Patent foramen ovale, dialysis and microembolization

Haemodialysis (HD) circuits are known to produce microemboli. Patent foramen ovale (PFO) may be important in HD patients by allowing right to left intracardiac shunting of microemboli (blood clots or microbubbles), which may pass into the cerebral circulation.

We undertook bubble contrast transthoracic echocardiography to identify PFO in HD patients and in a control population of peritoneal dialysis patients. We interrogated draining arteriovenous fistulae to confirm that microemboli are created during HD. We then undertook transcranial Doppler scanning of the middle cerebral artery before and during dialysis, with and without Valsalva augmentation, to detect cerebral microemboli in HD patients and in the control group.

Eighty patients (age 60.4 ± 15.0 years) were recruited to the study. In 12 of 51 HD patients and five of 29 peritoneal dialysis patients a PFO was found (21.3%). Ultrasound scanning of draining arteriovenous fistulae showed a significant difference in the number of microemboli before (1.63 ± 3.47 hits per 5 min) and during (31.6 ± 28.9 hits per 5 min) HD (P = 0.012). However, there was no evidence of microembolization to the middle cerebral artery before or during HD in the study or control groups.

Although microemboli are detectable in the draining arteriovenous fistulae of patients undergoing HD, there was no evidence of cerebral microembolization in the middle cerebral artery during HD in those with or without a PFO. The results contrast with previous reports demonstrating microemboli in the carotid circulation during HD.