The usefulness of continuous hemodynamic monitoring to guide therapy in patients with cardiopulmonary disease

Abstract

Introduction: Cardiovascular disease, whether secondary to myocardial injury, pulmonary hypertension or renal failure, have high morbidity and mortality. New treatments have improved quality of life and survival, but hospitalization rates remain high. Continuous hemodynamic monitoring allows for a new perspective in cardiovascular disease management allowing for treatment strategies based on measurements performed while the patient tends to normal daily activities.

Feasibility: Hemodynamic monitoring by the means of an implanted pressure sensor has been shown earlier to be accurate in pressure measurement, safe to implant and stable in measurements over long-term. This thesis looked at acute and long-term stability of an oxygen sensor measuring mixed venous oxygen saturation from the right ventricle (Study I). The oxygen sensor was implanted in nine patients with a conventional pacemaker indication and showed a good correlation compared levels over six years. Study II established that one data point, the night-time minimum, from the 24-hour hemodynamic trend replicated hemodynamic values collected during a controlled changes over time. In addition to the fully implanted lead and memory device, the hemodynamic monitoring system includes remote monitoring, e.g. sending the data stored in the implantable hemodynamic monitor to a secured website for review by the treating clinician. Study III described this telemonitoring system and demonstrated that the transmission rate was acceptable and apparently independent of age and disease stage.

Applicability: In patients with heart failure, peak VO2 has been shown to be a good predictor of outcome. However, maximal exercise tests are cumbersome to perform and involve risk for the patients. Submaximal tests, e.g. 6-minute walk tests are routinely used to evaluate patient status in the hospital clinic. Study IV compared hemodynamic response during maximal and submaximal exercise in 30 patients with heart failure. During submaximal exercise the pressures increased 70-80% and heart rate 90% of the change achieved during maximal exercise. Thus, submaximal exercise hemodynamic response could be a tool in patient assessment in patients inhaled prostacyclin analog, iloprost. The effect of the drug lasted shorter when the patients used the treatment at home than under supervision in the hospital. The treatment effect in both setting was shorter than previously demonstrated in other studies. The most probable explanation for this is that hemodynamic measurements occurred during normal, daily activities. in Study V, while earlier measurements have been performed in stationary patients during invasive studies. Study VI found progressively increasing cardiac pressures between hemodialysis treatments in 16 patients with end stage renal disease. The pressure increase, especially after a weekend when hemodialysis treatment was withheld for an extra day, was in the same magnitude as seen in patients with heart failure before a volume overload event leading to hospitalization. These recurrent changes in cardiac pressures might result in myocardial damage. More frequent dialysis treatment might be.

Conclusion: The hemodynamic monitoring system and its components are feasible and mixed venous oxygen might add value to the system. One single data point could be extracted from the advise the clinician of possible changes in the hemodynamic trends. This thesis supports the use of implantable hemodynamic monitoring in patients with cardiovascular disease of different origin associated with compromised hemodynamics. These observations may help to evaluate disease progress and to make therapeutic decisions.