A 68-year-old man comes to the emergency department due to palpitations accompanied by mild dizziness and sweating. The symptoms started abruptly 30 minutes ago. He has had no chest pain or shortness of breath. Medical history is significant for hypertension and a myocardial infarction 6 months ago. The patient is an ex-smoker with a 30-pack-year history. Blood pressure is 102/65 mm Hg and pulse is 160/min and regular. Oxygen saturation is 98% on 2 L nasal cannula oxygen. On physical examination, prominent, high-amplitude jugular venous pulsations are seen intermittently at irregular intervals. ECG reveals a regular, wide-complex tachycardia. Which of the following best explains the patient's physical findings?
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This patient with palpitations has a history of ischemic heart disease (ie, myocardial infarction), placing him at increased risk for ventricular arrhythmia; his ECG reveals a regular, wide-complex tachycardia consistent with ventricular tachycardia. Cardiac arrhythmias often alter the waveform of jugular venous pulsation (JVP), which is representative of the hemodynamic changes in the right atrium throughout the cardiac cycle. Normal JVP consists of 3 waves that correspond to increases in right atrial pressure:
A wave caused by right atrial contraction, closely followed by tricuspid valve closure
C wave caused by right ventricular contraction against a closed tricuspid valve
V wave, representing the peak of right atrial filling, just prior to reopening of the tricuspid valve
Cannon A waves, as seen in this patient, are intermittent, prominent A waves caused by the surge in jugular venous pressure that occurs due to right atrial contraction against a closed tricuspid valve; these waves can be seen with any arrhythmia involving atrioventricular dissociation, such as ventricular tachycardia, which is characterized by self-propagation within the ventricles without communication with the atria.
Other arrhythmias in which cannon A waves are commonly seen include complete atrioventricular block and frequent premature ventricular contractions. Patients may sometimes report symptoms associated with cannon A waves, including headache, jaw pain, and sensation of neck pulsation.
(Choice A) Left-sided valvular disease (eg, aortic regurgitation) does not typically affect the shape of the JVP waveform; however, severe disease can lead to decompensated heart failure and an increase in baseline jugular venous pressure (the entire waveform is shifted upward).
(Choice B) Atrial fibrillation causes an absent A wave on the JVP waveform because there is no organized atrial contraction. ECG would show an irregularly irregular rhythm.
(Choice D) Pericardial effusion may lead to cardiac tamponade (eg, hypotension, dilated neck veins, muffled heart sounds), which can cause a flattened y descent due to external right ventricular compression with restricted diastolic filling.
(Choice E) Tricuspid regurgitation causes a prominent V wave and absent x descent due to elevation of right atrial pressure throughout ventricular systole.
Educational objective:
The jugular venous pulsation waveform is representative of right atrial hemodynamics throughout the cardiac cycle. Cannon A waves are intermittent, prominent A waves caused by the surge in jugular venous pressure that occurs due to right atrial contraction against a closed tricuspid valve. These waves are indicative of a cardiac arrhythmia involving atrioventricular dissociation (eg, ventricular tachycardia, complete atrioventricular block).