Written by: Mihikaa Roy
Edited by: Aleeza H & Jessica R
Atrial Fibrillation
Atrial fibrillation (also known as AFib or AF) is a type of irregular heartbeat or in other words, arrhythmia. It affects the top two chambers of the heart called the atria. In AFib, the electric signals that help push the blood into the ventricles are fast or irregular. As a result, the heart is unable to pump efficiently which can lead to blood clots. The most common complications of AFib are stroke and heart failure if left untreated. Approximately a quarter of all strokes after the age of 40 are caused by AFib, with some common causes including high blood pressure, heart failure, diabetes, and heart disease. The treatment for AFib varies based on the patient but, the two general strategies are rate control and rhythm control. Rate control involves a patient receiving medication to reduce their heart rate. On the other hand, rhythm control is restoring and maintaining a regular heartbeat with medication or, if needed, electrical cardioversion. Electric cardioversion is a procedure that uses controlled electric pulses to maintain a normal heart rhythm.
Introducing the Study
The life expectancy of patients with cancer is increasing as the screening, diagnosis, and treatment of cancer improves. However, the prevalence of cardiovascular disease, particularly in cancer survivors is increasing as well. Thus, atrial fibrillation, the most common arrhythmia, is a major concern among older cancer patients. A study published on June 15, 2021 discussed the possibility of cancer patients having an increased risk of atrial fibrillation. The study was based in South Korea and observed 816,811 cancer patients. 19 different types of cancer were analyzed to see their separate impacts on cardiac health. Previous studies have reported that atrial fibrillation leads to an increased risk of cancer. As such, the validity of these results and the correlation between atrial fibrillation and cancer cannot be concluded for certain, until further more in-depth research is conducted.
Method
To select patients, all patients diagnosed with cancer between January 1, 2009, and December 31, 2016, were chosen from the Korean database. Subjects who had unavailable health examination data from the last two years or missing health data were excluded from the experiment. All of the subjects had two people of a similar age and sex act as their control group. A control group is used to establish stronger correlations between variables as the results of both groups can be compared. If a subject or control group member has any previous history of atrial fibrillation, they were omitted from the study as well.
The subjects were tracked until they were determined to have AFib, their death, or at the end of the study period on December 31, 2017, whichever came first. There were 3 landmarks: 90 days, 1 year, and 5 years after cancer diagnosis - which were used to perform landmark analysis. During this analysis, the survivors thus far were analyzed to confirm the status of their cardiac health. In the case that atrial fibrillation was found, its impact was minimized and its long-term effects were evaluated.
To evaluate, statistical analysis was used to confirm the validity of the data. Then, the incidence of AFib in the patients with cancer was compared with the control group, followed by analyzing the 19 types of cancer separately. As different factors may be impacting the cardiac health of the subjects such as hypertension, obesity, kidney disease, and smoking, a subgroup analysis of those factors was conducted. All of the values were statistically significant. Thus, the experiment did not have any bias from the factors that may affect the possibility of atrial fibrillation.
Results
In the follow-up period, 3.1% of patients in the cancer cohort developed AFib, whereas 1.9% of subjects in the control group were affected. The median time for the AFib to be diagnosed in the cancer cohort was 1.7 years, and 3.2 years in the control group. Therefore, the patients with cancer demonstrated a higher incidence of AFib and a faster onset of the disease than the general population as demonstrated by the control group.
All the types of cancer analyzed led to an increased incidence of AFib; however, the incidence rate varies based on the cancer type. The highest risk of AFib was associated with multiple myeloma and the lowest risk was for patients with stomach cancer. All hematologic malignancies (cancer affecting blood, bone marrow, and lymph nodes) including lymphoma and leukemia, in addition to some solid cancers like lung cancer and esophageal cancer, were associated with a high risk of AFib development.
The study also demonstrated that the association between most types of cancer and the risk of AFib declines with time after being diagnosed with cancer. However, hematologic malignancies, lung, liver, renal, and gynecologic cancers displayed a significant increase in the risk of developing AFib five years after the cancer diagnosis.
Conclusion
The correlation can be explained using many explanations. Cancer therapies like surgery, systematic treatment, and anti-cancer drugs have shown an association with the onset of AFib. One particular example is hematopoietic stem cell transplantation, a common treatment strategy used for hematologic malignancies in patients. Furthermore, inflammation may lead to carcinogenesis and be correlated with developing AFib. Lastly, the association may be caused by an imbalance in the nervous system, paraneoplastic syndromes (rare disorders triggered by an unusual immune system response to cancerous tumors), or a tumor on a cardiac structure.
Although there were limitations to the study such as lack of data pertaining to the stage of cancer, treatment strategy, responsiveness to treatment, and biomarkers, the results were analyzed using several different methods and displayed results that conform with previous studies. Overall, patients with cancer have a higher risk of developing AFib compared with the general population which varies with the type of cancer and should be considered when treating them.
References
ACC News Story. “Study Finds Cancer Increases Risk of AFib, But Varies Depending on Type of Cancer.” American College of Cardiology, 15 June 2021, www.acc.org/latest-in-cardiology/articles/2021/06/15/21/01/study-finds-cancer-increases-risk-of-afib.
“Atrial Fibrillation.” Heart and Stroke Foundation of Canada, 2020, www.heartandstroke.ca/heart-disease/conditions/atrial-fibrillation.
Kayla Matthews, Matthews. “Breast Cancer and Atrial Fibrillation.” Edited by Mary Cooke, News Medical, 10 Apr. 2020, www.news-medical.net/health/Breast-Cancer-and-Atrial-Fibrillation.aspx.
Yun, Jun Pil, et al. “Risk of Atrial Fibrillation According to Cancer Type: A Nationwide Population-Based Study.” JACC, 1 June 2021, www.jacc.org/doi/10.1016/j.jaccao.2021.03.006?_ga=2.160047229.1703214072.1624761392-964786459.1623787546.