Clinical implications of pulmonary shunting on contrast echocardiography

Pulmonary right-to-left shunting can be encountered using transthoracic contrast echocardiography (TTCE) with agitated saline. Diseases associated with prevalence of pulmonary shunting on saline TTCE include hereditary haemorrhagic telangiectasia (HHT), hepatopulmonary syndrome and some congenital heart defects after partial or complete cavopulmonary anastomosis. Furthermore, small pulmonary shunts on saline TTCE are also documented in a proportion of healthy individuals. Pulmonary shunting carries the risk for severe neurological complications due to paradoxical embolisation. In HHT, additional chest CT is recommended in case of any pulmonary shunt detected on saline TTCE, in order to evaluate the feasibility for transcatheter embolotherapy of pulmonary arteriovenous malformations (PAVMs). Furthermore, antibiotic prophylaxis is advised in case of any pulmonary shunt on saline TTCE to prevent brain abscesses after procedures with risk of bacteremia. The present thesis provides an overview of important aspects of pulmonary shunting and its detection using saline TTCE. Furthermore, advances in understanding the clinical implications of different pulmonary shunt grades on saline TTCE are described. It appears that small pulmonary shunts on saline TTCE lack any clinical implication, as these shunts cannot be used as a diagnostic criterion for HHT, are not associated with an increased risk for neurological complications and represent PAVMs too small for subsequent endovascular treatment. This implies that additional chest CT could be safely withheld in all persons with only a small pulmonary shunt on saline TTCE and sets the stage for further discussion about the need for antibiotic prophylaxis in these subjects. Besides further optimization of the current screening algorithm for the detection of PAVMs in HHT, these observations can be of additional clinical importance in other diseases associated with pulmonary shunting and in those healthy individuals with a documented small pulmonary shunt on saline TTCE.