Overview
Heart failure is a chronic condition in which the heart cannot pump blood as effectively as the body needs. Many people with heart failure also experience abnormal heart rhythms, or arrhythmias, which may be silent or may cause palpitations, dizziness, worsening shortness of breath, fainting, or even sudden clinical deterioration. In ambulatory patients with symptomatic heart failure who do not already have a cardiac implantable electronic device, the true burden of arrhythmias has been difficult to measure. It has also been unclear whether a remote congestion-management strategy guided by implanted monitoring devices can reduce arrhythmia occurrence.
The ALLEVIATE-HF trial addressed these questions by using continuous insertable cardiac monitor, or ICM, surveillance in patients with recent symptomatic heart failure events. The study provides an important real-world view of how often arrhythmias occur, how they relate to clinical outcomes, and how often they lead to treatment changes.
Why This Study Matters
Heart failure management increasingly relies on monitoring symptoms, weight, blood pressure, and sometimes device data to detect fluid retention, or congestion, before patients worsen. However, arrhythmias are another major driver of instability in heart failure. Atrial fibrillation can reduce the heart’s pumping efficiency and increase stroke risk. Bradyarrhythmias, which are too-slow rhythms, can cause fatigue, dizziness, and syncope. Ventricular tachycardia and fibrillation are potentially life-threatening rhythms that may lead to sudden cardiac death.
In many patients, these rhythms are intermittent and easily missed by routine clinic visits or short-term ECG testing. Continuous ICM monitoring offers a more complete picture, especially in patients without pacemakers, defibrillators, or other implanted rhythm devices. The key question was not only how often arrhythmias occur, but also whether finding them changes care in meaningful ways.
Study Design
ALLEVIATE-HF enrolled 711 patients with NYHA functional class II or III heart failure, any ejection fraction, and a recent heart failure event. The average age was 70.5 years, 45.7% were women, and the mean follow-up was 17.3 months. Most patients, 67.9%, had heart failure with preserved ejection fraction, and 60.2% were NYHA class II at baseline.
All participants underwent implantation of an ICM. They were then randomized to one of two congestion-management strategies: an ICM-guided, physician-directed, nurse-facilitated approach or usual care. Importantly, arrhythmia data were available to investigators in both study arms, and arrhythmia management was directed by clinicians rather than strictly by the study algorithm.
Arrhythmia occurrence was estimated with Kaplan-Meier methods. The study also examined whether ICM-detected arrhythmias were linked to later therapeutic interventions and clinical events using time-varying Cox models. This approach helps capture how changing rhythm status over time relates to changing risk.
Main Findings
During the 13-month randomized phase, the rate of arrhythmia occurrence did not differ between the study arms. In other words, the protocol-directed congestion-management strategy did not appear to reduce or increase arrhythmia burden compared with usual care.
Over 3 years, the overall occurrence of atrial fibrillation was 66.6%. New-onset atrial fibrillation occurred in 25.4% of patients. Bradyarrhythmia occurred in 47.1% of patients, and ventricular tachycardia or fibrillation occurred in 20.1%. These numbers show that clinically important rhythm disturbances were common in this heart failure population, even among patients without pre-existing implanted rhythm devices.
A key finding was that ICM-recorded arrhythmias were strongly associated with later treatment changes. When any arrhythmia was detected, the risk of a subsequent arrhythmia-related intervention increased substantially. The hazard ratio was 3.81 for arrhythmia overall. When broken down by rhythm type, the associations were also strong: VT/VF and related interventions, HR 7.04; atrial fibrillation and AF-related interventions, HR 3.28; bradyarrhythmia and bradyarrhythmia-related interventions, HR 7.22. All of these associations were statistically significant with P < 0.001.
ICM-detected arrhythmia was also associated with worse clinical outcomes. The risk of all-cause hospitalization increased by 79% (HR 1.79; P < 0.001), and the risk of heart failure events increased by 69% (HR 1.69; P = 0.003). These findings suggest that rhythm disturbances are not just incidental findings; they may signal broader instability in patients with heart failure.
What Treatments Followed Detection?
The study found that arrhythmia detection often led to meaningful intervention. Therapeutic cardiac implantable electronic device implantation occurred in 22.7% of patients, and catheter ablation occurred in 26.1%.
In practical terms, this means that many patients required escalation of care after arrhythmias were identified. Examples may include pacemaker implantation for clinically important bradyarrhythmias, defibrillator consideration in selected high-risk patients, rhythm-control therapy for atrial fibrillation, or ablation procedures for recurrent symptomatic or clinically significant arrhythmias.
