Overview
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 slow heart rates and dangerous ventricular rhythms. In daily practice, however, the true burden of arrhythmia in ambulatory patients with symptomatic heart failure has not been fully defined, especially in people who do not already have a cardiac implantable electronic device such as a pacemaker, defibrillator, or cardiac resynchronization device.
The ALLEVIATE-HF trial addressed an important clinical question: if clinicians use continuous insertable cardiac monitor data to guide congestion management in heart failure, does that strategy reduce arrhythmias? The answer from this analysis was no. Arrhythmia burden was not meaningfully different between the randomized management strategies, but continuous monitoring revealed that arrhythmias were very common and often clinically important.
Why arrhythmias matter in heart failure
Arrhythmias are common in heart failure because the failing heart changes in size, pressure, electrical stability, and oxygen balance. These changes can increase the risk of:
Atrial fibrillation, which may worsen symptoms, raise stroke risk, and reduce cardiac efficiency;
Bradyarrhythmias, which can cause fatigue, dizziness, syncope, or worsen low-output symptoms;
Ventricular tachycardia or fibrillation, which may be life-threatening and sometimes lead to sudden cardiac death.
For clinicians, knowing when these rhythms occur can influence treatment decisions such as medication adjustment, anticoagulation, catheter ablation, or implantation of a pacemaker or defibrillator. For patients, arrhythmias may explain worsening breathlessness, palpitations, fainting, or repeated hospital visits.
Study design and monitoring approach
ALLEVIATE-HF enrolled ambulatory patients with New York Heart Association class II to III heart failure, any ejection fraction, and a recent heart failure event. Importantly, the study excluded patients who already had a cardiac implantable electronic device. All participants underwent implantation of an insertable cardiac monitor (ICM), a small device placed under the skin that continuously records heart rhythm over long periods.
Patients were randomized to one of two congestion-management strategies during the 13-month randomized phase:
ICM-guided, physician-directed, nurse-facilitated congestion management;
Usual care.
Even though the management strategy differed, arrhythmia data were available to investigators in both groups, and arrhythmia-related treatment decisions were made by clinicians rather than by a rigid protocol. This design allowed the researchers to observe whether more intensive congestion management changed arrhythmia occurrence and how often detected arrhythmias triggered clinical action.
Key findings
The analysis included 711 patients, with a mean age of 70.5 years and 45.7% women. The average follow-up was 17.3 months. Most patients had heart failure with preserved ejection fraction: 67.9% had an ejection fraction of at least 50%, and 60.2% were in NYHA class II at baseline.
During the randomized phase, the arrhythmia occurrence rate did not differ between the study arms. In other words, the congestion-management strategy guided by ICM data did not reduce or increase the overall burden of arrhythmias compared with usual care.
Over 3 years, the overall occurrence of atrial fibrillation was 66.6%, and new-onset atrial fibrillation occurred in 25.4% of patients. Bradyarrhythmia occurred in 47.1%, and ventricular tachycardia or fibrillation occurred in 20.1%. These rates show that rhythm abnormalities are extremely common in this population, even when patients are being followed closely.
Clinical meaning of the detected arrhythmias
The most important message from this study is not simply that arrhythmias were frequent, but that ICM-detected arrhythmias were strongly linked to later clinical responses and adverse events.
When an arrhythmia was recorded by the monitor, the likelihood of subsequent arrhythmia-related intervention increased substantially. The associations were strong for all major rhythm categories:
Overall arrhythmia and arrhythmia-related intervention: hazard ratio 3.81;
Ventricular tachycardia/fibrillation and related intervention: hazard ratio 7.04;
Atrial fibrillation and related intervention: hazard ratio 3.28;
Bradyarrhythmia and related intervention: hazard ratio 7.22.
All of these associations were highly significant statistically. This suggests that continuous monitoring was not merely detecting irrelevant rhythm changes. Instead, it identified events that often prompted meaningful treatment decisions.
The study also found that ICM-recorded arrhythmia was associated with a higher risk of all-cause hospitalization and heart failure events. Specifically, the hazard ratio was 1.79 for all-cause hospitalization and 1.69 for heart failure events. This does not prove that arrhythmias directly caused the hospitalizations, but it does suggest that arrhythmia detection may be an important marker of overall worsening clinical status.
