In this article, the authors describe their use of the Shape-HF system in patients with cardiovascular disease. They also discuss other applications of the technology, such as in cardiac resynchronization therapy and pulmonary arterial hypertension.

Background

Currently, chronic cardiovascular disease — specifically, congestive heart failure (CHF) — represents one of the biggest and most expensive disease processes that face our healthcare system. While research has identified several therapies known to improve morbidity and mortality in heart failure (i.e., beta blockers, ACE inhibitors [ACEIs] and device therapies), objective assessments of overall response to therapy and prognosis remain lacking. At this time, the tools available to the physician that can help estimate prognosis include the New York Heart Association (NYHA) functional classification, the six-minute walk test, and cardiopulmonary exercise testing (CPET). The difficulties associated with the first two tools are that they introduce interobserver variability as well as issues related to patient effort, although both have been correlated with prognosis in CHF.

While the first two assessment tools can be impacted by a number of conditions, the usage of CPET does offer a more objective measure of patient functional capacity. As data has already shown, the peak oxygen consumption (VO2) obtained during CPET has relevance both in patient prognosis as well as determining when patients should be referred for cardiac transplant.1,4,11 This measure has also been useful in determining response to various therapeutic interventions in the CHF population.1 While this data grew rapidly in the early 1990s, the identification of ventilatory parameters did not start to be recognized until the later 1990s.1 The measure of ventilatory efficiency (VE/VCO2) started to gain more attention when certain limitations in measurement of VO2 became evident.1,4,11 In particular, some studies have suggested that measurements of peak VO2 were not reflective of the addition of beta blockers, whereas the VE/VCO2 slope retains its prognostic significance despite medical therapy for CHF.1,11 In addition, the measurement of peak VO2 has required patients to achieve maximal exertional capacity, which is difficult given the nature of the disease processes being investigated.

The Shape System

At the University of Illinois at Chicago (UIC), we have been able to obtain early experience with a submaximal cardiopulmonary exercise system (Shape Medical Systems, Inc., St. Paul, MN) (Figure 1). While the data supporting the usage of cardiopulmonary testing at maximal exercise are robust, there are limitations to its usage as previously identified. Measures such as VE/VCO2, oxygen pulse (VO2/HR), oxygen uptake efficiency (VO2/log VE), and partial pressure of end-tidal carbon dioxide (ETCO2), have already been shown to carry significant prognostic value.1,2 Additionally, other measures such as heart rate recovery and chronotropic response index provide additional useful information. Combining these measures, already clinically proven in prior studies of CHF, along with the innovation of measurement at submaximal exercise, we believe make the Shape system particularly appealing for clinical use.