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CLINICAL STUDIES

Transthoracic echocardiography using second harmonic imaging

Diagnostic alternative to transesophageal echocardiography for the detection of atrial right to left shunt in patients with cerebral embolic events

Harald P. Kühl, MD^a, Rainer Hoffmann, MD^a, Marc W. Merx, MD^a, Andreas Franke, MD^a, Christof Klötzsch, MD^*, Wolfgang Lepper, MD^a, Thorsten Reineke, BSc, Johannes Noth, MD^* and Peter Hanrath, MD, FACC^a

^a Medical Clinic I, University Hospital, Aachen, Germany
^* Department of Neurology, University Hospital, Aachen, Germany
Institute of Biometry, University Hospital, Aachen, Germany

Manuscript received January 20, 1999; revised manuscript received June 14, 1999, accepted August 5, 1999.

Reprint requests and correspondence: Dr. Harald P. Kühl, Medizinische Klinik I, Universitätsklinikum der RWTH, Pauwelstrasse 30, 52057 Aachen, Germany
hkue{at}pcserver.mkl.rwth-aachen.de

OBJECTIVES

We sought to evaluate whether transthoracic contrast echocardiography using second harmonic imaging (SHI) is a diagnostic alternative to transesophageal contrast echocardiography (TEE) for the detection of atrial right to left shunt.

BACKGROUND

Paradoxic embolism is considered to be the major cause of cerebral ischemic events in young patients. Contrast echocardiography using TEE has proven to be superior to transthoracic echocardiography (TTE) for the detection of atrial shunting; SHI is a new imaging modality that enhances the visualization of echocardiographic contrast agents.

METHODS

We evaluated 111 patients with an ischemic cerebral embolic event for the presence of atrial right to left shunt using an intravenous (IV) contrast agent in combination with three different echocardiographic imaging modalities: 1) TTE using fundamental imaging (FI); 2) TTE using SHI; and 3) TEE. The severity of atrial shunting and the duration of contrast visibility within the left heart chambers were evaluated for each imaging modality. Image quality was assessed separately for each modality by semiquantitative scoring (0 = poor to 3 = excellent). Presence of atrial right to left shunt was defined as detection of contrast bubbles in the left atrium within the first three cardiac cycles after contrast appearance in the right atrium either spontaneously or after the Valsalva maneuver.

RESULTS

A total of 57 patients showed evidence of atrial right to left shunt with either imaging modality. Fifty-one studies were positive with TEE, 52 studies were positive with SHI, and 32 were positive with FI (p < 0.001 for FI vs. SHI and TEE). The severity of contrast passage was significantly larger using SHI (61.6 ± 80.2 bubbles) compared to FI (53.7 ± 69.6 bubbles; p < 0.005 vs. SHI) but was not different compared to TEE (43.9 ± 54.3 bubbles; p = NS vs. SHI). The duration of contrast visibility was significantly longer for SHI (17.4 ± 12.4 s) compared to FI (13.1 ± 9.7 s; p < 0.001) and TEE (11.9 ± 9.6 s; p < 0.02). Mean image quality improved significantly from FI (1.5 ± 0.8) to SHI (2.0 ± 0.8; p < 0.001 vs. FI) and TEE (2.5 ± 0.7; p < 0.001 vs. SHI).

CONCLUSIONS

In combination with IV contrast injections, TEE and SHI have a comparable yield for the detection of atrial right to left shunt. Both modalities may miss patients with atrial shunting. In young patients with an unexplained cerebrovascular event and no clinical evidence of cardiac disease, a positive SHI study may obviate the need to perform a TEE study to search for cardiac sources of emboli.

Abbreviations and Acronyms   ASD = atrial septal defect   CE = contrast echocardiography   CT = computed tomography   ECG = electrocardiogram   FI = fundamental imaging   IV = intravenous   LV = left ventricular   MRI = magnetic resonance imaging   PFO = patent foramen ovale   SHI = second harmonic imaging   TEE = transesophageal echocardiography   TTE = transthoracic echocardiography

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