This result is important because it shows that continuous monitoring can uncover actionable findings rather than simply increasing diagnostic noise. Still, the optimal response to each arrhythmia depends on symptoms, heart failure phenotype, comorbidities, and patient preference.
Differences by Ejection Fraction
The investigators also examined how arrhythmia type varied by left ventricular ejection fraction, a measure of pumping function. Bradyarrhythmias were more common in patients with ejection fraction 50% or higher, while VT/VF occurred more frequently in those with ejection fraction below 50%. Atrial fibrillation occurred at similar rates in both groups.
This pattern is clinically plausible. Patients with preserved ejection fraction are often older and may have more conduction system disease, which can predispose to slow rhythms. Patients with reduced or mildly reduced ejection fraction may be more vulnerable to ventricular arrhythmias because of structural heart disease, myocardial scar, or adverse remodeling. Atrial fibrillation remains common across the heart failure spectrum.
Clinical Interpretation
The ALLEVIATE-HF trial suggests several important takeaways. First, arrhythmia burden is high in ambulatory heart failure patients who have recently had a worsening episode. Second, continuous monitoring reveals many events that may be missed by standard follow-up. Third, the presence of arrhythmia is associated with increased hospitalization and heart failure events. Fourth, detection often prompts treatment changes, including device therapy and ablation.
However, the study does not prove that monitoring itself improves outcomes. It shows association, not necessarily causation. Patients with more arrhythmias may simply be sicker overall. Also, because arrhythmia data were visible to investigators in both arms, the trial was not designed to isolate the effect of rhythm surveillance alone. The main congestion-management intervention did not change arrhythmia burden, so congestion-focused remote management should not be assumed to prevent rhythm problems.
How This Fits Into Heart Failure Care
For clinicians, these findings reinforce the need to think broadly about triggers of heart failure worsening. Fluid overload is only one piece of the puzzle. Arrhythmias can be both a consequence and a driver of worsening heart failure. In many patients, especially older adults with multiple comorbidities, symptoms such as fatigue or shortness of breath may reflect a combination of congestion, atrial fibrillation, bradycardia, ischemia, or ventricular ectopy.
Continuous monitoring may be especially helpful in patients with recurrent unexplained symptoms, recent heart failure hospitalization, or concern for intermittent rhythm disturbances. But monitoring must be paired with a clear management plan to avoid unnecessary procedures and ensure that clinically meaningful findings are addressed promptly.
Limitations
As with any clinical trial, there are limitations to consider. The study population was older and had a high burden of comorbidity, so results may not apply to all heart failure patients. Arrhythmia definitions and detection thresholds are important, because not every recorded episode has the same clinical significance. In addition, outcomes were influenced by clinician-directed management, which may vary across practice settings.
The trial also does not establish whether more aggressive rhythm control, earlier ablation, or device implantation would improve survival or reduce hospitalizations in all patients. Those questions require additional trials.
Practical Takeaway
In patients with symptomatic heart failure and a recent worsening event, arrhythmias are common, clinically relevant, and often actionable. Continuous ICM monitoring identified a substantial burden of atrial fibrillation, bradyarrhythmia, and ventricular tachyarrhythmia, and these findings were linked to later interventions and worse outcomes. The study did not show that a congestion-management strategy changed arrhythmia burden, but it did highlight the value of rhythm surveillance in a high-risk heart failure population.
For patients and clinicians, the message is straightforward: when heart failure worsens, it is important to look beyond fluid status alone. Rhythm assessment can uncover treatable problems that may influence symptoms, hospitalizations, and overall care planning.
Study Reference
Kahwash R, Butler J, Khan MS, Zhang D, Dukes J, Reddy M, Kaplan RM, Amin A, Kanwar R, Sarkar S, Laager V, Wehking J, Van Dorn B, Gerritse B, Patel N, Laechelt A, Zile MR, ALLEVIATE-HF Investigators. Arrhythmia Burden and Clinical Responses Under Continuous Monitoring in Heart Failure: Observations From the ALLEVIATE-HF Trial. Journal of the American College of Cardiology. 2026-05-27. PMID: 42201276.
Trial Registration
Algorithm Using LINQ Sensors for Evaluation And Treatment of Heart Failure (ALLEVIATE-HF); NCT04452149.
