Background: Despite the advancement of electrocardiogram (ECG) monitoring methods, the most important factor influencing diagnostic yield (DY) may still be monitoring duration. Ambulatory ECG monitoring, typically with 24-48 hours duration, is widely used but may result in underdiagnosis of rare arrhythmias.Aims: This study aimed to examine the relationship between the DY and monitoring duration in a large patient cohort and investigate sex and age differences in the presentation of arrhythmias. Methods:The study population consisted of 25 151 patients (57.8% women; median [interquartile range, IQR], 71 [64-78] years), who were examined with mobile cardiac telemetry during 2017 in the United States, using the PocketECG TM that continuously transmits a signal on a beat-to-beat basis. We investigated the occurrence of atrial fibrillation at a burden of both ≤1% (atrial fibrillation [AF], ≤1%) and ≤10% (AF ≤10%), premature ventricular contractions (PVC; >10 000 per 24 hours), non-sustained ventricular tachycardias (nsVT), sustained ventricular tachycardias (VT ≥30 seconds), atrioventricular blocks (AVB), pauses of >3 seconds duration, and bradycardia (heart rate <40 beats per minute for ≥60 seconds). Results:The median (IQR) recording duration was 15.4, 8.2-28.2) days. The DY increased gradually with monitoring duration for all types of investigated arrhythmias. Compared to DY after up to 30 days of monitoring, a standard 24 hours monitoring resulted in DY for males/females of 20%/18% for AF ≤1%, 29%/28% for AF ≤10%, 45%/40% for PVCs, 17%/11% for nsVT, 17%/11% for VT ≥30 seconds, 49%/42 for AVB, 27%/20% for pauses, 36%/29% for bradycardia. Conclusion:A substantial number of patients suffering from arrhythmias may remain undiagnosed due to insufficient ECG monitoring time.

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Introduction: Prior studies have reported sex differences in symptoms and quality of life in patients (pts) with atrial fibrillation (AF). It is currently unclear if this is also true for other arrhythmias or if symptoms occurring at the time of arrhythmia recordings differ by sex. Hypothesis: We hypothesized that women may be more symptomatic than men during atrial and ventricular arrhythmias and that differences may be associated with differences in heart rate (HR). Methods: We examined 27,203 pts (58% women) with up to 30-day ECGs recorded using the PocketECG (MediLynx), which transmits a 3-lead ambulatory ECG and uses an algorithm based on rhythm and morphology. VT and SVT were defined as 3 or more beats, and AV block included 2nd- or 3rd-degree block. A sustained arrhythmia was ≥30s. The rhythm occurring 30 s prior to symptoms was analyzed. Chi2 tests were used to compare women to men. Results: Men were older than women (68.9 ± 13.9 vs 67.7 ±15.6, 95% CI of the difference: [-1.55; -0.84]). Mean HR in SR was faster in women than in men (73.1 ± 10.3 vs. 70.2 ± 10.3 bpm, [2.64; 3.16]). Women were more likely to have SVT (76 vs. 74%) and less likely to have AF (15% vs. 21%), VT (23% vs. 41%), PVCs (45% vs. 61%), PACs (55% vs. 57%) or AV block (21% vs. 28%). Women were more likely than men to report symptoms (66.4% vs. 55.6%, p<0.001), including greater frequency of palpitations, chest discomfort, and shortness of breath (p<0.001 for all). (Figure 1) Women were more likely to report symptoms during PACs and SVT while men were more likely to report symptoms during AF (p <0.001 for all). Mean HR in AF is faster in women (106.5 ± 26.6 vs. 98.7 ± 27.4, 95% CI: [6.29 ; 9.36]). (Figure 2) Conclusions: Symptoms experienced during arrhythmias differ by sex. Reasons for these differences are currently unclear but could be related to ventricular function, underlying heart disease or medications, and are not clearly related to HR. Further study is needed to help identify reasons for differences in symptoms.

Background Frequent premature atrial contractions (PACs) are associated with substantially increased risk of atrial fibrillation (AF) and stroke, but PAC count varies substantially day-to-day. With the emergence of potential therapies for primary prevention of AF reliable estimation of PAC frequency is increasingly relevant, as is an understanding of PAC determinants. Purpose To determine the effect of daily activity and heart rate on an individuals' daily PAC count. Methods We included a random sample of patients 18–85 years without AF who recorded an ambulatory ECG for 7–31 days in the U.S.A during 2019 using a full-disclosure mobile cardiac telemetry device, and who had ≥500PACs on at least one recording day. PACs were algorithmically detected and manually verified. PAC count and activity was sampled for each individual and each recording day during daytime (06–22h). The effect of activity on daily PAC count was assessed in a negative binomial regression model including age, sex and with a random effect for individual, to account for confounding due to inter-individual differences. Results The study population consisted of 2,094 patients, of which 48% were men (Fig 1). Mean time spent in activity was 32% (standard deviation (SD 10%) for men and women 31% (SD 10%) for women (Fig 2). The median PAC count was 592 (inter-quartile range 1280). Beyond age, sex and intra-individual differences PAC frequency was determined by activity levels, (intercept 629 PACs; incidence rate ratio per 10 minute increase in activity 1.03, p&lt;0.0001). A 1-hour increase in daily activity was associated with a 20% increase in daily PACs count. Conclusions Physical activity is associated with increased PACs counts, implying both that a reliable diagnosis of PAC frequency needs to be conducted during a person's habitual level of activity and that PAC frequency is modifiable. In-hospital assessments of PACs while patients are mainly inactive may underestimate PAC frequency. FUNDunding Acknowledgement Type of funding sources: Foundation. Main funding source(s): the Swedish Society For Medical Researchthe Swedish Heart and Lung Foundation Age and sex distribution Activity levels by sex