Transthoracic contrast echocardiography in the detection of patent foramen ovale

A patent foramen ovale (PFO) is a common clinical finding and is becoming increasingly implicated in several important pathophysiological conditions, including cryptogenic embolic stroke, migraine with aura, decompression sickness and, more rarely, acute myocardial infarction [1]. Echocardiographic techniques are the principal means for diagnosis and assessment of a PFO [2]. The development of transthoracic echocardiography (TTE) with harmonic imaging coupled with the use of contrast and provocation testing has potentially enhanced our ability to detect a PFO transthoracically.

Methods

A total of 20 patients with an unexplained embolic event were recruited. We compared four routes of contrast delivery (upper extremity vein in a dependent position, upper extremity vein in an elevated position, right femoral vein and lower extremity vein) with provocation manoeuvres on the detection of PFO using both TTE and transoesophageal echocardiography (TOE). The route of contrast delivery was performed in a random fashion. Studies were interpreted in real time by an echocardiographer in an unblinded manner as in real-life clinical practice. All studies were digitally recorded and later reviewed independently by a second BSE-accredited echocardiographer blinded to the sequence and site of contrast injections.

Results

The mean age of the 20 patients was 24 ± 10.7 years and 12 (60%) were male. All patients were in sinus rhythm. Six patients (30%) were exsmokers and four (20%) current smokers. Two patients were on treatment for hypertension and five (25%) patients had hyperlipidaemia (total cholesterol >5 mmol/l). One patient suffered with type 1 diabetes mellitus. The prevalence of PFO detected by the TTE approach combined with a provocation manoeuvre was 50% (10/20). The prevalence in divers was 100% (5/5) and 38% (5/13) in patients with a cryptogenic stroke/TIA. TOE only detected 5/20 (25%) PFOs. All PFOs detected by TOE were detected by TTE. Valsalva improved the detection rate for all routes of contrast delivery except i.v. access at the ankle. The highest detection rates were seen with contrast injection in the elevated arm or via the right femoral venous route (10/20). Agreement between reviewers was excellent (P < 0.01). All non-agreement observed between TTE and TOE occurred when TTE reported a positive result and TOE a negative result. In 9/10 (90%) cases the clearest image was using TTE, with 7/9 (78%) following a provocation manoeuvre. Left ventricular opacification was most marked during femoral vein delivery of the contrast agent coupled with the valsalva manoeuvre and TTE.

Conclusion

TTE with harmonic imaging and femoral vein delivery of contrast should be regarded as the gold standard for the echocardiographic detection of PFO. Maximising the contrast load by use of the large antecubital vein and arm elevation improves detection if arm injection is used.