Assessment of arrhythmias in healthy cats using 24-hour Holter monitoring: a cross-sectional study

Abstract

Background

The objective of this study is to investigate heart rate variables and evaluate the prevalence and characteristics of ventricular premature complexes (VPCs) and supraventricular premature complexes (SPCs) in healthy cats, using 24-hour Holter monitoring in the home environment.

Animals, materials and methods

Thirty-five healthy, client-owned cats were enrolled and divided into two groups: Group 1 included cats aged < 7 years, and Group 2 included cats aged 7 years and older. Clinical examination, blood pressure measurement, total thyroxine levels, echocardiographic assessment and 24-hour Holter monitoring were performed for each cat.

Results

The average minimum (HRmin), mean (HRmean), and maximum heart rate (HRmax) were 103 ± 16.1 bpm, 151 ± 20.2 bpm, and 244 ± 22.6 bpm, respectively. Only HRmin differed between age groups (P = 0.027). Although the percentage of cats with VPCs was similar across groups (75% in Group 1 vs. 91% in Group 2, P = 0.391), older individuals had significantly more VPCs (median 13 vs. 3, P = 0.020), and a higher prevalence of complex arrhythmias (55% vs. 12%, P = 0.014). Older age (P = 0.009), male sex (P = 0.026) and lower body weight (P = 0.049) were significant predictors of the occurrence of VPCs, as well as daytime vs. nighttime (P = 0.013). The number of SPCs was similar in both groups (median and range- 0.5 [0–13] vs. 1 [0–31], P = 0.299).

Study limitations

A small sample size, unevenly distributed between age groups; uneven distribution of cat breeds; analysis of Holter data was made by a single operator; first period of the recording was not excluded from the analysis.

Conclusions

Ventricular arrhythmias are common in healthy cats, and their prevalence and complexity increase with age. Age, sex and weight are significant predictors of the occurrence of VPCs, and VPCs tend to appear more during the day.

Introduction

Over the past decades, ambulatory electrocardiography (Holter monitoring) has been widely used as a non-invasive clinical tool for diagnosing and monitoring cardiac arrhythmias and for risk stratification in humans [1, 2]. Holter monitors typically record three or more electrocardiographic leads continuously for 24–48 h, although extended monitoring for up to two weeks may be performed in certain cases [1].

The results were partially presented as an oral abstract at the 35th Congress of the European Society of Veterinary Internal Medicine- Companion Animals, Maastricht, The Netherlands, 18th-20th September 2025 1.

In veterinary medicine, Holter monitoring is commonly used for the early diagnosis of cardiomyopathies in dogs, including dilated cardiomyopathy in Doberman Pinchers and arrhythmogenic right ventricular cardiomyopathy in Boxers [3, 4]. The prevalence of VPCs on a 24-hour Holter recording can be used to diagnose the occult forms of cardiomyopathy, even before echocardiographic changes can be observed [4, 5].

However, in feline patients, Holter monitoring is not routinely used to assess cardiac disease. The number of studies investigating rhythm disturbances in cats with cardiac disease [6–10] and healthy cats [11–13] remains limited. Given that a routine 5-minute resting electrocardiogram (ECG) represents merely 0.3% of a full 24-hour cycle, its sensitivity for detecting intermittent arrhythmias is limited [13]. Holter monitoring, by enabling continuous long-term electrocardiographic recording, substantially improves the diagnostic efficacy for detecting cardiac rhythm abnormalities [14].

The present study aims to describe 24-hour Holter monitoring findings in healthy unsedated adult cats in the home environment, with a focus on heart rate and the prevalence and characterization of arrhythmias, in order to establish a reference point for comparison in cats with cardiac disease.

Animals, materials & methods

Animals

This cross-sectional study included cats owned by university staff and students. Signalment data, including age, body weight, breed, and sex, were recorded. A complete medical history was obtained, including any previous or current illnesses and ongoing medications. None of the cats included in the study were sedated for the examinations.

