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Exercise oxygen pulse kinetics in patients with hypertrophic cardiomyopathy
Massimo Mapelli1,2, Simona Romani1, Damiano Magrì3
1Heart Failure Unit, Centro Cardiologico Monzino Istituto di Ricovero e Cura a Carattere Scientifico, Milano, Lombardia, Italy.
Insights
An abnormal O2-pulse temporal behavior during exercise in hypertrophic cardiomyopathy (HCM) patients indicates reduced functional capacity and advanced disease, regardless of left ventricle outflow tract obstruction (LVOTO). This finding helps identify exercise-limited individuals more effectively.
Area of Science:
- Cardiology
- Exercise Physiology
- Biomedical Engineering
Background:
- Reduced cardiac output (CO) is implicated in hypertrophic cardiomyopathy (HCM) symptom development.
- O2-pulse (oxygen uptake/heart rate) and VO2/work relationship reflect stroke volume (SV) and CO changes during exercise.
Purpose of the Study:
- To investigate if O2-pulse kinetics and VO2/work relationship during cardiopulmonary exercise testing (CPET) can identify exercise-limited HCM patients.
- To correlate CPET parameters with left ventricle outflow tract obstruction (LVOTO) in HCM.
Main Methods:
- Retrospective analysis of CPET data from 312 non-end-stage HCM patients across three clinical units.
- Evaluation of O2-pulse absolute values and temporal behavior, VO2/work relationship, and standard CPET parameters.
- Patients were grouped based on resting or Valsalva-induced LVOTO levels.
Main Results:
- No significant association was found between standard CPET parameters (absolute or dynamic) and LVOTO.
- 31% of HCM patients exhibited abnormal O2-pulse temporal behavior, independent of LVOTO.
- These patients demonstrated lower peak systolic pressure, workload, VO2, and O2-pulse, with a higher VE/VCO2 slope.
Conclusions:
- Abnormal O2-pulse temporal behavior during exercise, reflecting inadequate SV increase, correlates with reduced functional capacity in HCM.
- This parameter identifies more advanced HCM disease, irrespective of LVOTO status.
- Standard CPET parameters are insufficient for identifying exercise limitation related to LVOTO in HCM.
Objectives:
Reduced cardiac output (CO) has been considered crucial in symptoms' genesis in hypertrophic cardiomyopathy (HCM). Absolute value and temporal behaviour of O2-pulse (oxygen uptake/heart rate (VO2/HR)), and the VO2/work relationship during exercise reflect closely stroke volume (SV) and CO changes, respectively. We hypothesise that adding O2-pulse absolute value and kinetics, and VO2/work relationship to standard cardiopulmonary exercise testing (CPET) could help identify more exercise-limited patients with HCM.
Methods:
CPETs were performed in 3 HCM dedicated clinical units. We retrospectively enrolled non-end-stage consecutive patients with HCM, grouped according to left ventricle outflow tract obstruction (LVOTO) at rest or during Valsalva manoeuvre (72% of patients with LVOTO <30; 10% between 30 and 49 and 18% ≥50 mm Hg). We evaluated the CPET response in HCM focusing on parameters strongly associated with SV and CO, such as O2-pulse and VO2, respectively, considering their absolute values and temporal behaviour during exercise.
Results:
We included 312 patients (70% males, age 49±18 years). Peak VO2 (percentage of predicted), O2-pulse and ventilation to carbon dioxide production (VE/VCO2) slope did not change across LVOTO groups. Ninety-six (31%) patients with HCM presented an abnormal O2-pulse temporal behaviour, irrespective of LVOTO values. These patients showed lower peak systolic pressure, workload (106±45 vs 130±49 W), VO2 (21.3±6.6 vs 24.1±7.7 mL/min/kg; 74%±17% vs 80%±20%) and O2-pulse (12 (9-14) vs 14 (11-17) mL/beat), with higher VE/VCO2 slope (28 (25-31) vs 27 (24-31)) (p<0.005 for all). Only 2 patients had an abnormal VO2/work slope.
Conclusion:
None of the frequently used CPET parameters, either as absolute values or dynamic relationships, were associated with LVOTO. Differently, an abnormal temporal behaviour of O2-pulse during exercise, which is strongly related to inadequate SV increase, correlates with reduced functional capacity (peak and anaerobic threshold VO2 and workload) and increased VE/VCO2 slope, identifying more advanced disease irrespectively of LVOTO.
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