Adenosine-A drug with myriad utility in the diagnosis and treatment of arrhythmias

Abstract

Adenosine has been used in the emergency treatment of arrhythmia for more than nine decades. However, cardiologists are often unfamiliar about its basic mechanism and various diagnostic and therapeutic uses, considering it mainly as a therapeutic drug for supraventricular tachycardia. This article discusses the role of adenosine relevant to emergency physicians, cardiologists, and electrophysiologists. Understanding of the mechanisms of adenosine and its electrophysiological effects is discussed first, followed by dosing, side effects, diagnostic, and therapeutic uses. Finally, the role of adenosine in the electrophysiology laboratory is discussed.

Keywords: anti‐arrhythmic drugs; atrioventricular block; supraventricular tachycardia; ventricular tachycardia.

FIGURE 1

Effect of adenosine on cardiac cells through A1 receptors can be either cAMP‐dependent or independent. Activation of potassium channels (negative chronotropy and dromotropy) is cAMP‐independent while inhibition of hyperpolarization‐activated (funny I_f) current (phase 4 depolarization) and I_CaL are cAMP‐dependent. The figure is adapted from Lerman et al ¹²

FIGURE 2

Effect of adenosine on SA node in red. Adenosine leads to hyperpolarization (dotted line ‐ red color) of the resting membrane potential; therefore, decreases phase 4 slope of diastolic depolarization. Excessive hyperpolarization can lead to sinus arrest (Dotted line ‐ brown color). It also inhibits hyperpolarization‐activated (funny I_f) current (phase 4 depolarization) and I_CaL (Phase 1) as an indirect effect through cAMP inhibition in the presence of sympathetic stimulation

FIGURE 3

Effect of adenosine on the atrium on the left and atrioventricular (AV) node on the right. Adenosine decreases action potential duration (APD) hence refractory period of atrium without any effect on resting membrane potential (RMP) while decreasing RMP (more negative) of AV node without any effect on APD. [Red is the effect of adenosine and black is control]. The figure is adapted from the Lerman et al ¹⁵

FIGURE 4

Preexcitation being unmasked by adenosine in a young male with a history of palpitations without documented tachycardia. The delta waves are negative in leads II/III and positive in V1; this was a left posterior accessory pathway, later ablated successfully

FIGURE 5

Atrioventricular nodal echo (retrograde P wave at the end of the QRS complex) during the adenosine test, shown by an arrow, which is preceded by a PR jump (denoted by numbers in milliseconds) ³⁷

FIGURE 6

Narrow QRS tachycardia with intermediate RP interval terminates with a P wave after adenosine, suggesting AVRT. Ectopics followed by sinus arrest are seen after termination, both of which are common after adenosine. Later, preexcitation is seen suggestive of a left free wall pathway which was inapparent during tachycardia

FIGURE 7

Atrial tachycardia/atrial flutter being unmasked by adenosine. The initial part shows 1:1 AV conduction, followed by a complete AV block. Later, the arrhythmia degenerates into atrial fibrillation (better seen in lead aVF)

FIGURE 8

On the left side of the tracing there is narrow complex tachycardia with long RP interval with P waves (slanting arrow) which are positive in inferior leads ruling out AVRT and AVNRT. Also, narrower as compared to sinus beats (circle). Tachycardia terminates after a QRS complex (arrow) suggestive of adenosine sensitive atrial tachycardia

FIGURE 9

Role of adenosine in the differential diagnosis of Narrow QRS tachycardia ⁴⁴

FIGURE 10

Electrocardiogram monitor strips. Panel A shows pre excited atrial fibrillation. Adenosine (12 mg) denoted by an arrow was administered in the emergency department. Panel B shows the development of ventricular fibrillation after adenosine administration ²⁴

FIGURE 11

ECG in the initial part shows WQRST with RBBB morphology in V1 and an inferior axis. Differential diagnoses are a pre excited tachycardia and ventricular tachycardia. Adenosine leads to the termination of tachycardia, following which preexcitation with an identical QRS is seen, followed by AV block. This was an antidromic tachycardia due to the adenosine‐sensitive accessory pathway