Cats were eligible for inclusion in the study if they were at least one year old, had an unremarkable history and physical examination, had a systolic blood pressure below 160 mmHg (measured with a Doppler device, according to the recommendations of the ACVIM consensus statement) [15], were euthyroid (total thyroxine levels < 3.5 µg/dL) [16], and had an echocardiographic assessment that showed no indications of acquired or congenital cardiac disease. The presence of dynamic right ventricular outflow tract obstruction or the presence of an innocent murmur were not considered exclusion criteria. Cats that had a history of chronic disease and cats that received any medication were excluded.

Echocardiography

A complete transthoracic echocardiographic evaluation was performed for each cat using a dedicated ultrasound unit2, which was equipped with a phased array probe appropriate for cats (5–13 MHz), alongside continuous ECG monitoring. The cats were gently manually restrained in both right and left lateral recumbency. Echocardiographic assessment was performed using standard views in two-dimensional, M-mode, color and spectral Doppler modes, following the standard-of-care protocol outlined in the ACVIM consensus statement [17]. Normal ventricular wall thickness was defined by the absence of either segmental or generalized end-diastolic thickening involving the left ventricular posterior wall or the interventricular septum. Specifically, the cut-off value for normality, measured on two-dimensional images obtained from the right parasternal short-axis and long-axis views, was 5 mm. Measurements were performed using the leading edge–to–leading edge technique for the interventricular septum and the left ventricular free wall [17]. Additionally, the craniocaudal dimension of the left atrium was considered normal when it was less than 16 mm [18]. Each parameter was assessed using the average of three measurements to ensure accuracy.

Electrocardiography and Holter monitoring

For each cat, a continuous 5- minute resting 6-lead ECG was recorded in right lateral recumbency following the echocardiographic examination. The ECG was performed using a digital device3.

All Holter4 recordings were conducted while the cats remained in their home environment. Four pre-gelled adhesive electrodes were used, and 3 leads were recorded. Two electrodes were positioned on the right and two on the left side of the thorax after appropriate site preparation, which included shaving the fur and cleaning the skin with surgical alcohol. The electrodes, together with the Holter device, were secured with a cohesive bandage. The recorded data were processed with dedicated software and subsequently reviewed manually by a single operator to identify and correct any errors or misclassified cardiac complexes. The manual review included two separate analyses, with the second one being blinded. The HR (average, minimum, and maximum) was calculated by the software (and manually checked) and expressed as a 10 s average based on the following formula:

Sinus arrhythmia was defined as a rhythm originating from the sinoatrial node, with normal P‑QRS‑T complexes but variable R‑R intervals [19].

Statistical analysis

Statistical analysis was performed using a commercially available statistical software5. Data distribution was tested for normality using the Shapiro-Wilk test.

For variables with a normal distribution, group comparisons were performed using the independent samples t- test. For variables with a non-normal distribution, non-parametric tests, such as Fisher’s exact test for categorical data and the Mann–Whitney U test for continuous data, were applied. Negative binomial regression was used to model associations between predictors and count data. Correlation analyses were conducted using Spearman’s rank correlation coefficient, Pearson’s correlation coefficient, and point- biserial correlation (to analyse the relationship between binary and continuous variables). The association between two categorical variables was analysed using Chi-square test (specifically, the correlation between sinus arrhythmia and sex). The Wilcoxon signed rank test was used to compare the prevalence of VPCs between day and night.

The results for normally distributed data are expressed as the mean ± standard deviation (SD), and the results for non-normally distributed data are presented as the median and range. A statistically significant level of P < 0.05 was considered.

Results

The study included a total of 35 cats, with 18 females and 17 males. The cats were divided into two groups according to their age: the first group consisted of 24 cats under 7 years old (aged 1–6 years, with a mean age of 3.5 ± 1.7 years), and the second group included 11 cats aged 7 years and older (7–15 years, with a mean age of 10 ± 2.8 years). Group 1 included 13 males and 11 females, all of which were neutered, with an average weight of 4.6 ± 0.8 kg. This group consisted of one exotic shorthair, one sphynx, and 22 European shorthair cats. Group 2 included four males and seven females, all of which were neutered, with an average weight of 4.3 ± 1.0 kg. All cats in this group were European shorthair.

