Congestive heart failure (CHF) is one of the most challenging diseases in terms of health care demand and mortality, in the western world. Despite major breakthroughs in the fields of diagnosis and treatment over the three last decades, the management of CHF still remains challenging.
CHF is defined as inability of the heart to supply sufficient blood flow to meet the needs of the body. This definition however, may be an oversimplification of a complex pathophysiological process since patients with overt CHF may have normal, or even supernormal cardiac output at the expense of increased filling pressures, which subsequently leads to the development of post capillary pulmonary hypertension (PH). In the presence of advanced CHF, clinical signs and symptoms are obvious at rest. However, the majority of affected individuals do not experience any discomfort at rest and may demonstrate normal findings when assessed. Small increases in systemic blood pressure and or venous return, caused by activity may result in severe elevation of filling pressures if left ventricular compliance is significantly decreased. This example highlights the need to perform cardiac investigations during stress to provoke symptoms. Increased pulmonary vascular resistance (PVR), commonly found in pre-capillary PH, is a condition that shares many symptoms with CHF, and is also associated with poor prognosis. Even though the disease is located within the lung vessels, it is highly important and challenging task differentiating pre- and post-capillary PH. Since treatment differs considerably and may be detrimental in case of misdiagnosis, additional sensitive and reliable screening methods are crucial to aid in differentiation.
Methods: Out of the four studies included in this thesis, three were conducted solely at Norrland’s University Hospital, while patients in the third study were recruited and examined at Uppsala Akademiska Hospital. All included patients had idiopathic dyspnea and were admitted for right heart catheterization (RHC), which is gold standard with regards to hemodynamics. Echocardiographic examinations were performed simultaneously with RHC, except in the Uppsala study, wherein echocardiography were performed within 3 days to the RHC.
Echo-Doppler derived pulmonary artery acceleration time (PAcT) is an easily assessed parameter, indicating elevated pulmonary artery systolic pressure (PASP) and pulmonary artery resistance (PVR). PAcT was tested as a screening method for identification and differentiation of pre and post- capillary PH in a cohort of 56 patients (study 1).
The ability to calculate PVR non-invasively, using novel echocardiographic measurements, was made by replacing the invasive pressure and flow components that constitutes the foundation of the PVR = (mean pulmonary artery pressure – Pulmonary capillary wedge pressure (PCWP)) /cardiac output), with novel echocardiographic measurements. PVR = mPAP-Chemla – Left atrial strain rate during atrial systole (LASRa) / Cardiac Output-Echo (study 2).
Invasively measured left ventricular filling pressure in response to passive leg lifting, and its ability to predict pathological increase in left ventricular filling pressures during supine bicycling, was tested in a population of 85 patients with normal left ventricular ejection fraction (LVEF) and suspicion of CHF based on NT-proBNP levels alone were investigated (Study 3).
Finally, an evaluation of standard and novel Doppler echocardiographic parameters, potentially useful in identifying patients who may develop increased filling pressures during passive leg lifting (PLL), was carried out (study 4).
Results:
Study 1: PAcT correlated negatively with pulmonary artery systolic pressure (PASP) (r = -0.60, p < 0.001) and PVR (r = -0.57, p < 0.001). PAcT of <90 ms had a sensitivity of 84% and a specificity of 85% in identifying patients with PVR ≥ 3.0 WU. Regardless of normal or elevated left sided filling pressures, PAcT differed significantly in patients with normal, compared to those with elevated levels of, PVR (p < 0.01). A significant difference was also found on comparison of the PAcT/PASP ratio (p < 0.01), with a lower ratio among patients with PVR ≥ 3.0. WU.
Study 2: We prospectively used Doppler and 2D echocardiography in 46 patients with sinus rhythm which revealed that left atrial strain rate during atrial systole (LASRa) had the highest significant positive correlation with PCWP (r2 = 0.65, P < 0.001). By adopting a linear line of best-fit, LASRa may therefore be substituted for PCWP. Subsequently, LASRa was substituted into the PVR equation. This novel echocardiographically derived PVR calculation, significantly correlated with RHC generated PVR values (r2 = 0.69, P < 0.001) and minor drift (+0.1WU) when assessed by Bland Altman analysis.
Study 3: Only 22% (11/51) of patients with elevated NT-proBNP had PCWP above normal levels at rest. However, in response to PLL, 47% of patients developed elevated PCWP, and the majority of this 47% subsequently developed pathological pressure levels while performing supine cycling exercise. Thus, the likelihood of developing high LVFPs during exercise could be determined by PLL, with a sensitivity and specificity of 90%.
Study 4: At rest, left atrial volume indexed to body mass index (BMI) (LAVI) and mitral deceleration time (DT) were independently related to PCWP during PLL. However, during PLL univariate regression analysis revealed LASRa (β = -0.77, P <0,001) and E/LVSRe (β = 0.47, P < 0,021) most related to PCWPPLL. Multiple regression analysis fortified LASRa and E/LVSRe as relevant independent parameters useful in the assessment of filling pressure during PLL.
Conclusion: A PAcT < 90ms is strongly suggestive of increased PVR (>3.0 WU). Based on study 1, there is clear evidence suggesting that these findings apply irrespective of LVFPs. PAcT can potentially serve as a rapid screening tool for estimation of PVR, however, is not useful if the exact level of PVR is required. In this case, an established PVR calculation method is preferred, and could be performed with higher precision by inclusion of echocardiography derived LASRa as a surrogate measure of PCWP. Insufficient LV compliance results in the inability to cope with increased cardiac preload. Nt-proBNP is secreted when the myocardium is stretched, however only a small portion of patients within the CHF group (study 3) had a high PCWP at rest. Nearly half of the study population with elevated NT-proBNP showed increased PCWP during PLL, which is indicative of underlying ventricular stiffness. By performing this preload increasing maneuver, patients predisposed to developing high filling pressure during supine cycling could be identified with high sensitivity and specificity. Echocardiography, in comparison with RHC, is more accessible, safer and requires less resources and time, thus is an appealing option in the quest to identify additional, non-invasive methods reflective of invasive pressures, which could be useful in the assessment of filling pressure during different loading conditions. LAVI at rest, LASRa and E/LVSRe during PLL, proved independently related to PCWP during PLL.