Michael Fong

Chronic heart failure management and remote haemodynamic monitoring

Heart failure (HF) has a large societal and economic burden and is expected to increase in magnitude and complexity over the ensuing years. A number of telemonitoring strategies exploring remote monitoring and management of clinical signs and symptoms of congestion in HF have had equivocal results. Early studies of remote haemodynamic monitoring showed promise, but issues with device integrity and implantation-associated adverse events hindered progress. Nonetheless, these early studies established that haemodynamic congestion precedes clinical congestion by several weeks and that remote monitoring of intracardiac pressures may be a viable and practical management strategy. Recently, the safety and efficacy of remote pulmonary artery pressure-guided HF management was established in a prospective, single-blind trial where randomisation to active pressure-guided HF management reduced future HF hospitalisations. Subsequent commercial use studies reinforced the utility of this technology and post hoc analyses suggest that tight haemodynamic management of patients with HF may be an additional pillar of therapy alongside established guideline-directed medical and device therapy. Currently, there is active exploration into utilisation of this technology and management paradigm for the timing of implantation of durable left ventricular assist devices (LVAD) and even optimisation of LVAD therapy. Several ongoing clinical trials will help clarify the extent and utility of this strategy along the spectrum of patient with HF from individuals with chronic, stable HF to those with more advanced disease requiring heart replacement therapy.

Effects of pressure variation and atrial fibrillation on CardioMEMS™ HF measured pulmonary artery diastolic pressure: comparison of device-averaged and visually inspected waveforms

OBJECTIVE Heart failure (HF) management guided by implantable hemodynamic monitoring reduces hospitalization rates. Hemodynamic data from the CardioMEMS™ HF system includes device-averaged pulmonary artery pressures (PAP) and heart rate. Agreement of device-averaged values compared to the standard method of visual inspection of pressure waveforms at end-expiration is unknown. We evaluated the agreement between device-averaged and visually inspected end-expiratory PAP. APPROACH Twenty-one patients implanted with the CardioMEMS™ HF system were evaluated. Eight-hundred twenty-three PAP waveforms from the Merlin remote monitoring website were visually inspected and pulmonary artery systolic pressure (PASP) and pulmonary artery diastolic pressure (PADP) at end-expiration were recorded. Waveforms were evaluated for pressure variation (PV), defined as the difference between highest and lowest PASP measurement of  ⩾20 mmHg. Bland-Altman analysis quantified differences between device-averaged and visually inspected waveforms. MAIN RESULTS All patients were NYHA functional class III, mean age was 67  ±  15 years and 15 (71%) had AF. Bland-Altman analysis of all waveforms revealed a mean-difference in PADP of  -1.4 mmHg, indicating that visually inspected values were higher than device-averaged values. For PV  ⩾20 mmHg, this value increased to  -2.8 mmHg. The mean-difference comparing waveforms from patients with or without AF was  -1.3 and  -1.6 mmHg, respectively. The 95% limits of agreement were  >50% wider for waveforms from patients with versus without AF (10.3 versus 6.7 mmHg). SIGNIFICANCE There is good agreement between device-averaged and visually inspected waveforms when pressure variation is  <20 mmHg and for patients without atrial fibrillation.

Breathing Intolerance Index and Control of Ventilation, a Non-invasive Method for Evaluating Inspiratory Muscle Endurance at Rest and Exercise, in Patients with Cardiomyopathy: One Year Follow-up

Rationale: Inspiratory muscle endurance as expressed by the tension-time index of the diaphragm [TTI=(Pdi/ Pdimax) × (Ti/Ttot)] in normal subjects and cardiorespiratory disorders requires the use of esophageal and gastric balloons. A noninvasive technique can be used in which the ratio of tidal volume to vital capacity (Vt/VC) is substituted for Pdi/Pdimax, with the resulting relationship [(Ti/Ttot) × (Vt/FVC)] called the breathing intolerance index (BIT). The response to medical management of BIT in patients with cardiomyopathy with chronic heartfailure has not been assessed before and after medical management. Objectives: To compare control of ventilation and BIT in patients with stable dilated cardiomyopathy at rest and exercise, and to analyze BIT, oxygen uptake and carbon dioxide elimination at baseline and approximately one year after initiating medical management. Methods: Control of ventilation and BIT were assessed in 24 patients (mean age 55.5 years; 17 males) at rest and at peak exercise during bicycle ergometry, at baseline and approximately 14 months later. Results: Median peak VO2 was 12.9 mL/kg/min and 14.3 mL/kg/min at baseline and followup, respectively (p<0.036, adjusted for age, gender and BMI). It increased 4.3 times from rest to peak exercise at baseline and 4.7 times at followup (NS). Peak V’O2 increased by 10.5% between baseline and followup (p=0.036 after adjusting for age, sex and BMI). BIT did not change significantly. Peak V’O2/BIT increased significantly from baseline to follow-up (p=0.008, adjusted for age, sex and BMI). No patients died or experienced acute heart failure during the study. Conclusions: Peak V’O2 in relation to non-invasively measured peak tension-time index of the respiratory muscles (BIT) increases significantly after one year of medical management, indicating increased efficient oxygen utilization as cardiac function improves. BIT is useful for noninvasively assessing inspiratory muscle endurance and relating oxygen uptake to ventilation in patients with dilated cardiomyopathy and chronic congestive heart failure

Breathing Intolerance Index (BIT) and its Relation to Exercise Data: Noninvasive Assessment of Inspiratory Muscle Endurance during Rest and Exercise in Patients with Chronic Obstructive Pulmonary Disease and Cardiovascular Disorders

Rationale: Diaphragmatic tension-time index [TTdi = (Pdi/Pdimax)(Ti/ Ttot)] assesses inspiratory muscle endurance during rest and exercise. However, the procedure is invasive and not practical for general use. Recently, Tidal Volume/Vital Capacity (Vt/VC) has been substituted for Pdi/Pdimax, to assess need for assisted ventilation in chronic respiratory disorders. This technique has not been used to assess respiratory muscle endurance in other conditions during rest and exercise. Objective: To compare control of ventilation and BIT in cardiorespiratory disorders and controls and to assess their relation to oxygen uptake (V’O2) and annual acute decompensations. Methods: BIT and V’O2 were assessed in patients with stable CVD (n = 20), RD (n = 20) and C (n = 20) during bicycle ergometry. ANOVA assessed differences in variables amongst cohorts at rest and peak exercise. Results: Resting BIT was [median (25th, 75th percentiles)] 0.06 (0.04, 0.07), 0.06 (0.04, 0.09) and 0.04 (0.03, 0.05) for CVD, COPD and controls, respectively. Compared to resting, BIT increased by 3.0- to 4.6- fold at peak exercise in all cohorts (p < 0.0001). V’O2max exceeded resting values by 7.5-, 4.6-, and 9.4- fold in COPD, CVD and C, respectively (all p < 0.0001). When corrected for BIT (V’O2/BIT), controls exhibited significantly greater (V’O2/BIT) max than CVD and COPD (p < 0.0001). Amongst patients who acutely decompensated, BIT was higher only in resting CVD patients (p < 0.019). Conclusions: BIT is useful for evaluating respiratory muscle effort during rest and exercise in CVD and COPD. Oxygen uptake fails to increase in proportion to BIT in these conditions as much as in controls, reflecting impaired oxygen utilization. Its potential usefulness in predicting acute decompensations should be assessed in larger prospective studies.