A 62-year-old woman is in the cardiac surgery ICU, postoperative day one from a mitral valve repair and annuloplasty. She had been known to have severe symptomatic mitral regurgitation due to a prolapsed and flail valve, secondary to myxomatous degeneration. Following surgery, her condition has been stable:

• Ectopic atrial rhythm (atrial rate 51/min)
• AV dissociation with junctional escape rhythm (junctional rate 56/min)
• Occasional AV capture (the third and tenth QRS complexes) with first degree AV block
• Moderate voltage criteria for left ventricular hypertrophy

In this case there is AV dissociation because the ectopic atrial pacemaker is slower than the junctional pacemaker, which escapes. As the junctional pacemaker has a faster rate, the QRS moves ahead of the P and eventually the atrial depolarization reaches the AV junction when its refractory period is over and AV capture occurs. Note that there is a first degree AV block; the AV capture occurs with PR=320 msec.