Impedance Cardiography in the Evaluation of Left Ventricular Diastolic Dysfunction in Patients With Arterial Hypertension Study (IMPEDDANS)

BACKGROUND. Impedance cardiography (IC) is a complementary diagnostic test used in the study of arterial hypertension (AHT) and in the optimization of antihypertensive therapy. It is easy-to-execute, non-operator-dependent and cost-effective. It analyses and registers hemodynamic changes through the measurement of electrical resistance changes in the thorax and translates them graphically as impedance and electrocardiogram waveforms. IC has evolved in recent years, making it an attractive and economical tool, particularly in screening settings and there is extensive published literature on its usefulness. More widespread use of IC has been limited due to limitations of the studies, mostly cross-sectional, with small samples, recruiting hemodynamically stable patients and providing inconsistent estimates of accuracy and reproducibility in different settings.

AHT is responsible for high morbidity and mortality. In Portugal, according to PHYSA study, has overall prevalence of hypertension, in 2014, of 42.2% (44.4% in men, 40.2% in women). The progression of hypertensive heart disease involves myocardial fibrosis and changes in left ventricular geometry that precedes functional changes. Diastolic dysfunction is part of this continuum, and despite the growing recognition of its importance, it is generally undervalued because of the difficulty in its diagnosis and the absence of effective therapies. This reinforces the importance of finding alternative tests that provide important information for an initial assessment of diastolic function in hypertensive patients.

This study intends to define the importance and usefulness of IC in the evaluation of LV diastolic dysfunction in patients with AHT.

METHODS. Study Design. This is a validation study of a diagnostic method used in a new context, comparing it with the diagnostic method currently used for this effect in usual clinical practice. Its purpose is to determine the positive predictive value, negative predictive value, sensitivity and specificity of the presence of the D wave, the isovolumetric relaxation time, the systolic time ratio (STR) and thoracic fluid content (TFC) by IC, for the diagnosis of LV diastolic dysfunction (LVDD). To study the relationship between LV geometry, hemodynamic profile, diastolic dysfunction and its degree (confirmed by echocardiography) in hypertensive patients with diastolic dysfunction. We chose to perform a concordance study between IC and echocardiography, the validated , non-invasive test used for the clinical diagnosis of LVDD as well as for the characterization of hypertensive cardiopathy.

To calculate the sample size we considered the primary endpoint (concordance of the diagnosis of diastolic dysfunction between IC and echocardiography). Thus, considering a hypothesized positive predictive value of 70 ± 5% of the parameters obtained by IC, 77 individuals are estimated to be able to verify the expected positive predictive value with 95% confidence. Since the prevalence of diastolic dysfunction in patients with AHT estimated to be approximately 50% in most studies, the sample size is doubled for 154 hypertensive patients.