Background
Heart failure is a chronic condition in which the heart cannot pump blood as effectively as the body needs. Many patients with heart failure also develop arrhythmias, or abnormal heart rhythms, which can range from atrial fibrillation to dangerous ventricular rhythms and slow heart rates. These rhythm problems may worsen symptoms, trigger hospitalizations, and sometimes lead to sudden clinical deterioration. However, in ambulatory patients with symptomatic heart failure who do not already have a cardiac implantable electronic device, the true burden of arrhythmias has not been well defined.
A related question is whether managing congestion remotely using device-guided strategies can change how often arrhythmias occur. Congestion refers to fluid buildup, often causing swelling, weight gain, and shortness of breath. The ALLEVIATE-HF trial was designed to examine congestion management using an insertable cardiac monitor, or ICM, a small device placed under the skin that continuously records heart rhythm. This report describes the arrhythmia findings from that trial and how they related to treatment decisions and clinical outcomes.
Study Design
ALLEVIATE-HF enrolled patients with New York Heart Association functional class II to III heart failure, meaning they had mild to moderate limitation of physical activity due to symptoms. Patients could have any ejection fraction, which is a measure of how much blood the left ventricle pumps out with each beat. All participants had experienced a recent heart failure event and had no prior cardiac implantable electronic device.
After implantation of the ICM, patients were randomized to one of two approaches: ICM-guided, physician-directed, nurse-facilitated congestion management, or usual care. Importantly, arrhythmia data were visible to investigators in both groups, and any rhythm-related treatment decisions were made by clinicians rather than by a fully automated protocol. This allowed the investigators to evaluate the natural burden of arrhythmias and the actions taken in response to them.
Arrhythmia occurrence was estimated using Kaplan-Meier methods, which track the probability of events over time. The study also used time-varying Cox models to examine whether arrhythmias were linked to later therapeutic interventions or clinical events such as hospitalization.
Patient Population
The analysis included 711 patients. The mean age was 70.5 years, with a standard deviation of 10.4 years, and 45.7% were women. Follow-up averaged 17.3 months. Most patients, 67.9%, had heart failure with preserved ejection fraction, and 60.2% were in NYHA functional class II at baseline. This reflects a real-world population of older adults with symptomatic heart failure, many of whom do not have severely reduced pumping function.
Main Findings: Arrhythmia Burden
During the 13-month randomized phase, the rate of arrhythmia occurrence did not differ between the study arms. In other words, the strategy of ICM-guided congestion management did not appear to reduce or increase arrhythmias compared with usual care. This suggests that while congestion management may affect symptoms and fluid status, it did not materially change the underlying arrhythmia burden during the study period.
Over three years of follow-up, arrhythmias were very common. Overall atrial fibrillation occurred in 66.6% of patients, and 25.4% developed new-onset atrial fibrillation. Bradyarrhythmias, which are abnormally slow heart rhythms, occurred in 47.1% of patients. Ventricular tachycardia or fibrillation, the most concerning fast ventricular rhythms, occurred in 20.1%.
These figures are clinically important because they show that a substantial proportion of patients with symptomatic heart failure harbor rhythm disturbances that may not be fully appreciated without continuous monitoring. Some of these arrhythmias can be silent, intermittent, or detected only after a major event.
Link Between Arrhythmias and Clinical Actions
The ICM findings were strongly associated with subsequent therapeutic actions. When an arrhythmia was recorded by the ICM, the likelihood of an arrhythmia-related intervention increased significantly. Overall, arrhythmia detection was associated with a higher chance of intervention, with a hazard ratio of 3.81.
The associations were particularly strong when specific rhythm types were analyzed:
– Ventricular tachycardia or fibrillation and related interventions: hazard ratio 7.04
– Atrial fibrillation and related interventions: hazard ratio 3.28
– Bradyarrhythmia and related interventions: hazard ratio 7.22
All of these associations were highly significant. In practical terms, this means that once the monitor detected a rhythm abnormality, clinicians were much more likely to respond with treatment changes. These responses may have included medication adjustments, anticoagulation for atrial fibrillation, electrophysiology referral, pacemaker or defibrillator evaluation, or catheter ablation depending on the rhythm and the patient’s condition.
