CRT: Can This Heart Therapy Improve Your Long-Term Health?
"Explore how cardiac resynchronization therapy (CRT) can help patients with heart failure, focusing on echocardiographic assessments and long-term outcomes."
Heart failure (HF) is a significant global health concern, affecting millions worldwide and leading to frequent hospitalizations. In Brazil alone, tens of thousands are admitted each year due to HF. A common issue among HF patients is intraventricular conduction disturbances, where electrical signals in the heart are not properly synchronized. This often leads to a condition called cardiac dyssynchrony, impairing the heart's ability to pump blood efficiently.
Cardiac resynchronization therapy (CRT) has emerged as a valuable treatment option for individuals with advanced heart failure. CRT involves implanting a device that helps to coordinate the contractions of the heart's ventricles, improving its overall function. Identifying which patients will benefit most from CRT has been a key focus of research, with echocardiography playing a crucial role in both patient selection and therapy assessment.
Echocardiography, a non-invasive imaging technique using ultrasound, allows doctors to visualize the heart's structure and function. It helps in determining the extent of dyssynchrony and assessing the impact of CRT on cardiac performance. A recent study investigated the use of echocardiography to evaluate CRT outcomes over a two-year period, providing insights into the therapy's effectiveness and potential predictors of success.
CRT’s Role in Heart Failure
Approximately 6.7 million Americans over age 20 have heart failure, and the Heart Failure Society of America expects prevalence to reach 8.7 million by 2030. Heart failure contributed to 425,147 deaths, or 45% of cardiovascular deaths in the United States, in 2022. Cardiac resynchronization therapy is an established treatment for selected heart failure patients with electrical dyssynchrony and is associated with improved left ventricular ejection fraction, fewer ventricular arrhythmias, better symptoms, and improved survival.
Established Therapy, Uneven Response
CRT typically uses biventricular pacing to coordinate contraction in appropriately selected patients with heart failure and electrical dyssynchrony. It has reduced morbidity and mortality, reversed left ventricular remodeling, and improved quality of life, but some patients show no clinical improvement or reverse remodeling after implantation. Limitations include suboptimal patient selection, incomplete characterization of conduction disease, and fragmented post-implant care with poor communication between specialties.
From Advanced HF to Broader Use
CRT became an accepted treatment for heart failure patients with impaired left ventricular function and a wide QRS complex. It was revolutionary for people with advanced heart failure who previously had few options beyond cardiac transplantation, and it later became a realistic option for patients with mild heart failure. The CARE-HF and COMPANION randomized controlled trials subsequently evaluated long-term effects on morbidity and mortality, while REVERSE studied patients with NYHA class II-III symptoms.
How Does Echocardiography Help Assess CRT Effectiveness?
The study, published in the Arq Bras Cardiol in 2010, followed 20 patients who underwent CRT, with assessments conducted over two years. Researchers used echocardiography to evaluate various parameters, including the heart's ejection fraction (the percentage of blood pumped out with each contraction), the degree of intraventricular dyssynchrony, and overall heart function. Patients also completed questionnaires to assess their quality of life and underwent walking tests to measure their exercise capacity.
- Mortality: 25% of patients (5 individuals) died during the two-year follow-up. A significant number of these deaths were linked to cardiomyopathy caused by Chagas' disease.
- Ejection Fraction: While there was no immediate change in ejection fraction after CRT implantation, a significant improvement was observed two years later.
- Intraventricular Dyssynchrony: An initial worsening of dyssynchrony was noted shortly after the procedure, but long-term assessments showed that tissue Doppler imaging could predict CRT efficiency in relation to death rate.
- Quality of Life: Patients who died reported a higher score on the “Minnesota Living with Heart Failure Questionnaire,” indicating a poorer quality of life.
Long-Term Response Signals
In a study examining echocardiographic mechanical dyssynchrony after CRT, atrial regurgitation and/or systolic dysfunction disappeared in 256 patients, representing 83.4% of the study population. Overall mean survival was 95.9 ± 52.9 months. Mean survival was longer in women than in men, at 109.1 ± 52.4 versus 90.9 ± 52.4 months, and in patients younger than 60 years than in older patients, at 110.6 ± 53.7 versus 88.6 ± 51.1 months.
When CRT May Not Help
In patients with systolic heart failure and a QRS duration below 130 milliseconds, CRT did not reduce death or heart-failure hospitalization and may have increased mortality. The PROSPECT trial also had an important limitation: its observational, nonrandomized design assessed the predictive ability of echocardiographic parameters rather than whether using those parameters improved clinical outcomes. Other research suggests that clinical response may vary by the underlying cause of heart failure, but further research is needed to clarify confounding factors and mechanisms.
CRT-D Versus Defibrillator Therapy
In a seven-year follow-up of patients with mild heart failure and left bundle-branch block, the cumulative rate of death from any cause was 18% among those assigned to CRT-D and 29% among those assigned to defibrillator therapy alone. The adjusted hazard ratio for death in the CRT-D group was 0.59, with a 95% confidence interval of 0.43 to 0.80 and P<0.001. Reviews describe CRT as improving hemodynamics and quality of life in patients with heart failure and electrocardiography-defined ventricular dyssynchrony, although up to 30% of patients may fail to respond to biventricular pacing.
The Future of CRT Assessment
While this study provides valuable insights, the authors acknowledge limitations such as a small sample size and the absence of a control group. They also point out that more advanced echocardiography techniques, like three-dimensional imaging and strain analysis, could further enhance CRT evaluation. As technology evolves, these advanced methods may play a more significant role in optimizing patient selection and improving long-term outcomes for individuals undergoing cardiac resynchronization therapy.
Optimization in Real-World Care
Clinical outcomes may depend on how CRT is sequenced with guideline-directed medical therapy, because optimal sequencing remains uncertain and difficulties with medication uptitration can delay treatment. One in-hospital CRT program combined comprehensive heart-failure evaluation with systematic echocardiography-guided optimization, with implanted patients referred for the program 3 to 12 months after implantation. Real-world studies have also evaluated whether CRT optimization affects heart-failure hospitalizations and related costs.