Ventilatory gas exchange and early response to cardiac resynchronization therapy

Abstract

Background: Cardiac resynchronization therapy (CRT) is an accepted intervention for chronic heart failure (HF), although approximately 30% of patients are non-responders. The purpose of this study was to determine whether exercise respiratory gas exchange obtained before CRT implantation predicts early response to CRT.

Methods: Before CRT implantation, patients were assigned to either a mild-moderate group (Mod G, n = 33, age 67 ± 10 years) or a moderate-severe group (Sev G, n = 31, age 67 ± 10 years), based on abnormalities in exercise gas exchange. Severity of impaired gas exchange was based on a score from the measures of VE/VCO(2) slope, resting PETCO(2) and change of PETCO(2) from resting to peak. All measurements were performed before and 3 to 4 months after CRT implantation.

Results: Although Mod G did not have improved gas exchange (p > 0.05), Sev G improved significantly (p < 0.05) post-CRT. In addition, Mod G did not show improved right ventricular systolic pressure (RSVP; pre vs post: 37 ± 14 vs 36 ± 11 mm Hg, p > 0.05), yet Sev G showed significantly improved RVSP, by 23% (50 ± 14 vs 42 ± 12 mm Hg, p < 0.05). Both groups had improved left ventricular ejection fraction (p < 0.05), New York Heart Association class (p < 0.05) and quality of life (p < 0.05), but no significant differences were observed between groups (p > 0.05). No significant changes were observed in brain natriuretic peptide in either group post-CRT.

Conclusion: Based on pre-CRT implantation ventilatory gas exchange, subjects with the most impaired values appeared to have more improvement post-CRT, possibly associated with a decrease in RVSP.

Keywords: exercise; heart failure; pulmonary hypertension; right ventricle pressure; ventilatory efficiency.

Figure 1

The changes in MVI scores from pre to post CRT implantation in the Mod G and the Sev G groups. The Mod G (mild to moderately impaired group), the Sev G (moderate to severely impaired group). * denotes a significant group × time interaction (p<0.05).

Figure 2

The changes in LVEF (%) from pre to post CRT implantation in the Mod G and the Sev G groups. The Mod G (mild to moderately impaired group), the Sev G (moderate to severely impaired group), LVEF (left ventricle ejection fraction).

Figure 3

The changes in RVSP (mmHg) from pre to post CRT implantation in the Mod G and the Sev G groups. The Mod G (mild to moderately impaired group), the Sev G (moderate to severely impaired group), RVSP (right ventricle systolic pressure). * denotes a significant group × time interaction (p<0.05).