Background
Heart failure is a common chronic condition in which the heart cannot pump blood as effectively as the body needs. Many patients with heart failure also develop abnormal heart rhythms, called arrhythmias. These can range from atrial fibrillation, which causes the upper chambers of the heart to beat irregularly, to bradyarrhythmias, which are abnormally slow rhythms, and ventricular tachyarrhythmias, which can be dangerous and sometimes life-threatening.
In everyday clinical practice, arrhythmias may go unnoticed unless they cause symptoms or are captured on an electrocardiogram. That means the true burden of arrhythmia in patients with heart failure has often been underestimated, especially in ambulatory patients who are not hospitalized and who do not already have a cardiac implantable electronic device such as a pacemaker or defibrillator. Another open question has been whether device-guided remote congestion management, which is designed to help clinicians detect worsening fluid overload earlier, changes the frequency of arrhythmias.
The ALLEVIATE-HF trial, formally called Algorithm Using LINQ Sensors for Evaluation And Treatment of Heart Failure, was designed to address these gaps. It used continuous monitoring with an insertable cardiac monitor, or ICM, to observe arrhythmias over time and to see how these rhythm findings related to treatment decisions and later clinical events.
Study Design
This analysis included 711 patients with symptomatic heart failure, New York Heart Association functional class II or III, and a recent heart failure event. Patients could have any ejection fraction, meaning the study included both heart failure with preserved ejection fraction and heart failure with reduced ejection fraction. None of the patients had a prior cardiac implantable electronic device at baseline.
All participants underwent implantation of an insertable cardiac monitor. They were then randomized to one of two strategies for congestion management: an ICM-guided, physician-directed, nurse-facilitated strategy or usual care. In both groups, investigators could access arrhythmia data, and management of arrhythmia was left to the treating clinicians. This is important because the study was not designed to force a specific antiarrhythmic treatment pathway, but rather to observe what happened in real-world practice under close rhythm surveillance.
The average age of participants was 70.5 years, and 45.7% were women. The mean follow-up was 17.3 months. Most patients, 67.9%, had heart failure with preserved ejection fraction, and 60.2% were in NYHA class II at baseline.
Main Findings
During the 13-month randomized phase, the rate of arrhythmia occurrence did not differ between the study groups. In other words, the congestion-management strategy guided by the implantable monitor did not appear to reduce or increase the overall burden of arrhythmia compared with usual care.
However, the overall arrhythmia burden observed by continuous monitoring was substantial. Over three years, atrial fibrillation occurred in 66.6% of patients. New-onset atrial fibrillation developed in 25.4%. Bradyarrhythmias occurred in 47.1% of patients, and ventricular tachycardia or ventricular fibrillation occurred in 20.1%.
These numbers are clinically meaningful. Atrial fibrillation is the most common sustained arrhythmia in heart failure and can worsen symptoms, increase stroke risk, and complicate medication management. Bradyarrhythmias may contribute to fatigue, dizziness, or syncope and sometimes require pacing therapy. Ventricular tachycardia and fibrillation are more serious because they can lead to sudden cardiac death, especially in vulnerable patients with structural heart disease.
Relationship Between Rhythm Findings and Clinical Actions
One of the most important observations from ALLEVIATE-HF was that arrhythmias detected by the insertable monitor were strongly associated with later clinical interventions. When the monitor recorded an arrhythmia, the likelihood of a subsequent arrhythmia-related intervention increased substantially.
The hazard ratio for any arrhythmia recorded by the ICM and a later arrhythmia-related intervention was 3.81. More specifically, ventricular tachycardia or fibrillation was associated with ventricular arrhythmia-related intervention with a hazard ratio of 7.04; atrial fibrillation was associated with AF-related intervention with a hazard ratio of 3.28; and bradyarrhythmia was associated with bradyarrhythmia-related intervention with a hazard ratio of 7.22. All of these associations were highly statistically significant.
In practical terms, this means continuous rhythm monitoring did not just generate data; it helped identify clinically actionable events. Physicians responded to these rhythm abnormalities with therapies such as medication changes, anticoagulation decisions for atrial fibrillation, device implantation when indicated, and catheter ablation in selected patients.
Over the course of follow-up, therapeutic cardiac implantable electronic device implantation occurred in 22.7% of patients, and ablation procedures occurred in 26.1%. This shows that a considerable fraction of patients eventually needed rhythm-directed therapy after arrhythmias were identified.
