CASE

The patient is a spry, 79-year-old retired dentist who presented to the emergency department (ED) via emergency medical services (EMS) with an unwitnessed episode of passing out at home. The patient took atorvastatin (Lipitor) and a baby aspirin daily. He was living independently and in excellent health. Before this episode, he felt well and had no incontinence or involuntary limb movement observed by his wife. No neurologic or musculoskeletal deficit was observed following this episode, which was the first episode of its kind.

Vital signs on the EMS run sheet were BP, 131/64 mm Hg, with a regular heart rate of 61 beats per minute. The patient was afebrile, alert, and oriented  3; he did not appear ill. In the ED, he had no significant murmur, gallop, or rub. He had a regular rate and rhythm with normal breath sounds to both lungs. No focal neurologic or musculoskeletal deficit was observed, and orthostatic vital signs lying, sitting, and standing were completely unremarkable. Telemetry results, with the exception of occasional premature ventricular contractions, showed normal sinus rhythm without any significant arrhythmia. The ECG demonstrated a normal axis, and the QT interval was without any acute ST-segment or T-wave changes or changes consistent with an old or remote injury (see Figure 1).

Figure 1: The patient's ECG

WHAT IS YOUR DIAGNOSIS?

  • Stroke
  • Transient ischemic attack
  • Acute MI
  • Hypersensitive carotid sinus syndrome

DISCUSSION

This patient had hypersensitive carotid sinus syndrome, which is characterized most frequently by ventricular asystole caused by cessation of atrial activity from sinus arrest or sinoatrial exit block. Atrioventricular (AV) block is observed less frequently. In symptomatic patients, AV junctional or ventricular escapes generally do not occur or are present at very slow rates.1 Permanent pacing may be indicated for some types of neurally mediated syncope, which includes carotid sinus hypersensitivity and vasovagal syncope.2,3

Even if a hyperactive carotid sinus reflex is elicited in patients, particularly in older patients who complain of syncope or presyncope, the hyperactive reflex elicited with carotid sinus massage may not necessarily be responsible for these symptoms. Direct pressure or extension of the carotid sinus from head turning, neck tension, and tight collars can also be a source of syncope by reducing blood flow through the cerebral arteries. The mechanism responsible for hypersensitive carotid sinus reflex is not known,1 although the condition is most commonly associated with coronary artery disease.

Because AV block can occur during periods of hypersensitive carotid reflex, some form of ventricular pacing, with or without atrial pacing, is generally required. Atropine and pacing do not prevent the decrease in systemic BP in the vasodepressor form of carotid sinus hypersensitivity, which may result from inhibition of sympathetic vasoconstrictor nerves and possibly from activation of cholinergic sympathetic vasodilator fibers. Combinations of vasodepressor and cardioinhibitory types can occur, and vasodepression can account for continued syncope after pacemaker implantation in some patients.

Patients who have a hyperactive carotid sinus reflex that does not cause symptoms require no treatment. Drugs such as digoxin (Lanoxicaps, Lanoxin), methyldopa (Aldochlor, Aldoril), clonidine (Catapres, Clorpres, Duraclon), and propranolol (Inderal) can enhance the response to carotid sinus massage and be responsible for symptoms in some patients.1 JAAPA

Bradley Orville works at Cardiovascular Clinical Associates of Farmington Hills, Michigan. He has indicated no relationships to disclose relating to the content of this article.

Erich Fogg, PA-C, MMSc, department editor

REFERENCES

1. Specific arrhythmias: diagnosis and treatment. In: Libby P, Bonow RO, Mann DL, Zipes DP. Braunwald's Heart Disease: A Textbook of Cardiovascular Medicine. 8th ed. Saunders; 2007: chap 35.

2. ACC/AHA guidelines for implantation of cardiac pacemakers and antiarrhythmia devices. J Am Coll Cardiol. 1998;31(5): 1175-1209.

3. ACC/AHA/NASPE 2002 guideline update for implantation of cardiac pacemakers and antiarrhythmia devices: summary article. Circulation. 2002;106(16):2145-2161.