes or during sleep. Abnormal bradycardias result in unpleasant symptoms subjectively and possible life-threatening risks objectively. In diagnosing whether a bradycardia is normal or abnormal, a history and physical and an electrocardiogram are key components in exploring a lower-than-normal heart rate.
The first step is to confirm that a bradycardia is anything other than an adaptive sinus bradycardia, such as is seen in athletes. Is not uncommon for a very conditioned athlete to have a resting pulse of <60 beats per minute. This is a normal type of sinus bradycardia and is fairly easy to conclude with a history.
- Elderly patients may have bradycardia as an early sign of senescent sick sinus syndrome (SSS)
- The elderly, who are more likely to be taking several medications, are more at risk for bradycardia as a side effect to any one of them or a combination
- A history of coronary artery disease puts the blood supply to the SA node at risk
- Those with neurological disorders may have increased intracranial pressure, which can cause bradycardia
There is no specific heart rate below which all patients complain of symptoms, but vital signs are often closely related to what they may be experiencing. Certainly, a pulse <60 meets the definition of bradycardia. The rhythm of the pulse is telling and can be diagnostic depending on whether it is regular, irregular with patterns (“regular” irregular), or irregular without patterns (“irregular” irregular).
Blood pressure that indicates hypotension or compensatory normotension can assign the severity of danger a patient with arrhythmia may have.
Auscultation of the chest can reveal corroborating findings such as abnormal heart sounds, irregularly spaced heart sounds, or sounds indicating turbulence. The lungs can be evaluated in the context of COPD or other ventilatory conditions that may impact the rate and rhythm of the heart.
If bradycardia is abnormal, nothing will prove this better than an ECG, and nothing is more diagnostic than when an arrhythmia is identified as the cause of the bradycardia. The ECG will serve to
- Confirm whether the bradycardia is a sinus bradycardia
- Determine whether there is only one or more than one pacemaker
- Identify atrioventricular block of the normal electrical conductive pathway and where that block is occurring
- Identify any evidence of myocardial infarction that impacts the SA or AV nodes or other tissue along the conductive pathways
- Echocardiography, to identify possible chamber size abnormalities, valvular problems, or other causes or results of pathology
- Electrophysiologic testing is more in-depth than an ECG and can identify subtleties when the ECG is not helpful
- Blood tests can screen for hypothyroidism, electrolyte abnormalities, and other reversible causes of bradycardia