Cannon A Wave
An 81-year-old woman with a history of controlled hypertension and hypercholesterolemia was admitted because of progressive dizziness for 5 days, having been hospitalized for the same problem 2 years previously. Normal coronary angiogram, normal sinoatrial nodal function, and normal atrioventricular conduction were confirmed at that time. Before this latest hospitalization, her family found out that her average heart rate was <50 bpm. She also had poor appetite for a couple of weeks with vomiting and nausea 2 days before admission. She developed intermittent chest tightness, chest pain, palpitation, shortness of breath, and chills. The symptoms progressed, but the patient experienced no fever or diarrhea. In the emergency room, vital signs were blood pressure 205/40 mm Hg, heart rate 50 bpm, respiratory rate 20/min, and body temperature 36.4°C. Consciousness was clear and well oriented. Feet and hands were cold, and the pulse of both dorsal pedals was bounding, regular, and slow. Jugular vein wave varied and showed a pulse-like “Cannon A” wave (Figure 1; online-only Data Supplement Movie I).
In the emergency room, serum sodium level was 129 mEq/L and serum potassium level was 2.8 mEq/L. Serum creatinine level was 1.4 mg/dL. Hemoglobin was 12.5 gm/dL. Serum troponin-I and creatinine kinase levels were within normal range. ECG revealed complete atrioventricular block with slow junctional escape rhythm (Figure 2). During the first week of hospitalization, her hyponatremia and hypokalemia were corrected. Isoproterenol infusion was given, but the atrioventricular block persisted. An electrophysiology study revealed intermittent infra-His block and no ventriculoatrial conduction during ventricular pacing (Figure 3). DDD-R pacemaker was implanted in due course, and the lower rate of pacing was set at 80 bpm. The cannon A wave disappeared (online-only Data Supplement Movie II).
Cannon A wave occurs with atrioventricular dissociation and right atrial contraction against a closed tricuspid valve. Large A waves are associated with reduced right ventricular compliance or elevated right ventricular end-diastolic pressure. The differential diagnoses of cannon A wave were atrial, ventricular, or junctional premature beats, ventricular tachycardia, severe tricuspid stenosis, first-degree atrioventricular block with a markedly prolonged PR interval, high-grade atrioventricular block, and atrioventricular dissociation.
The online-only Data Supplement is available with this article at http://circ.ahajournals.org/cgi/content/full/119/13/e381/DC1.