Transcatheter coronary artery diagnostic techniques including impedance-catheter and impedance-guidewire measurement of absolute coronary blood flow.

Interventional cardiology requires precise assessment of coronary anatomy and physiology. Unfortunately, however, important interventional decisions are frequently made on the basis of arteriographic data alone. Increasing evidence suggests that visual interpretation of coronary arteriographic studies is irreproducible, inaccurate, and poorly predictive of coronary physiology. Moreover, arteriography is of little value in assessing endothelial ulceration and mural thrombus, which are important pathophysiologic features of unstable angina and acute myocardial infarction. In response to these limitations, several diagnostic transcatheter techniques have been developed that allow more complete assessment of coronary physiology and function. These include fiberoptic angioscopy, reflection spectroscopy (which can combine automated laser therapy with diagnosis), ultrasonic catheterization, and translesional gradient determination. Doppler catheterization permits the assessment of overall coronary flow reserve with the aid of induced hyperemia, whereas subselective digital radiography allows the evaluation of regional coronary flow reserve. The coronary flow reserve, however, may be falsely lowered immediately after balloon dilation, because of endothelial injury, repeated ischemia, or the administration of vasoactive drugs. To circumvent this problem, we have developed impedance-catheter and impedance-guidewire systems that, by applying impedance technology and the principles of indicator dilution, are capable of measuring absolute coronary blood flow. For a flow indicator, we use 0.5 mL of glucose solution (D5W), which has little effect on intrinsic blood flow. The validity of this approach has been demonstrated in experimental and clinical studies. The impedance guidewire is less obstructive than the catheter system, so it probably will become the method with clinical application.