Arteriovenous Malformation Draining Vein Physiology and Determinants of Transnidal Pressure Gradients

Abstract

ARTERIOVENOUS MALFORMATION (AVM) draining vein pressure (DVP) may have an influence on both the natural history of the disease and treatment outcome. The purposes of this study were to assess the relationship between DVP and other clinical and physiological variables and to characterize the transmission of arterial pressure across the AVM nidus. DVP measurements were carried out during elective AVM resection with isoflurane/nitrous oxide anesthesia with arterial carbon dioxide pressure of ≈ 30 mm Hg. The gradient between the right atrium and operative measurement site was noted. Pre-excision feeding mean arterial pressure and DVP were measured with a 26-gauge needle simultaneously with systemic mean arterial pressure and central venous pressure (CVP). DVP was tested with systemic mean arterial pressure increased to ≈ 20 mm Hg with phenylephrine or CVP increased with a Valsalva maneuver. Finally, preresection and postresection DVP values were compared. Relative to the site of measurement, DVP was 7 ± 5 mm Hg at a CVP of −4 ± 5 mm Hg (n = 45). There was no influence of presentation, presence of deep venous drainage, size, location, or prior embolization on DVP. In 19 patients, DVP decreased (8 ± 4 to 5 ± 3; P < 0.05) whereas CVP increased from pre- to postresection (−4 ± 5 to −2 ± 5; P < 0.05). For the phenylephrine challenge (n = 11), there was no difference (P = 0.84) between the ΔDVP (2 ± 1 mm Hg) and the ΔCVP (2 ± 3 mm Hg). For the Valsalva maneuver challenge (n = 7), however, ΔCVP (8 ± 4 mm Hg) was greater (P < 0.02) than ΔDVP (3 ± 2 mm Hg). Feeding mean arterial pressure and DVP were positively correlated (y = 0.2x + 2.4; r = 0.59; n = 14; P < 0.05) without any apparent influence of angiographic venous stenosis. Nevertheless, transnidal pressure drop or net cerebral perfusion pressure gradient (i.e., the lowest possible perfusion pressure to which normal adjacent circulatory beds might be exposed) was inversely correlated with AVM size (y = −6.1x + 52.3; r = 0.68; n = 14; P < 0.01). Clinically relevant changes in systemic mean arterial pressure and CVP affect DVP more as a venous than as an arterial structure. Most importantly, higher feeding mean arterial pressure is associated with higher DVP, but notwithstanding, a lower transnidal pressure gradient is present in larger AVMs. A lower transnidal pressure gradient, which may be associated with certain postoperative hemodynamic complications when transmitted to adjacent capillary beds, also may protect against spontaneous intranidal vessel rupture.