IPF is a progressive fibrosing interstitial pneumonia that increases in prevalence with advanced age [1]. The median age for the diagnosis of IPF is about 70 years [23, 24]. Some patients with IPF require hospitalization for HF during the clinical course of the disease [3]. We classified the patients with HF into 3 groups, those with HFpEF, HFrEF, or HFPH, and compared the groups. HFpEF was the most frequent type of HF. The patients with HFpEF showed the most favorable survival, but also recurred at the highest rate.
Approximately 50% of patients with HF have been reported to have a normal or nearly normal LVEF [6-8]. Old age, female sex, hypertension, high body mass index, smoking, and diabetes were reported to be risk factors for HFpEF [9, 25]. Patients with HFpEFalso can have a respiratory comorbidity such as chronic obstructive pulmonary disease [26, 27], which leads to increased risk of mortality [27].
Although only a few studies have reported on the relationship between interstitial lung disease and left HF, it has been suggested that some patients with IPF have HFpEF, or diastolic dysfunction [28-30]. Our study focused on LV function in patients with IPF who were hospitalized because of HF. We found that some patients with IPF had HFpEF when they were hospitalized.
We defined patients with HFPH as those patients with an RVSP ≥ 50 mm Hg on echocardiography. The patients with HFPH showed the highest mortality rate. We could not clarify whether or not the PH we identified was a new condition that began at the time of hospitalization. Some patients with IPF and existing PH also need hospitalization. In those cases, the hospitalization may be associated with the existing PH and related right HF [10]. Patients who have IPF and chronic, stable PH have a poor prognosis [31, 32]. Although several clinical trials for patients with IPF and PH have been conducted, there is no effective treatment [33-38]. This might account for the poor survival of our hospitalized study patients with acute HF and PH coinciding with IPF.
A preventative treatment against the acute worsening of HFpEF remains unknown. Myocardial fibrosis is reported to be important in the pathophysiology of HFpEF [39]. Transforming growth factor beta (TGF-β) has a key role in both the development of myocardial fibrosis and IPF [40, 41]. Based on the hypothesis that HFpEF and IPF share common molecular pathways, antifibrotic agents are candidates for the treatment of patients with HFpEF and also for the prevention of acute worsening. Actually, pirfenidone, which was approved for patients with IPF, might be effective for patients with HFpEF, given that pirfenidone attenuates the profibrotic effects of TGF-β in human lung fibroblasts and inhibits cardiac fibrosis in animal models [42-46].A phase II trial of pirfenidone for patients with HFpEF is now ongoing [47].
Nintedanib is a tyrosine kinase inhibitor that has also been approved for the treatment of IPF [48, 49]. Nintedanib has been shown to inhibit TGF-β-induced transformation of fibroblasts to myofibroblasts [50]. However, the effect of nintedanib on cardiac fibrosis has not been proven.
Our study has several limitations. First, the study was conducted in a retrospective fashion. Second, the study was performed at a single center with a small number of patients. Third, both the underdiagnosis and overdiagnosis of HF might have occurred, although we diagnosed HF based on the criteria proposed in the Framingham study [14]. IPF and HF share a number of common signs/symptoms such as cough, dyspnea, fatigue, and reduced exercise tolerance in patients with chronic stable disease [51-53]. In the acute setting, an accurate diagnosis is even more difficult to obtain. Fourth, PH was diagnosed by echocardiography, although right heart catheterization (RHC) is required for the definitive diagnosis of PH [22]. However, performing RHC for all patients with suspected PH who are hospitalized is unpractical because it is an invasive and inconvenient procedure. Fifth, patients with HFpEF or HFrEF associated with PH were classified as a single group of patients with HF due to PH [54]. Further studies are needed that focus on hospitalized patients with IPF and PH in order to determine an accurate classification. And sixth, the LV function and RVSP of patients before hospitalization were unknown. We could not clarify if the HF and PH at hospitalization were due to the worsening of chronic HF and PH or the new onset of these conditions. A prospective study is needed to clarify the times of onset.
In conclusion, HFpEF is the most common type of HF that requires nonelective hospitalization in patients with IPF. Patients with HFpEF survived longer than patients with HFrEF and HFPH.