Update of implantable cardioverter/defibrillator and cardiac resynchronization therapy in heart failure

The effect of comorbidity on the competing risk of sudden and nonsudden death in an ambulatory heart failure population

BACKGROUND

Sudden death (SD) and non-sudden cardiac death are responsible for the majority of deaths in patients with heart failure. We sought to identify the influence of comorbid illness (Charlson Comorbidity Index [CCI]) on competing modes of death in heart failure.

METHODS

A retrospective analysis of 824 patients followed in a tertiary care heart failure clinic was performed. We analyzed the cumulative incidence of sudden and nonsudden death. Competing risk regression was used to examine the association between medical comorbidities and mode of death. The outcomes of interest were overall mortality, SD, SD and/or appropriate implantable cardioverter-defibrillator therapy (ICD), and non-SD.

RESULTS

Mean age of the study population was 64.1 ± 14.7 years, 68.6% were male, and mean ejection fraction was 32.8% ± 13.5%. Over a mean follow-up of 4.4 years, 229 patients (27.8%) died. SD accounted for 33 deaths (14.4%), whereas SD/appropriate ICD therapy occurred in 56 patients (24.5%). The risk of non-SD and total mortality increased (P < .0001) as the CCI increased, whereas the risk of SD decreased (P = .03). The cumulative incidence of SD, SD and/or ventricular tachycardia/fibrillation, and non-SD at 5 years was 5.6%, 9.1%, and 27.8%, respectively. In multivariate competing risk analysis, advancing age, New York Heart Association class, and a CCI >4 were significantly associated with non-SD.

CONCLUSION

Patients with heart failure with significant comorbidities are much more likely to sustain non-SD. These findings may have implications in optimal selection of patients with heart failure for interventions such as prophylactic ICD therapy.

Feasibility of using an implantable system to measure thoracic congestion in an ambulatory chronic heart failure canine model

BACKGROUND

Noninvasive measures of impedance reflect alterations in thoracic fluid and pulmonary edema in acute animal and human studies.

MATERIALS AND METHODS

We evaluated the feasibility of using an implantable impedance measuring device and cardiac lead system to monitor intrathoracic congestion in a pacing-induced heart failure canine model. Three devices were implanted in each of five dogs: a modified pacemaker to measure impedance from a defibrillation lead implanted in the right ventricle; an implantable hemodynamic monitoring device to measure left ventricular end diastolic pressure (LVEDP) and a second pacemaker to deliver rapid (240 pulses per minute) ventricular pacing to induce heart failure.

RESULTS

All five dogs developed severe heart failure after 3-4 weeks of rapid pacing and recovered following pacing termination. The LVEDP increased and impedance decreased during pacing-induced heart failure and recovered after pacing cessation. At the end of pacing, there was a mean impedance reduction of 10.6 +/- 8.3% and a mean LVEDP increase of 18.1 +/- 4.5 mmHg compared to baseline. The impedance and LVEDP were inversely correlated (r =-0.41 to -0.85, all P < 0.05).

CONCLUSIONS

In the canine model, measurement of chronic intrathoracic impedance with an implantable system effectively revealed changes in thoracic congestion due to heart failure reflected by LVEDP. These data suggest that implantable device-based impedance measurement merits further investigation as a tool to monitor the fluid status of heart failure patients.