A New Non-Invasive Approach for Accessing Pulmonary Arterial Stiffness in Patients with Pulmonary Hypertension

Pulmonary hypertensionPHis a disease affecting approximatelyof the general population that is characterized by abnormally elevated mean pulmonary artery pressuremPAPand pulmonary vascular resistancePVRIf left untreatedPH can ultimately lead to right heart failure and deathCurrent diagnostic approaches utilize invasive right heart catheterizationRHCto measure mPAP and PVREarly detection of PH leads to improved prognosisAn increase in pulmonary arterial stiffness is the earliest physiological manifestation of PH and precedes an increase in mPAPPA impedance describes opposition to blood flow and consists of pulsatile and resistive componentsIt accurately quantifies PA stiffness under both normal and pathological conditionsincluding the early stages of PHPA impedance is not usually measured in clinical practice because it requires simultaneous invasive pressure and flow measurementsA reliable non invasive procedure to assess the stiffness of pulmonary arteries that can be used in a large group of patients would be extremely useful in early diagnosis of PH and could improve clinical outcomesA novelnon invasive technique is proposed based on a transfer function between velocities measured by standard phase contrast MRI that measures a quantity related to PA stiffnessThe compliance of the PA causes frequency dependent changes in an input velocity waveform as it travels through the artery thereby producing an output velocity waveformThe frequency dependent relationship between the input and output velocity waveforms are described by a transfer functioncalled the velocity transfer functionVTFwhich is the ratio of the frequency spectra of input and output waveformsResults from a study ofconsecutively enrolled patients recently published in the Journal of the American Heart Association demonstrate that the VTF has a strong association with invasive PA impedance independent of elevation in pulmonary capillary wedge pressure and accurately assesses PA stiffness and elevated PVRThis study demonstrated that VTF is an accurate and reliable non invasive surrogate of PA impedance and thuscan potentially be used as a screening tool for pre capillary pulmonary hypertension before more expensive or invasive tests are consideredDevelopment and validation of a commercial quality software package is proposed that inputs phasecontrast MRI data and calculates the VTF with the ultimate goal of obtaining Food and Drug AdministrationFDAapprovalWe do not anticipate that the VTF will totally replace a RHCbut it could reduce the number of RHCs by allowing patients to be screened for PH with more accuracy earlier in the diagnostic process and to be followed non invasively over time Current procedures for diagnosing pulmonary hypertensionPHare invasive and only detect the disease in later stagesA software package will be developed and validated based on a novelnoninvasive technique that can evaluate the pulmonary arteryPAfrom standard phase contrast MRIOutcomes for PH patients could potentially be improved by earlier diagnosiswhere therapies are more effectiveand fewer invasive procedures