What is the diagnosis and management of syncope with a possible cardiac cause in a patient with first-degree atrioventricular (AV) block?

From the Guidelines

Syncope with a possible cardiac cause and first-degree heart block requires prompt evaluation and management, with a focus on identifying potential arrhythmias or conduction abnormalities using a 12-lead ECG, echocardiogram, and 24-48 hour Holter monitoring, as recommended by the 2017 ACC/AHA/HRS guideline 1.

Initial Assessment

The initial assessment should include:

• A 12-lead ECG to identify potential arrhythmias or conduction abnormalities, such as bundle branch block or atrioventricular conduction disturbances, which can provide clues about the cause of syncope 1
• An echocardiogram to evaluate cardiac structure and function
• 24-48 hour Holter monitoring to detect intermittent arrhythmias or conduction abnormalities First-degree heart block (PR interval >200ms) alone rarely causes syncope, so it is essential to search for additional cardiac pathology, such as intermittent higher-degree blocks, sick sinus syndrome, or structural heart disease.

Management

Management depends on the underlying cause of syncope:

• If syncope is due to progression to higher-degree blocks, a permanent pacemaker may be indicated, as recommended by the 2018 ACC/AHA/HRS guideline on the evaluation and management of patients with bradycardia and cardiac conduction delay 1
• For vasovagal syncope with first-degree block as an incidental finding, education on trigger avoidance, increased fluid/salt intake, and physical counterpressure maneuvers are recommended
• Medications like midodrine (2.5-10mg three times daily) or fludrocortisone (0.1-0.2mg daily) may help in refractory cases Patients should temporarily avoid driving and high-risk activities until diagnosis is established. The 2013 ESC guidelines on cardiac pacing and cardiac resynchronization therapy also emphasize the importance of identifying the underlying cause of syncope and selecting the appropriate treatment, including cardiac pacing in patients with intrinsic intermittent AV block 1.

From the FDA Drug Label

Atropine also may lessen the degree of partial heart block when vagal activity is an etiologic factor In some patients with complete heart block, the idioventricular rate may be accelerated by atropine; in others, the rate is stabilized. Adequate doses of atropine abolish various types of reflex vagal cardiac slowing or asystole

Management of Syncope with Possible Cardiac Cause and First Degree Heart Block:

• Atropine may be used to lessen the degree of partial heart block when vagal activity is an etiologic factor 2.
• It can abolish reflex vagal cardiac slowing or asystole, which may be beneficial in patients with syncope and possible cardiac cause.
• However, its use should be cautious and individualized, as it may have varying effects on heart rate and rhythm.
• Key Considerations:
  • Atropine may accelerate the idioventricular rate in some patients with complete heart block.
  • It may stabilize the rate in others.
  • Large doses may cause atrioventricular (A-V) block and nodal rhythm.

From the Research

Diagnosis of Syncope with Possible Cardiac Cause

• Syncope is defined as a brief loss of consciousness due to an abrupt fall in cerebral perfusion 3.
• The classification of syncope is based on the underlying pathophysiological mechanism causing the event, and includes cardiac, orthostatic and reflex (neurally mediated) mechanisms 3.
• Cardiovascular causes of syncope may be structural (mechanical) or electrical 3.

First Degree Heart Block Diagnosis and Management

• A 12-lead electrocardiogram (ECG) is the only instrumental test recommended for the initial evaluation of patients with suspected syncope 4.
• The ECG may disclose an arrhythmia associated with a high likelihood of syncope, avoiding further evaluations and permitting institution of specific treatment in some patients 4.
• Certain electrocardiographic presentations in the patient with syncope will not only provide a reason for the loss of consciousness but also guide early therapy and disposition in this individual, including bradycardia, atrioventricular block, intraventricular conduction abnormality, and tachydysrhythmia 5.
• In patients with suspected cardiac syncope, monitoring is indicated until a diagnosis is made 6.

Management of Syncope with Possible Cardiac Cause

• Patients with life-threatening causes of syncope should be managed urgently and appropriately 3.
• Where heart disease is found to be the cause of the syncope, a specialist opinion is warranted and where possible the problem should be corrected 3.
• The main objectives of management are to prolong survival, limit physical injuries and prevent recurrences 3.
• Syncope units have been shown to improve the rate of diagnosis while reducing cost and thus are highly recommended 6.