What is the initial approach for atrioventricular (AV) blockade in managing supraventricular tachycardia?

Initial Management of Atrioventricular (AV) Blockade in Supraventricular Tachycardia

Vagal maneuvers should be used as first-line therapy for the initial approach to AV blockade in managing supraventricular tachycardia in hemodynamically stable patients. 1

First-Line Approach for Hemodynamically Stable Patients

• Vagal maneuvers (Valsalva and carotid sinus massage) should be performed with the patient in the supine position as the initial intervention to terminate SVT 1
• These maneuvers work by slowing conduction through the AV node, which can interrupt the reentry circuit in AVNRT (atrioventricular nodal reentrant tachycardia), the most common form of SVT 1
• If vagal maneuvers fail, IV adenosine is the next step in management due to its rapid onset and short half-life 1

Medication Management if Vagal Maneuvers Fail

• IV adenosine should be administered if vagal maneuvers are unsuccessful, as it temporarily blocks AV nodal conduction 1
• If adenosine is ineffective or contraindicated (e.g., severe asthma), IV calcium channel blockers (diltiazem or verapamil) or IV beta blockers should be used 1, 2
• Caution must be used with verapamil in patients with left ventricular dysfunction as it has negative inotropic effects that could precipitate heart failure 3

Algorithm for Medication Selection

1. First choice: IV adenosine (Class I recommendation) 1
2. Second choice: IV beta blockers or IV calcium channel blockers (Class IIa recommendation) 1
   • Beta blockers (e.g., metoprolol) are preferred in patients with good cardiac function 1, 4
   • Calcium channel blockers (verapamil/diltiazem) are alternatives, especially when beta blockers are contraindicated 1
3. Third choice: If the above fail, IV amiodarone may be considered (Class IIb recommendation) 1

Special Considerations

• Beta blockers are typically avoided in patients with severe bronchospastic pulmonary disease 1
• Both beta blockers and verapamil should be avoided in patients with acute decompensated heart failure or hemodynamic instability 1, 3
• Verapamil is contraindicated in patients with Wolff-Parkinson-White syndrome with pre-excited AF due to risk of accelerating ventricular response 3
• Avoid concomitant use of IV calcium channel blockers and beta blockers due to potential for severe hypotension and bradycardia 1

For Hemodynamically Unstable Patients

• Immediate synchronized cardioversion is indicated for patients with hemodynamic instability (Class I recommendation) 1, 5
• Initial energy of 50-100 J with biphasic waveform is recommended 5
• Increase energy in a stepwise fashion if initial shock fails 5

Long-term Management Considerations

• Catheter ablation has become the preferred therapy over long-term pharmacologic therapy for management of recurrent, symptomatic AVNRT 1, 2
• Success rates for slow pathway ablation exceed 96% with only a 1% risk of AV block 1
• For patients who decline ablation or are not candidates, oral beta blockers or calcium channel blockers can be used for long-term suppression 2, 6

Common Pitfalls to Avoid

• Misdiagnosing the type of SVT can lead to inappropriate treatment selection 7
• Administering verapamil to patients with WPW syndrome can be dangerous and potentially fatal 3
• Failure to recognize pre-existing conduction abnormalities before administering AV nodal blocking agents can result in high-degree heart block 3
• Using adenosine in patients taking dipyridamole can lead to prolonged effects due to potentiation 1