Association With Hospitalization and Heart Failure Events
ICM-recorded arrhythmias were also associated with worse clinical outcomes. Patients with detected arrhythmias 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. These findings support the idea that arrhythmias are not merely incidental findings in heart failure; they often reflect a more unstable clinical state and may contribute directly to symptom worsening and decompensation.
This does not prove that the arrhythmia itself caused every hospitalization, but it strongly suggests that continuous rhythm monitoring can identify patients at higher near-term risk who may need closer follow-up.
Therapeutic Device Implantation and Ablation
During follow-up, therapeutic cardiac implantable electronic device implantation occurred in 22.7% of patients, and catheter ablation occurred in 26.1%. These are substantial proportions and indicate that rhythm findings often led to significant downstream management.
Device implantation may include pacemakers or implantable cardioverter-defibrillators, depending on whether the problem is bradyarrhythmia, malignant ventricular arrhythmia risk, or another indication. Ablation is a procedure that targets abnormal electrical pathways in the heart and is commonly used for atrial fibrillation, atrial flutter, and certain ventricular arrhythmias. The relatively high ablation rate underscores how frequently clinically relevant rhythm disturbances emerged in this population.
Differences by Ejection Fraction
The study also found meaningful differences according to ejection fraction. Bradyarrhythmias were more common in patients with ejection fraction of 50% or higher, which generally corresponds to heart failure with preserved ejection fraction. In contrast, ventricular tachycardia or fibrillation occurred more often in patients with ejection fraction below 50%. Atrial fibrillation occurred at similar rates in both groups.
These patterns are consistent with clinical experience: patients with preserved ejection fraction often have a high burden of comorbidities and conduction system disease, while reduced ejection fraction is more strongly associated with ventricular arrhythmia risk. Nevertheless, atrial fibrillation remained a major problem across the spectrum of heart failure phenotypes.
Clinical Meaning
The main message of ALLEVIATE-HF is that continuous monitoring uncovers a large and clinically meaningful arrhythmia burden in patients with recent symptomatic heart failure events. The burden was not altered by the protocol-driven congestion-management strategy used in the trial, but the monitoring system revealed many rhythm disturbances that were linked to treatment escalation and adverse outcomes.
For clinicians, this supports several practical points. First, arrhythmias should be actively considered in symptomatic heart failure patients even when they do not have a prior device. Second, continuous monitoring may help identify patients who need intervention before their condition worsens. Third, the type of arrhythmia matters: atrial fibrillation, bradyarrhythmia, and ventricular arrhythmias each carry different treatment implications.
For atrial fibrillation, management may include rhythm control, rate control, anticoagulation, or ablation depending on symptoms and stroke risk. For bradyarrhythmias, pacemaker evaluation may be required if slow rhythms are causing symptoms or limiting therapy. For ventricular tachycardia or fibrillation, urgent assessment for defibrillator therapy, antiarrhythmic treatment, or ablation may be needed.
What the Study Does and Does Not Show
This trial provides strong observational insight within a randomized framework, but it does not prove that ICM monitoring itself improves outcomes. The study shows association rather than direct causation between arrhythmias and later interventions or hospitalization. It also reflects practice in a setting where investigators could see arrhythmia data in both groups, which may have influenced care decisions.
Still, the results are highly relevant because they demonstrate that arrhythmias are common, often clinically actionable, and associated with worse outcomes in a heart failure population that might otherwise be under-monitored.
Conclusion
In ambulatory patients with recent symptomatic heart failure, a protocol-driven congestion-management strategy did not change arrhythmia burden during the randomized phase of ALLEVIATE-HF. However, continuous insertable cardiac monitor surveillance revealed a high frequency of atrial fibrillation, bradyarrhythmias, and ventricular tachycardia or fibrillation. These arrhythmias were associated with more therapeutic interventions, more device implantation and ablation, and higher risks of hospitalization and heart failure events.
The findings highlight the value of continuous rhythm monitoring as a tool for identifying clinically important arrhythmias in heart failure and for informing timely management decisions.