A 62-year-old man is admitted with chronic obstructive pulmonary disease (COPD) and mild left ventricular (LV) dysfunction (ejection fraction [EF] 45%) as well as symptomatic, recurrent atrial fibrillation (heart rate [HR] 120s to 150s) despite antiarrhythmic drug therapy and direct current cardioversion in the past. After rate control with intravenous (IV) βblockers, the HR improves and the patient feels better. Given his recurrent atrial fibrillation despite optimal medical therapy, the patient is referred for radiofrequency ablation of atrial fibrillation (pulmonary vein isolation) procedure. The procedure is performed on anticoagulation (international normalized ratio >2.0) and is deemed a success, with no inducible atrial fibrillation at the end of the case. A small atrial septal defect (ASD) was noted with intracardiac echocardiography at the end of the case, with no other remarkable findings. That evening in the post-anesthesia care-unit (PACU), the patient is noted to be hypotensive and tachycardic with increasing dyspnea. There is a concern for cardiac tamponade; however, the arterial line does not show a significant respiratory variation of the blood pressure (BP) waveform (pulsus paradoxus). An echocardiogram is performed, demonstrating a large circumferential effusion and the patient is referred for urgent pericardiocentesis.
Which of the following explains why the patient did not develop a pulsus on the arterial line, despite a large, hemodynamically significant pericardial effusion?
A. Presence of an ASDPresence of an ASD. The presence of the iatrogenic ASD after the transseptal puncture for the radiofrequency ablation/pulmonary vein isolation procedure equates right atrial (RA) and left atrial (LA) pressures with inspiration. The predicted decrease in LV filling during inspiration due to interventricular dependence and exaggerated RV filling and septal shift toward the LV is mitigated by the presence of an ASD. With inspiration, the decrease in intrathoracic pressure is transmitted to both atria and thus preload to the LV is maintained and interventricular dependence is not as pronounced. Thus, the variation in systolic blood pressure is not as prominent, resulting in minimal to no pulsus paradoxus. Administration of excess fluid would stave off circulatory collapse in tamponade; however, it would not diminish the pulsus. Answer b is incorrect as with severe LV dysfunction, patients can have a pulsus alternans (variation in peak systolic pressure with every other beat) and Answer c is incorrect as obstructive lung disease can lead to the presence of a pulsus due to exaggerated inspiratory effort and negative intrathoracic pressure.