Three-lead ECG Holter recordings were obtained for all 35 cats. The median percentage of artefacts was 1.42%, ranging from 0.06% to 11.87%. According to their owners, all the cats tolerated the Holter monitor, with the majority maintaining normal activity levels; only one cat was reportedly reluctant to move while wearing the device. The mean duration of the Holter recordings was 23 h 24 min ± 2 h 27min. The main rhythm identified in all cats was sinus rhythm.

The heart rate variables for the entire population, as well as for the subgroups stratified by age and sex, are summarized in Table 1. Fig. 1 shows the hourly distributions of HRmin, HRmean, and HRmax in the 35 cats. There was a significant difference between the two age groups for HRmin (P = 0.027), with older cats showing higher HRmin but not for HRmean (P = 0.293) or HRmax (P = 0.371). There was no difference in HRmin, HRmax, or HRmean between males and females (P = 0.668, P = 0.933, P = 0.800 respectively).

Table 1.

Heart rate characteristics for the study population

			Range (bpm)	Mean	SD
Entire study group	HRmin		70–154	103	16.1
	HRmean		111–207	151	20.2
	HRmax		199–291	244	22.6
Sex	HRmin	M	70–128	104	17.5
		F	74–154	102	17.5
	HRmean	M	116–178	150	16.8
		F	111–207	151	23.3
	HRmax	M	199–283	245	21.6
		F	203–291	242	21.1
Age group	HRmin	1	70–119	99*	12.4
		2	78–154	111*	20.2
	HRmean	1	111–178	148	18.2
		2	123–207	156	24.1
	HRmax	1	199–291	246	23.6
		2	203–267	238	20.4

bpm Beats per minute, HRmin Minimum heart rate, HRmean Mean heart rate, HRmax Maximum heart rate, SD Standard deviation

1- cats younger than 7 years old

2- cats 7 years & older

^*Statistical difference for HRmin between the 2 age groups (P = 0.027)

Fig. 1.

Average hourly distribution in heart rate metrics over a 24-hour period for the study population

A total of 20/35 cats (57%) showed periods of sinus arrhythmia (SA) during the recording period (Fig. 2). When the cats were divided into two age groups, 16 of 24 cats (67%) aged < 7 years and 4 of 11 cats (36%) aged ≥ 7 years exhibited periods of sinus arrhythmia (SA). There was no statistically significant difference in the proportion of cats displaying sinus arrhythmia between the two age groups (P = 0.144). Sinus arrhythmia was moderately and negatively correlated with HRmin (r_s = − 0.37, P = 0.028) but was not associated with HRmean or HRmax. Cats exhibiting SA had lower HRmin values (P = 0.028) (Fig. 3). However, no differences were found in HRmean or HRmax between the two groups. The presence of sinus arrhythmia is not correlated with sex or weight.

Fig. 2.

Sinus arrhythmia in a 4-year-old male cat, ESH

Fig. 3.

Minimum heart rate between cats with and without sinus arrhythmia. Cats without sinus arrhythmia have a higher median HRmin and a broader interquartile range, whereas those with sinus arrhythmia have a lower median HRmin and a narrower interquartile rang

Ventricular premature complexes (VPCs) were observed in 18 of 24 cats (75%) in the younger age group and 10 of 11 cats (91%) in the older age group. There was no statistically significant difference in the proportion of cats with VPCs between the two age groups (P = 0.391). The median number of VPCs was 3 [0–56] in cats under 7 years old and 13 [0–58] in cats older than 7 years old (Fig. 4). Older cats showed more VPCs than younger ones (P = 0.020), and there was a weak positive correlation between age and the number of VPCs (r_s= 0.34, P = 0.043). Ventricular arrhythmias exhibited both right and left ventricular morphologies. Complex arrhythmias, including couplets, triplets, bigeminy, and episodes of ventricular tachycardia (Fig. 5), were also observed in 3 of 24 cats (12%) in the younger group and in 6 of 11 cats (55%) in the older group (Table 2). The proportion of cats with complex arrhythmias was significantly higher in the older age group (P = 0.014). These findings suggest that age may be associated with the occurrence of complex arrhythmias. The number of VPCs was not significantly correlated with HRmin (P = 0.415), HRmean (P = 0.134), or HRmax (P = 0.880).

