# Long-Term Effects of High-Intensity Interval Training (HIIT) on Cardiac Function and Mortality in Heart Failure

PMID: 41084708
Journal: Cureus
Published: 2025-09-10
Authors: Seby M, Vayolipoyil S, Akbar M, Ahmed A, A M Imam M, Nafees S, Shah N, Azad A, Aashan M

## 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.

## Population

- Adults aged 30 years and older with confirmed heart failure and medical clearance for HIIT rehabilitation.
- Sample size: 158
- Age: Mean 56.3 +/- 12.4 years; 42% were 60 years or older.
- Sex: 113 men (71%) and 45 women (29%).
- Fitness level: Clinical rehabilitation population; functional capacity measured by DASI.
- Health status: Heart failure, including HFrEF, HFpEF, and unknown HF type; common comorbidities included hypertension and diabetes.

## Methodology

- Longitudinal observational cohort with repeated measures at baseline, three months, and six months.
- Six months, with data collected from July 2024 to January 2025.
- Cardiac department of Pakistan Institute of Medical Sciences, Islamabad, Pakistan.

## Protocol

- Self-reported HIIT participation.
- Intensity: Self-reported perceived intensity; no prescribed target.
- Session duration: Assessed by questionnaire but not reported as a protocol.
- Frequency: Assessed by questionnaire but not reported as a protocol.
- Program length: Observed over six months.

## Outcomes

### HIIT participation and functional capacity
Status: improved
Higher HIIT participation correlated with higher DASI scores.

r=0.392, p<0.01.

### HIIT participation and quality of life
Status: improved
Higher HIIT participation correlated with higher KCCQ scores.

r=0.215, p<0.01.

### HIIT participation and NYHA class
Status: improved
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
Status: improved
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
Status: improved
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
Status: worse/safety concern
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.

## Practical 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 And Adherence

- 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.

## Original Sources

- [PubMed](https://pubmed.ncbi.nlm.nih.gov/41084708/) (pubmed)
- [DOI](https://doi.org/10.7759/cureus.91972) (doi)
- [PMC full text](https://www.ncbi.nlm.nih.gov/pmc/articles/PMC12515264/) (full text)

## Agent Guidance

Preserve the paper-level scope of this note. Do not generalize beyond the population, protocol, measured outcomes, and limitations above.