High-density bubble echocardiography for patent foramen ovale assessment: sensitivity and relationship with invasively measured shunt severity and atrial septum morphology

Background Transthoracic contrast echocardiography (cTTE) is a first-line method for patent foramen ovale assessment (PFO), but its sensitivity is reported as low and inconsistent. We aimed to investigate the sensitivity of high-density bubble study cTTE for PFO detection, and the relationship between left-heart contrast opacification grade, invasively measured shunt severity and atrial septum/PFO morphology. Methods Fifty-five consecutive patients with proven PFO on contrast transoesophageal echocardiography (cTOE) underwent contrast transthoracic echocardiography (cTTE) and invasive right-to-left shunt severity measurement. Echocardiographic shunt severity was classified according to the degree of left atrial (cTOE) or left atrial/ventricular (cTTE) opacification as grade 0: no bubbles; grade 1: mild; grade 2: moderate; grade 3: significant opacification. The thermodilution method was used for the right-to-left heart shunt measurement. Results For PFO detection, the sensitivity of rest + Valsalva cTOE was 100%, but rest cTOE vs rest + Valsalva cTOE was 77.3%. For transthoracic studies, the sensitivity of rest + Valsalva cTTE was 98.2%, Valsalva cTTE 97.6%, and rest cTTE 83.6% vs rest + Valsalva cTOE. No relationship was found between rest or Valsalva cTTE and cTOE left-heart bubble opacification grade and invasively measured right-to-left shunt < 10%, 10–19%, or ≥ 20% (p = 0.10–0.26). A moderate association only was revealed between rest + Valsalva cTOE opacification grade and < 10% and ≥ 10% right-to-left shunt (p = 0.024, Cramér's coefficient = 0.368). No relationship was also found between left-heart opacification grade and the presence of an atrial septal aneurysm, Eustachian valve/Chiari's network, or PFO channel width and length (p = 0.45–0.77). Rest cTTE demonstrated equal contrast opacification grade in 56% and higher in 40% vs rest cTOE. Valsalva cTTE showed equal contrast opacification grade in 29% and higher in 46% of studies vs Valsalva cTOE. Conclusions In bubble studies using high-density contrast, cTOE and cTTE with Valsalva, but not rest studies, are highly sensitive for PFO assessment. There is no clinically relevant relationship between the left-heart bubble opacification grade and invasively measured right-to-left shunt severity or atrial septum morphology. The left-heart opacification degree is equal to or higher in cTTE than in cTOE, especially in rest studies.