Cannon Wave Revisited

Case Report

A 20-year-old female with a history of congenital heart block requiring a pacemaker at age 11 presented with intermittent chest pain, lightheadedness and progressive fatigue. She had been diagnosed with congenital third-degree heart block at the age of two and a half years, requiring atrioventricular (AV) sequential permanent pacing for symptomatic relief (Figure 1). She was in her usual state of health until the day of admission. She presented to the emergency room with fatigue, weakness, dizziness and near-syncope associated with intermittent chest wall pain. Physical examination was unremarkable and pulse rate was regular. The jugular venous pulsation was notable for intermittent Cannon A waves. Her laboratory testing and chest X-ray were unremarkable, but her 12-lead electrocardiogram was significant for VVI pacing at 65 beats per minute (Figure 2). Interrogation of her permanent pacemaker showed that it was at the end of life due to battery depletion.

During her pacemaker revision, she had satisfactory atrial and ventricular pacemaker lead function inspected by fluoroscopy and the pacing system analyzer (PSA). Her permanent pacemaker pulse generator was replaced and programmed to the initial DDD mode (Figure 3), which resulted in immediate resolution of her symptoms. Her symptoms were reproduced after her pacemaker was temporarily programmed to VVI mode. Her blood pressure during VVI mode pacing at the rate of 65 bpm was only 80/50 mm Hg, and with DDD mode at the rate of 65 bpm, blood pressure improved to 110/60 mm Hg. Furthermore, no jugular Cannon A waves were noted in the immediate post-operative period, and she was discharged the next day in stable condition. 

DISCUSSION

Congenital complete atrioventricular block (CCAVB) is an uncommon cardiac conduction defect occurring in 1 of every 20,000 live births.¹ Although spontaneous recovery from CCAVB is reported, unpredictable Stokes-Adams attacks with considerable mortality during the first episode are more likely.² The mortality in children with isolated congenital complete heart block is estimated at 8-16% in infants and 4-8% in children and adults.³ Cardiac pacing support in newborns is indicated in congenital heart block, which can manifest as congestive heart failure, wide complex ventricular tachycardia, symptomatic bradycardia, and syncope. 

Pacemaker syndrome is the hemodynamic instability caused by uncoupled or inappropriate ventricular pacing due to loss of AV synchrony, which is most commonly seen with VVI mode in patients with intrinsic atrial activity.⁵ It can present as generalized malaise, dizziness, syncope and near-syncope. The most striking clinical finding is the Cannon A wave in the jugular venous pulsation (Figure 4), which results from AV dissociation causing atrial contraction against closed AV valves. 

Since atrial contraction contributes up to 20% of ventricular filing, AV dyssynchrony could lead to compromised ventricular function, resulting in a lower cardiac output and even congestive heart failure in some patients. Consequently, hypotension, tachycardia, tachypnea, low oxygen saturation, crackles, hepatomegaly, ascites, and pedal edema may be observed and could be treated with AV sequential pacing in order to restore AV synchrony.⁶

In our patient, switching to VVI mode occurred when her permanent pacemaker battery reached near end of life, and her symptoms resolved after her pulse generator was replaced, resulting in restoration of AV synchrony.

CONCLUSION

Pacemaker syndrome, resulting from AV dyssynchrony in a pacemaker-dependent patient, can present with alarming clinical features such as pre-syncope, hypotension, and other signs of congestive heart failure. One characteristic feature is the Cannon A wave in the jugular venous pulsation. One should be aware of the etiology, since establishing AV synchrony can resolve the acute symptoms and help improve cardiac function. 

Disclosure: The authors have no conflicts of interest to report regarding the content herein. 

References

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4. Cannon BC. Pediatric arrhythmias. In: Murphy JG, Lloyd MA, ed. Mayo Clinic Cardiology: Concise Textbook, 4th edition. New York: Oxford University Press; 2012:266-269.
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