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Introduction Ambulatory electrocardiogram (ECG) monitoring is used to measure the cardiac rhythm of a patient over a continuous period of time to assess for the presence of arrhythmias. This is normally requested for a period of 24 hours, 48 hours, 72 hours, or 7 days. However, there is little guidance about the optimum time to request ambulatory monitoring for particular indications. Most existing research on ambulatory ECG monitoring longer than the 24-hour period are mostly in the paroxysmal atrial fibrillation population to investigate cryptogenic ischaemic stroke. 1–4 There remains a lack of comparison between 48-hour and 72-hour monitoring, especially outside of a stroke population. The aim of our study was to determine how much better a 72-hour ECG is compared with a 48-hour ECG at diagnosing rhythm abnormalities in all patient population, not confining to stroke population alone.Methods This was a single-centre, retrospective study of all 72-hour ECG monitors performed between January 2023 and May 2025 at Royal Surrey County Hospital, Guildford, Surrey.Indication for the 72-hour ECG monitor was recorded based on the Holter form request, categorised as ‘Post stroke’, ‘Palpitations’, ‘Syncope/dizziness/faints/collapse’, ‘Breathlessness’, ‘Chest pain’, ‘Heart Failure’, ‘Hypertension’, ‘Post stroke’, and ‘Other’.Pathology was categorised based on the following arrhythmia categories of ‘Atrial fibrillation/flutter’, ‘Atrial runs>=5 beats’, ‘Ventricular tachycardia >=5 beats’, ‘Atrioventricular block – 2nd degree or higher’, ‘Pause >3s’ and ‘Ventricular ectopic burden >1%’. These categories were informed by previous papers categorising arrhythmias on Holter monitoring.For each ambulatory monitor recording, the first 48 hours of the ECG monitor was reviewed for the presence of arrhythmia pathology, which acted as a paired control for the entire 72-hour ECG monitor recording.Results Baseline Characteristics371 patients were identified as having 72-hour ECG requests between January 2023 and May 2025, of which 281 patients with 72-hour ECG requests were included (figure 1). Patients were excluded if the ECG monitor showed less than 64 hours of recorded activity or if their results were no longer on the system. The age range of patients were between 4-91 (median 64). 41% of patients were male. The majority of patients had ambulatory monitoring performed for palpitations (figure 2).PathologyOut of the 281 patients, 205 patients had a completely normal ambulatory ECG. 71 patients had abnormal ECGs in the first 48 hours, and 76 patients had abnormal tapes in 72 hours (table 1).Interestingly, no rhythm abnormalities were detected in the post-stroke patients. Additional rhythm abnormalities were picked up in the breathlessness, syncope, and palpitations category with 72-hour monitoring.The 11 additional rhythm abnormalities picked up were 2 atrial runs, 3 ventricular tachycardia, 2 atrial fibrillation, 2 nocturnal Mobitz 1, 1 nocturnal Mobitz 2, and 1 ventricular ectopic burden >1% (table 2). There was increased pick-up of atrial fibrillation/flutter (absolute increase of 0.7% of population screened), atrial runs (absolute increase of 1.1%), nocturnal Mobitz 1 (absolute of 0.4%) and nocturnal Mobitz 2 (absolute increase of 0.4%). There was also an increase in ventricular tachycardia detection (absolute increase of 1.1%) in the syncope and palpitations group. There was an increase detection of ventricular ectopic burden >1% of 0.3%. No cases of complete heart block were found in our cohort. 72-hour ECG did not increase the detection of pauses.Conclusion These results demonstrate that there is only a small pick-up rate for rhythm abnormalities by extending the monitoring by 24 hours from 48-hour ECG to 72-hour ECG.References Kwon S, Lee SR, Choi EK, Ahn HJ, Song HS, Lee YS, Oh S, Lip GYH. Comparison between the 24-hour Holter test and 72-hour single-lead electrocardiogram monitoring with an adhesive patch-type device for atrial fibrillation detection: prospective cohort study. J Med Internet Res. 2022 May 9;24(5):e37970. doi: 10.2196/37970. PMID: 35532989; PMCID: PMC9127648.Stahrenberg R, Weber-Krüger M, Seegers J, Edelmann F, Lahno R, Haase B, Mende M, Wohlfahrt J, Kermer P, Vollmann D, Hasenfuss G, Gröschel K, Wachter R. Enhanced detection of paroxysmal atrial fibrillation by early and prolonged continuous holter monitoring in patients with cerebral ischemia presenting in sinus rhythm. Stroke. 2010 Dec;41(12):2884–8. doi: 10.1161/STROKEAHA.110.591958. Epub 2010 Oct 21. PMID: 20966415.Kułach A, Dewerenda M, Majewski M, Lasek-Bal A, Gąsior Z. 72 hour Holter monitoring, 7 day Holter monitoring, and 30 day intermittent patient-activated heart rhythm recording in detecting arrhythmias in cryptogenic stroke patients free from arrhythmia in a screening 24 h Holter. Open Med (Wars). 2020 Jul 18;15(1):697–701. doi: 10.1515/med-2020-0203. PMID: 33336026; PMCID: PMC7712313.Chua SK, Chen LC, Lien LM, Lo HM, Liao ZY, Chao SP, Chuang CY, Chiu CZ. Comparison of arrhythmia detection by 24-hour Holter and 14-day continuous electrocardiography patch monitoring. Acta Cardiol Sin. 2020 May;36(3):251–259. doi: 10.6515/ACS.202005_36(3).20190903A. PMID: 32425440; PMCID: PMC7220965.Abstract 426 Figure 1Flow diagram for inclusion and exclusion of patients for studyAbstract 426 Figure 2Indications for 72-hour ECG monitoringAbstract 426 Table 1Pathology found by indication for ambulatory monitoringBy indicationIn 48h abnormal%In 72habnormal%Post stroke (n = 5)00%00%Palpitations (n = 144)3423.6%3620.0%Syncope/Dizziness/Faints/Collapse (n = 65)2030.8%2335.4%Breathlessness (n = 10)220.0%220.0%Chest Pain (n = 14)321.4%321.4%Heart Failure (n = 1)00%00%Other (n = 42)1228.6%1228.6%Abstract 426 Table 2Discrete pathology identified in 48 hours and in 72 hours. Note that some patients had multiple pathologies identifiedDiscrete Pathology foundIn 48h%In 72h%Atrial fibrillation/flutter3010.7%3211.4%Atrial runs >= 5 beats248.5%279.6%Ventricular tachycardia >=5 beats62.1%93.2%2nd degree atrioventricular block - Wenckebach134.6%145.0%2nd degree atrioventricular block - Mobitz type 220.7%31.1%Complete Heart Block00%00%Sinus pause >3s51.8%51.8%Atrial fibrillation pause >3s41.4%41.4%Ventricular ectopic burden >1%103.6%113.9%