New Discoveries Regarding the Limitations of Impedance Monitoring for Heart Failure Management

Background: Patients sustaining an acute myocardial infarction (AMI) frequently develop acute heart failure (AHF) during hospitalization. Treatment is initiated only after the appearance of overt signs of lung fluid overload. Ongoing monitoring of the status of lung fluid content (LFC) in AMI patients may enable the prediction of impending AHF and preemptive therapy, thus precluding AHF and improving outcomes. Aims: We sought to find out whether non-invasive lung impedance (LI) guided preemptive treatment of AMI patients improves clinical outcomes.Methods: LI was determined by using a new method based on detection of transverse propagation of electromagnetic energy through chest. Any increase in LFC results in LI decrease. Previously we have found that a decrease of 12-14% from normal LI value reflects the transition from interstitial to alveolar edema. In the present study we randomized 213 patients (2:1 ratio) admitted for their first AMI with no chronic heart failure (CHF) who expressed a O12% LI decrease to conventional therapy or LI-guided preemptive treatment. Results: 142 patients were treated conventionally (Gr1) and 71 preemptively according LI (Gr2). Groups were compatible with regard to clinical and laboratory parameters, (age: 61.3 6 14.1vs 59.9 6 11.5, LVEF: 45.9 6 12.4% vs 47.1 6 11.8%, CPKmax: 2078 6 1938 vs 1927 6 1622). In Gr1, AHF treatment was begun only at symptom onset. As a result, all patients developed some degree of AHF. In Gr2, preemptive treatment halted AHF development in 89% of patients. Hospital stay in Gr1patients was longer 1.4-fold (p!0.0001). Readmissions for cardiovascular causes within the first year after discharge was 1.5 times more common in Gr1 (p!0.01). During 6 years mean follow-up progression to CHF was 2-fold and mortality 2.8-fold higher in Gr1 (p! 0.01). Multivariate logistic regression analysis with age, LVEF and CPKmax as non dependent variables was performed. All differences between Gr1 and 2 remained significant. LI-guided therapy in Gr2 reduced progression to CHF during a 6-year period, OR50.37 [CI: 0.17-0.8, p50.01] and mortality OR50.34 [CI: 0.12-0.92, p! 0.0001]. Factors that prolonged hospital stay in both groups were age (F518.5), CPKmax (F510.7), LVEF (F59.6) while preemptive therapy reduced it (F515.8). Conclusions: LI-guided preemptive therapy halts progression to AHF in 89% of patients, and significantly reduces hospital stay, recurrent admissions, evolution of CHF and mortality.