Fig. 4.

Prevalence of ventricular premature complexes across the two age groups. Group 2 exhibited a higher median VPCs count and broader interquartile range

Fig. 5.

Types of ventricular arrhythmias observed in the study population. a- couplet; b- bigeminy; c- ventricular tachycardia

Table 2.

Distribution of complex cardiac arrhythmias in the study population

Cat	Group	VPCs/24 h	Couplets	Triplets	Bigeminy	Vtach
1	1	3	1
2	1	21	1	1
3	1	12			1
4	2	14	2
5	2	29	3	2
6	2	58	11	4	1
7	2	49	2	1		1 (4 beats 225 bpm)
8	2	4	1
9	2	11	1

This table includes the cats that showed complex arrhythmias; the number in the table represents the number of events

VPCs Ventricular premature complexes, Vtach Ventricular tachycardia

Negative binomial regression revealed that age was a significant predictor of ventricular arrhythmias, with the number of VPCs increasing with age (P = 0.009). Sex was also a significant predictor, as female cats exhibited fewer VPCs compared to males (P = 0.026). Additionally, higher body weight was associated with fewer VPCs (P = 0.049). Although the median number of VPCs was identical during the day and night (median 2 [0–44] vs. 2 [0–47]), a Wilcoxon signed-rank test demonstrated a statistically significant difference in their distribution (P = 0.013), suggesting that VPCs occur more frequently during the daytime.

Supraventricular premature complexes were found in 12/24 (50%) younger cats and 8/11 (73%) older cats. There was no significant difference in the proportion of cats with SPCs between the two groups (P = 0.281). The median number of SPCs was 0.5 [0–13] in the first age group and 1 [0–31] in the second age group, and there was no statistical difference between the 2 groups (P = 0.299). There was also a weak positive correlation between age and the number of SPCs (r_s= 0.34, P = 0.046).

Both age and weight were significant predictors of the occurrence of SPCs (P = 0.002 and P = 0.011, respectively). The number of SPCs seems to increase as age and weight increase. Sex was not a significant predictor of the occurrence of SPCs (P = 0.702).

Discussion

This study demonstrates that Holter monitoring is an effective method for evaluating arrhythmias in feline patients, enabling the acquisition of high-quality 24-hour ECG recordings in a home setting. These findings underscore the potential of continuous 24-hour ECG monitoring in the management of cardiac disease, particularly considering the higher prevalence of arrhythmias observed in cats with hypertrophic cardiomyopathy [6, 7]. To the authors’ knowledge, this study includes the largest number of healthy cats analysed in this type of research.

In the overall study population, HRmean was 151 ± 20.2 bpm, HRmin was 103 ± 16.1 bpm, and HRmax was 244 ± 22.6 bpm. Among these variables, only HRmin was significantly different between the age groups. Since all the animals in the study were neutered, comparisons between intact and neutered cats were not conducted. The influence of age and sex on HR variables has been reported inconsistently across studies [11–13]. These differences highlight the need for further investigation into sex-related influences on HR variables in cats. Although cats are generally considered nocturnal animals, their activity patterns in domestic settings often adapt to owners’ schedules. In our study, the highest HR values were observed between 12:00 p.m. and 8:00 p.m., which does not align with a nocturnal behaviour, and could reflect periods of interaction or feeding. A direct correlation between activity and HR could not be analysed due to incomplete owner-reported data and difficulties in monitoring nighttime behaviour.

Sinus arrhythmia was common in cats from both age groups; this finding is similar to those of previous studies [11–13, 20]. This study revealed that the presence of SA is moderately and inversely correlated with the average HRmin, which is expected. However, it appears that sinus arrhythmia is not influenced by age or sex. To the authors’ knowledge, the correlation between SA and variables such as age and sex has not been assessed in similar studies.