Association With Hospitalization and Heart Failure Events
The study also found that arrhythmias detected on continuous monitoring were associated with worse clinical outcomes. Patients with ICM-recorded arrhythmia had a higher risk of all-cause hospitalization, with a hazard ratio of 1.79, and a higher risk of heart failure events, with a hazard ratio of 1.69.
This does not prove that arrhythmia directly caused every hospitalization or heart failure event, but it strongly suggests that arrhythmias are markers of clinical instability and may contribute to worsening symptoms, hemodynamic compromise, or care escalation. For clinicians, the message is that rhythm abnormalities in heart failure should not be treated as incidental findings. They may reflect a broader deterioration in cardiovascular status.
Differences by Ejection Fraction
The researchers also examined how arrhythmia patterns differed according to left ventricular ejection fraction. Bradyarrhythmias were more common in patients with ejection fraction of 50% or higher, while ventricular tachyarrhythmias were more frequent in those with ejection fraction below 50%. Atrial fibrillation occurred at similar rates in both groups.
This pattern is consistent with the idea that different forms of heart failure may carry different rhythm risks. Patients with preserved ejection fraction tend to be older and have more comorbidities, which may help explain the higher rate of slow rhythms and conduction disease. Patients with reduced or mildly reduced ejection fraction often have more structural heart disease and myocardial scar, which can predispose them to ventricular arrhythmias.
Clinical Interpretation
The key clinical takeaway from ALLEVIATE-HF is that continuous monitoring uncovered a large burden of arrhythmias in patients with symptomatic heart failure, even when they were not implanted with a pacemaker or defibrillator at baseline. These arrhythmias were not reduced by the study’s congestion-management strategy, suggesting that fluid management alone is not enough to prevent rhythm disturbances.
At the same time, the monitoring strategy had practical value. It identified arrhythmias that led to meaningful treatment changes and was associated with subsequent hospitalization and heart failure events. In this sense, the ICM functioned as both a diagnostic tool and an early warning system.
For clinicians, the findings support a more proactive approach to rhythm surveillance in selected patients with heart failure, especially those with recent decompensation, unexplained symptoms, or concern for occult arrhythmia. The study also reinforces the importance of considering arrhythmia when symptoms worsen, even if overt palpitations are absent.
What This Means for Patients
For patients living with heart failure, the study highlights a simple but important message: abnormal heart rhythms may be present even when they are not felt. A person may not notice atrial fibrillation, bradycardia, or intermittent ventricular arrhythmias, yet these problems can still affect health and treatment decisions.
Continuous monitoring can help doctors detect these changes sooner. Depending on the rhythm problem found, treatment might include adjusting heart failure medications, starting blood thinners to lower stroke risk in atrial fibrillation, considering pacing support for slow heart rhythms, or evaluating for ablation or more advanced device therapy.
However, monitoring is only one piece of care. It does not replace good heart failure management, which still includes guideline-directed medical therapy, blood pressure control, attention to salt and fluid balance, management of comorbid conditions, and close follow-up after hospitalizations.
Limitations
As with any clinical study, there are limitations to keep in mind. The investigators could access arrhythmia data in both study arms, which may have reduced differences between the randomized strategies. The study was also conducted in a specific population of older patients with recent heart failure events, so results may not apply equally to younger patients or those with more stable disease.
In addition, arrhythmia detection by implantable monitors is highly sensitive, but not every detected episode necessarily translates into a major clinical event. Some findings may lead to intervention because they are concerning, even if the patient is not having obvious symptoms. That is both a strength and a challenge of continuous monitoring: it improves detection, but it also raises questions about which episodes truly require action.
Conclusion
In ambulatory patients with symptomatic heart failure and a recent heart failure event, the arrhythmia burden was high and was not changed by the protocol-directed congestion-management strategy used in ALLEVIATE-HF. Continuous insertable cardiac monitor surveillance revealed frequent atrial fibrillation, bradyarrhythmias, and ventricular tachyarrhythmias, and these findings were closely linked to treatment changes, hospitalization, and heart failure events.
The study suggests that arrhythmia surveillance may have an important role in the care of selected heart failure patients, particularly those at higher risk for rhythm instability. More broadly, it reinforces the concept that heart failure management should address not only congestion and medications, but also the rhythm disorders that often travel with the disease.