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Abstract and Introduction
Abstract
Background Cardiac and systemic hemodynamics have been historically in the domain of invasive cardiology, but recent advances in real-time 3-Dimensional echocardiography (RT3D echo) provide a reliable measurement of ventricular volumes, allowing to measure a set of hemodynamic parameters previously difficult or impossible to obtain with standard 2D echo.
Aim To assess the feasibility of a comprehensive hemodynamic study with RT-3D echo.
Methods We enrolled 136 patients referred for routine echocardiography: 44 normal (N), 57 hypertensive (HYP), and 35 systolic heart failure patients (HF). All patients underwent standard 2D echo examination followed by RT3D echo examination, including measurement of left ventricular (LV) end-diastolic and end-systolic volumes and derived assessment of LV elastance (an index of LV contractility), arterial elastance (characterizing the distal impedance of the arterial system downstream of the aortic valve); ventricular-arterial coupling (a central determinant of net cardiovascular performance); systemic vascular resistances. Blood pressure was derived from cuff sphygmomanometer and heart rate from ECG.
Results A complete 2D echo was performed in all 136 patients. 3D echo examination was obtained in 130 patients (feasibility = 95 %). Standard 2D echo examination was completed in 14.8 ± 2.2 min. Acquisition of 3D images required an average time of 5 ± 0.9 min (range 3.5–7.5 min) and image analysis was completed in 10.1 ± 2.8 min (range 6–12 min) per patient. Compared to N and HYP, HF patients showed reduced LV elastance (1.7 ± 1.5 mmHg mL m, p <0.001 vs N = 3.8 ± 1.3 and HYP = 3.8 ± 1.3) and ventricular-arterial coupling (0.6 ± 0.5, p < 0.01 vs N = 1.4 ± 0.4 and HYP = 1.2 ± 0.4). Systemic vascular resistances were highest in HYP (2736 ± 720, p < .01 vs N = 1980 ± 432 and vs HF = 1855 ± 636 dyne*s/cm). The LV elastance was related to EF (r = 0.73, p < 0.01) and arterial pressure was moderately related to vascular elastance (r = 0.54, p < 0.01). The ventricular-arterial coupling was unrelated to systemic vascular resistances (r = −0.04, p NS).
Conclusion RT-3D echo allows a non invasive, comprehensive assessment of cardiac and systemic hemodynamics, offering insight access to key variables – such as increased systemic vascular resistances in hypertensives and reduced ventricular-arterial coupling in heart failure patients.
Introduction
LV function, ventricular volumes, and ejection fraction are routinely assessed by standard 2D echo for early detection of cardiac disease, to monitor disease progression and to assess response to treatment. Standard echocardiographic evaluation of hemodynamic parameters shows an acceptable correlation with invasive measurements in population studies. However, in the individual patient, the dispersion of values may be so wide to limit clinical applications, mostly due to intra- and inter-observer variability of volumes measurements. RT-3D improves accuracy of non-invasive evaluation of cardiac volumes limiting data scatter and provides reliable clinical guidance. Moreover RT-3D echo, by accurate assessment of stroke volume (SV), allows to derive a set of hemodynamic measures usually difficult or impossible to obtain with 2D echo, such as LV elastance, arterial elastance, ventricular-arterial coupling and systemic vascular resistances.
The underlying idea of the present study was to take advantage of the superiority of 3D over 2D echocardiography in assessing LV volumes to derive more accurate non invasive estimates of cardiac-vascular function.
The purpose of this study was to evaluate the feasibility and time cost of RT-3D echo, as compared to standard 2D echo, in the setting of a primary care echocardiography laboratory.
We also evaluated RT3D derived cardiac and vascular hemodynamics in hypertensive and heart failure patients. In fact, RT3D-derived parameters such as left ventricular elastance or systemic vascular resistances reflect the complex interactions between the heart and its internal and external loads and are of emerging importance in the assessment and management of hypertension and heart failure.
Study Population
The study has been conducted in 3 different primary care cardiology outpatients clinic (Echocardiography Laboratories of Savona, of Lucca, and of Barga cardiology services). All exams were performed by the same cardiologist-echocardiographer who performed both 2D and 3D echo examinations. To minimize variability the same observed, acquired and analyzed all studies. The observer had undergone a dedicated 9 month training on 3-D and the variability observed in a consecutive set of 10 studies was consistently < 10 % for LV volumes. We initially considered 400 patients, referred for clinically driven Echo evaluation between May 2009 and June 2011. Sixty patients denied the consent to enter the 3D part of the study, 50 had technically difficult 2D-Echo examination; 154 had exclusion criteria conditions (such as previous myocardial infarction, valvular heart disease or age below 40 y). One hundred and thirty six patients were eventually included in the study. They complied with the inclusion criteria:
Sinus Rhythm;
Willingness to enter the study;
Technically good 2D echo study;
Clinical-echocardiographic diagnosis of no structural heart disease (N, with SBP ≤ 139 mmHg, diastolic blood pressure ≤ 85 mmHg, and a BMI ≤ 30 Kg/m2), free from major coronary risk factors, including diabetes, hypercholesterolemia, and cigarette smoking;
Clinical-echocardiographic diagnosis of essential hypertension (HYP), previously made according to standard criteria: history of long standing high blood pressure, under active treatment with ACE-inhibitors (68 %), and/or diuretics (84 %), and/or ARBs (36 %), and/or Ca-channel blockers (25 %) with EF > 50 %;
Clinical-echocardiographic diagnosis of heart failure (HF): history of dyspnea on effort, under active treatment with ACE-inhibitors (86 %), and/or diuretics (78 %), and/or ARBs (28 %), and/or β-blockers (68 %), with EF < 40 %.
Study Protocol
Following standard 2D echo examination, patients underwent RT-3D echo with measurement of raw data of LV EDV and ESV and derived assessment of: LV elastance (an index of LV contractility); arterial elastance (AE) (characterizing the distal impedance of the arterial system downstream of the aortic valve); ventricular-arterial coupling (a central determinant of net cardiovascular performance); systemic vascular resistances (SVR). Blood pressure was derived from cuff sphygmomanometer and heart rate from 1- lead ECG (on echo monitor). The medical records of all included patients were reviewed in detail by one investigator to identify N, HYP and HF patients. For all patients, age, cuff blood pressure, height, weight, body mass index (BMI) and body surface area (BSA) were calculated and recorded.
Mean arterial pressure (MAP) was calculated as diastolic blood pressure + (systolic blood pressure - diastolic blood pressure/3). Mitral regurgitation and pulmonary arterial pressure were estimated from standard 2D echo. Forty four patients with no overt cardiac disease, a SBP ≤ 139 mmHg, and a BMI ≤ 30 Kg/m2, constituted the N group. Fifty seven subjects with hypertension but no HF constituted the HTN group. Thirty five patients with a clinical diagnosis of heart failure and EF below 40 % constituted the systolic HF group.
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