Therapeutic responses
The study reported substantial downstream interventions after arrhythmia detection. Therapeutic cardiac implantable electronic device implantation occurred in 22.7% of patients, and ablation occurred in 26.1%.
This is clinically relevant because it shows that continuous monitoring can uncover actionable rhythms. For example:
A patient with recurrent bradyarrhythmias may need a pacemaker;
A patient with ventricular tachyarrhythmias may require an implantable cardioverter-defibrillator or further electrophysiologic evaluation;
A patient with atrial fibrillation may need rate or rhythm control, anticoagulation, or ablation.
In modern heart failure care, the monitor is not the treatment itself, but it can identify patients who would benefit from targeted intervention.
Differences by ejection fraction
The study also explored whether arrhythmia patterns differed based on ejection fraction. The findings were clinically intuitive:
Bradyarrhythmias were more common in patients with ejection fraction of at least 50%;
Ventricular tachycardia or fibrillation occurred more frequently in patients with ejection fraction below 50%;
Atrial fibrillation occurred at similar rates in both groups.
This pattern suggests that arrhythmia risk in heart failure is heterogeneous and may reflect different underlying mechanisms depending on cardiac structure and function. Patients with preserved ejection fraction often have older age, hypertension, atrial remodeling, and conduction disease, which may help explain the higher bradyarrhythmia burden. Those with reduced or mildly reduced ejection fraction may have more ventricular electrical instability.
What this means for clinicians
Several practical lessons emerge from ALLEVIATE-HF:
First, arrhythmia burden in symptomatic heart failure is high, even in outpatients without a pre-existing implanted device.
Second, a congestion-management strategy guided by continuous ICM data did not reduce arrhythmia occurrence during the randomized phase.
Third, continuous monitoring identified arrhythmias that were often clinically meaningful and associated with hospitalization, heart failure events, and therapeutic action.
Fourth, the type of arrhythmia differs by ejection fraction, so risk assessment should be individualized.
These findings support the idea that rhythm surveillance can complement symptom-based heart failure follow-up. However, the study does not show that implanting an ICM and using it to guide congestion management alone will reduce arrhythmias. Instead, it highlights the monitor’s role as a detection and decision-support tool.
What this means for patients
For patients with heart failure, this study reinforces the importance of close follow-up and symptom reporting. New palpitations, fainting, unusual fatigue, dizziness, worsening shortness of breath, or sudden swelling may signal an arrhythmia or worsening heart failure.
An insertable monitor may help clinicians find rhythm problems that are otherwise missed, especially when episodes are intermittent. But monitoring is only useful if the findings lead to appropriate treatment, such as medication changes, anticoagulation, ablation, or device therapy when indicated.
Patients should also remember that not every detected arrhythmia requires an invasive procedure. Treatment depends on the rhythm type, frequency, symptoms, heart function, stroke risk, and overall clinical picture.
Study strengths and limitations
This study has several strengths, including a large sample size, prolonged follow-up, continuous rhythm surveillance, and real-world clinical decision-making. These features make the findings highly relevant to everyday heart failure practice.
There are also limitations to consider. Because arrhythmia data were available to investigators in both groups, the study was not blinded in a way that would fully isolate the impact of rhythm knowledge on treatment decisions. In addition, the observed associations between arrhythmias and hospitalizations do not establish direct causation. Patients with more arrhythmias may simply have had more advanced disease overall.
Finally, the study population included a broad heart failure cohort, but results may not apply equally to all patient groups, such as those with advanced device therapy, severe frailty, or different care settings.
Conclusion
In ambulatory patients with recent symptomatic heart failure events, a continuous ICM-guided congestion-management strategy did not alter arrhythmia burden during the randomized phase of ALLEVIATE-HF. Nevertheless, continuous monitoring revealed a very high prevalence of atrial fibrillation, bradyarrhythmias, and ventricular tachycardia or fibrillation. These arrhythmias were strongly associated with clinical interventions, hospitalization, and heart failure events.
The study supports continuous rhythm monitoring as a valuable tool for identifying meaningful electrical instability in heart failure, but it does not suggest that monitoring-guided congestion management alone is enough to reduce arrhythmias. Instead, it underscores the need for individualized rhythm assessment and prompt clinical response when arrhythmias are detected.
