Intracardiac echocardiographic imaging of the left ventricle from the right ventricle: quantitative experimental evaluation.

PURPOSE

Our purpose was to demonstrate that intracardiac ultrasound imaging from a transducer placed in the right ventricle can be used to quantitatively image the left ventricle in a swine model.

BACKGROUND

The left ventricles and right ventricles of dogs and human beings have been studied with intracardiac echocardiography. Usually intracardiac echocardiography has been performed with the ultrasound catheter in the chamber being studied because of limited depth of field. Thus left ventricular imaging required that the ultrasound catheter be placed intra-arterially and manipulated into the left ventricle. The availability of lower frequency ultrasound catheters may allow left ventricular imaging from the right ventricle--a more clinically attractive approach.

METHODS

In 10 closed chest swine, a 10F, 10-MHz ultrasound catheter was placed into the right ventricle through an introducer sheath placed in the right internal jugular vein. Two-dimensional transthoracic echo images were obtained for comparison. Two protocols were used to image global left ventricular function and regional wall motion during pharmacologic challenge. In protocol 1 (n = 4) we evaluated global left ventricular performance in response to interventions: dobutamine, halothane (a myocardial depressant), nitroprusside, and volume loading. In protocol 2 (n = 6) we evaluated regional contraction abnormalities induced by coronary arterial balloon inflation and deflation (reperfusion) and dobutamine. At baseline and after each intervention, global function of the right ventricle and left ventricle was measured as cross-sectional end-diastolic area and end-systolic area, and regional contraction was evaluated as the percentage of left ventricular circumference with a wall motion abnormality. Intracardiac pressures and cardiac output were also measured for comparison. Left ventricular cross-sectional area ejection fractions (area EF) were calculated for both intracardiac and transthoracic echo images as (end-diastolic cross-sectional area - end-systolic cross-sectional area)/end-diastolic cross-sectional area.

RESULTS

The 10F, 10-MHz intracardiac ultrasound catheter successfully imaged the left ventricle from the right ventricle in all 10 swine. In protocol 1, dobutamine increased area EF from a baseline of 0.60 +/- 0.03 to 0.87 +/- 0.04 (P < .05). When dobutamine was added to the myocardial depressant halothane, left ventricular area EF increased from a baseline of 0.55 +/- 0.03 to 0.68 +/- 0.04. In protocol 2, coronary occlusion resulted in a detectable regional wall motion abnormality (circumferential percentage) of 23% +/- 3%. After reperfusion and during dobutamine stimulation, the wall abnormality decreased to 12% +/- 4%. Transthoracic echocardiography correlated well with these intracardiac findings.

CONCLUSIONS

The left ventricle can be quantitatively imaged from the right ventricle with the use of a 10F, 10-MHz intracardiac catheter in swine. This system can detect changes in global and regional left ventricular systolic function. This technique warrants evaluation in clinical applications.