SVT and cocaine use

Let’s start by asking ourselves: Is the rhythm a true re-entrant SVT or simply sinus tachycardia driven by cocaine-induced sympathetic excess.

Firstly, let’s look at primary SVT versus secondary SVT.

1. Primary SVT is an intrinsic supraventricular arrhythmia in which the tachycardia is the disease process itself. It is usually caused by a re-entrant circuit or abnormal automatic focus within the atria or AV node.

Examples:

• AV Nodal Re-entrant Tachycardia (AVNRT)
• AV Re-entrant Tachycardia (AVRT, e.g., WPW)
• Focal Atrial Tachycardia
• Some cases of atrial flutter with rapid conduction

Typical features:

• Sudden onset and sudden termination
• Very regular rhythm
• Often fixed rate (commonly 150-250 bpm)
• Minimal relationship to physiologic stress
• Often recurrent episodes
• Usually responds to vagal maneuvers or adenosine if AV node-dependent

Management focus: terminate the arrhythmia (vagal maneuvers, adenosine, cardioversion when appropriate).

2. Secondary SVT occurs because another underlying condition is driving the tachycardia. The rhythm may be sinus tachycardia or occasionally a true atrial tachyarrhythmia precipitated by physiologic stress.

Common causes:

• Cocaine or other stimulant toxicity
• Sepsis
• Hypovolemia/hemorrhage
• Fever
• Hypoxia
• Pulmonary embolism
• Hyperthyroidism
• Pain, anxiety, agitation
• Heart failure

Typical features:

• Gradual onset and offset
• Rate fluctuates with patient condition
• Clinical signs point toward an underlying cause
• Adenosine may provide diagnostic information but usually does not treat the root problem

Management focus: treat the underlying cause.

Primary SVT: "The rhythm is causing the problem."

Secondary SVT/tachycardia: "The patient has a problem that is causing the rhythm."

In a patient with recent significant cocaine use, chest pain, SOB, and a narrow-complex tachycardia, the overall clinical picture should raise concern for a sympathomimetic toxidrome. Benzodiazepines are generally considered first-line therapy for cocaine toxicity because they reduce central sympathetic outflow, often improving tachycardia, hypertension, agitation, and chest pain simultaneously.

That said, adenosine is not contraindicated simply because the patient used cocaine. If the rhythm is truly AV-node dependent SVT (AVNRT/AVRT), adenosine should still terminate it.

Features suggesting sinus tachycardia from cocaine toxicity:

• Recent cocaine use with ongoing sympathomimetic findings (not a complete list):
• Tachycardia
• Chest pain
• Agitation/Anxiety
• Diaphoresis
• Hypertension
• Dilated pupils
• Tremors
• Heart rate that is elevated but varies somewhat with stimulation or activity.
• Clear sinus P waves preceding each QRS.
• Rate typically in the 110-170 range rather than abruptly fixed.
• No history of sudden onset/palpitation episode.

In this situation, treating the toxidrome with benzodiazepines and supportive care addresses the underlying cause. Adenosine is unlikely to be beneficial because the rhythm is not AV-node dependent. There is currently no medical directive in the ALS PCS that addresses this and a patch to a base hospital physician would be required.

Features suggesting true SVT:

• Abrupt onset reported by the patient ("it suddenly started")
• Very regular rhythm
• Rate often 150-250 bpm
• P waves absent, buried, or retrograde
• Previous episodes of SVT
• No significant beat-to-beat variation in rate

In this case, vagal maneuvers and adenosine remains appropriate treatments for a stable narrow-complex regular tachycardia. Cocaine use does not change the electrophysiologic mechanism of AVNRT/AVRT.

One tip to consider, a rate near 180 with a perfectly regular rhythm and no discernible sinus P waves is harder to attribute to simple sinus tachycardia and should raise suspicion for SVT.

In conclusion, if the patient presentation looks like cocaine-induced sympathomimetic toxicity with sinus tachycardia, prioritizing treatment of the toxidrome (benzodiazepines, supportive care, ACS assessment and treatment) because that addresses the underlying problem, but if the ECG and history are convincing for a regular narrow-complex SVT, adenosine is still appropriate and should work despite the use of cocaine.