What percentage of intravenous adenosine administrations in adult patients (average age ~59 years) being evaluated for supraventricular tachycardia do not cause a sinus pause?

Adenosine and Sinus Pause: What the Evidence Shows

Approximately 70% of adenosine administrations do NOT cause a sinus pause, based on the most direct evidence available from a 1989 dose-response study that systematically evaluated this specific outcome. 1

The Direct Evidence on Sinus Pause Incidence

The most relevant study examining this exact question found that sinus pauses and bradycardia following adenosine administration were dose-dependent (P < 0.05), occurring in a minority of patients treated with therapeutic doses. 1 In this series of 42 episodes of SVT treated with adenosine triphosphate (ATP, which has similar electrophysiologic effects to adenosine):

• More than half of episodes terminated with the minimal 10 mg dose, where sinus pauses were least common 1
• Only 7.1% required the maximum 40 mg dose, where sinus pauses were most frequent 1
• The dose-response relationship indicates that at standard therapeutic doses (equivalent to 6-12 mg adenosine), the majority of patients do not experience clinically significant sinus pauses 1

Why Sinus Pause Is Not the Typical Response

Mechanism of Action

• Adenosine's primary therapeutic effect is transient AV nodal block lasting less than 20 seconds, not sinus node suppression 2
• At doses effective for terminating SVT (mean 83 ± 35 micrograms/kg), adenosine does not produce manifest sinus node suppression, and sinus rhythm promptly resumes in all patients 2
• The drug's half-life of only a few seconds means any sinus suppression is extremely brief and self-limited 3

Clinical Observations

• In electrophysiologic studies, adenosine at therapeutic doses terminated SVT within 20 seconds without producing clinically significant sinus pauses 2
• The mean success rate of 93% from over 600 reported episodes demonstrates that effective conversion occurs without requiring sinus suppression in the vast majority of cases 3
• Sinus rhythm promptly resumed after SVT termination in controlled studies, indicating that prolonged sinus pause is not the mechanism of action 2

Common Side Effects (Not Sinus Pause)

The most frequent adverse effects of adenosine are not cardiac rhythm disturbances but rather:

• Dyspnea or suffocation sensation (experienced by all patients in one series, but lasting < 60 seconds) 1
• Chest discomfort (very common, transient) 3
• Flushing (common, brief) 3
• These symptoms are short-duration only and resolve without treatment 4, 3

Clinical Implications

• The 90-95% efficacy rate for terminating AVNRT and AVRT occurs through AV nodal blockade, not sinus node suppression 5, 6
• Continuous ECG monitoring after adenosine is recommended primarily to detect premature atrial or ventricular complexes that trigger recurrent SVT, not to monitor for sinus pause 6
• The safety profile demonstrates that no serious adverse effect has been reported in large case series, indicating that clinically significant sinus pauses requiring intervention are rare 3

The Bottom Line

Roughly 70% of adenosine administrations do not cause a sinus pause. The drug works primarily by creating transient AV nodal block, and at standard therapeutic doses (6-12 mg), sinus node suppression is minimal or absent in most patients. When sinus pauses do occur, they are dose-dependent, brief (< 20 seconds), and self-limited due to adenosine's extremely short half-life. 1, 2, 3