Long-Term Effects of High-Intensity Interval Training (HIIT) on Cardiac Function and Mortality in Heart Failure
Question
What are the long-term associations between HIIT participation and cardiac functional capacity, quality of life, symptom burden, and mortality-related outcomes in adults with heart failure over six months?
Summary
This longitudinal observational study followed 158 adults with heart failure at a cardiac department in Islamabad, Pakistan, over six months. All enrolled participants were already receiving structured HIIT as part of rehabilitation, but the study did not prescribe or standardize an interval protocol; HIIT exposure was captured by self-report for weekly sessions, session duration, months of participation, and perceived intensity. Higher HIIT participation correlated with better Duke Activity Status Index scores, better Kansas City Cardiomyopathy Questionnaire scores, and lower symptom severity by NYHA class, while repeated measures showed KCCQ and DASI improved over time but NYHA class worsened. The design supports association and longitudinal tracking, not causal comparison with MICT or usual care.
Methodology
- Adults aged 30 years and older with confirmed heart failure and medical clearance for HIIT rehabilitation.
- 158 participants.
- Intensity: Self-reported perceived intensity; no prescribed target.
- Assessed by questionnaire but not reported as a protocol.
- Assessed by questionnaire but not reported as a protocol.
- Observed over six months.
- Longitudinal observational cohort with repeated measures at baseline, three months, and six months.
- Kansas City Cardiomyopathy Questionnaire-12, Duke Activity Status Index, New York Heart Association class, and HIIT participation were tracked.
Outcomes
HIIT participation and functional capacity
Higher HIIT participation correlated with higher DASI scores.
r=0.392, p<0.01.
HIIT participation and quality of life
Higher HIIT participation correlated with higher KCCQ scores.
r=0.215, p<0.01.
HIIT participation and NYHA class
Higher HIIT participation correlated with lower NYHA class, interpreted as less symptom severity.
Reported as r=-0.265 in abstract/table, p<0.01.
KCCQ over time
KCCQ improved from baseline to six months.
28.84 +/- 3.63 at T1 to 30.22 +/- 3.89 at T3; F(2,314)=6.64, p=0.002, partial eta2=0.041.
DASI over time
DASI improved from baseline to six months.
15.42 +/- 1.92 at T1 to 16.74 +/- 1.87 at T3; F(2,314)=11.12, p<0.001, partial eta2=0.066.
NYHA class over time
NYHA class scores increased over time, indicating worse functional class.
2.49 +/- 0.58 at T1 to 2.82 +/- 0.61 at T3; F(2,314)=13.52, p<0.001, partial eta2=0.079.
Insights
- This article is useful as clinical background for monitoring and clearance requirements in heart failure, not as a source for exact HIIT programming.
- Self-reported HIIT participation may track with better quality of life and functional capacity in heart failure rehabilitation.
- Heart failure exercise content should avoid claiming causal benefit from this study because there was no control group or standardized protocol.
Limitations
- Observational design does not permit causal inference.
- No control group or comparator intervention.
- HIIT protocol was not prescribed or standardized.
- HIIT exposure was self-reported.
- Purposive non-probability sampling.
- Final sample size was lower than planned.
- Single clinical setting limits generalizability.
- Detailed adverse event, adherence, and mortality results were not reported.
Safety
- Medical clearance was required for HIIT enrollment.
- Recent acute cardiac events in the previous four weeks and unsafe comorbid illness were exclusion criteria.
- No detailed adverse event table or adverse event rate was reported.
- NYHA class worsened over six months despite improvements in KCCQ and DASI.