This study demonstrates that VPCs and SPCs are common in cats from both age groups and that older cats have significantly more VPCs with a higher prevalence of complex arrhythmias. VPCs appeared in 80% of the entire study group; this percentage is similar to that reported in previous studies conducted in healthy cats [11, 12]. It appears that VPCs are also observed in 69% of people [21] and 32% of dogs [22]. In people, certain factors are considered predictors of the appearance of VPCs, such as older age, male sex, higher heart rates and taller height [21]. In this study, older age, lower body weight and male sex appeared to be significant predictors of the presence of VPCs.

In this study, VPCs were more frequently observed during the day. This pattern aligns with existing knowledge that ventricular arrhythmias are modulated by autonomic nervous system activity. Increased sympathetic tone enhances automaticity in pacemaker cells within both the atria and ventricles, whereas the autonomic nervous system also influences triggered activity, promoting the development of early and delayed afterdepolarizations [23]. In humans, sympathetic surges, such as those occurring during exercise or emotional stress, are well-documented triggers for ventricular arrhythmias [24]. Nevertheless, a direct link between elevated daytime sympathetic activity and the development of ventricular arrhythmias in cats has not been elucidated.

In dogs, Holter monitoring is routinely used for the early diagnosis and management of certain cardiomyopathies, such as dilated cardiomyopathy and arrhythmogenic right ventricular cardiomyopathy [3, 4]. However, in feline patients, ambulatory ECG is not routinely employed for the diagnosis of hypertrophic cardiomyopathy or other forms of cardiomyopathy. Establishing clear and comprehensive data on the prevalence and characterization of arrhythmias in healthy cats is essential for improving our understanding of the relationship between arrhythmias and various cardiomyopathies.

Notably, none of the cats presented with arrhythmias during a standard 5-minute ECG performed in the clinic. This emphasizes the value of ambulatory ECG monitoring for detecting such events. It has been previously demonstrated that in-clinic ECG is an insensitive test for detecting ventricular arrhythmias, and the sensitivity of this method may be higher only when the prevalence of VPCs increases [14].

Conclusion

In conclusion, 24-hour Holter monitoring is a valuable tool for assessing cardiac rhythm in cats. Ventricular and supraventricular premature complexes are commonly detected in healthy individuals, with older cats exhibiting a higher frequency and complexity of VPCs. Significant predictors for the occurrence of VPCs include older age, male sex, and lower body weight, and more VPCs tend to appear during the day. Additionally, SA is prevalent among feline patients and appears to be correlated with HRmin.

Limitations

This study has certain limitations. Total thyroxine data were unavailable for 3 cats. As a result, there is a possibility that underlying thyroid abnormalities in these individuals cannot be completely ruled out. Furthermore, the sample size was quite small and not evenly distributed between the two age groups. Cat breeds were also unevenly represented between the two age groups. In addition, Holter recordings analysis was performed by a single operator. The initial Holter recording period was included in the analysis; however, transportation to the cat’s environment and initial acclimation stress may have influenced heart rate and arrhythmia frequency.

Abbreviations

bpm

Beats per minute

ECG

Electrocardiogram

HR

Heart rate

HRmax

Maximum heart rate

HRmean

Mean heart rate

HRmin

Minimum heart rate

SA

Sinus arrhythmia

SPCs

Supraventricular premature complexes

VPCs

Ventricular premature complexes

Authors’ contributions

Conceptualization & Methodology: A.C. and I.C.S.; Investigation: A.C. and R.M.; Formal analysis: A.C.; Writing - Original Draft: A.C. and R.M.; Writing - Review & Editing: I.C.S.; Visualization: A.C. and R.M.; Supervision: I.C.S.

Funding

Not applicable.

Data availability

The datasets used and/or analysed during the current study are available from the corresponding author on reasonable request.

Declarations

Ethics approval and consent to participate

All owners provided informed consent for their cats’ participation. The study was approved by the University of Agricultural Sciences and Veterinary Medicine of Cluj-Napoca Ethics Committee, Subcommittee for the Bioethics of Experiments on Animals, Plants, Food, or Human Subjects (Approval number 491/25.02.2025).

Consent for publication

Not applicable.

Competing interests

The authors declare no competing interests.