Nonsustained ventricular tachycardia (NSVT), defined as ≥3 consecutive ventricular beats at ≥120 beats/min lasting <30 seconds, is an independent predictor of sudden cardiac death (SCD) in hypertrophic cardiomyopathy (HC). Current guidelines recommend 24- to 48-hour Holter monitoring as part of SCD risk stratification. We sought to assess the difference in diagnostic yield of 14-day Holter monitoring compared to 24-48 hours for the detection of NSVT and to assess the prevalence and characteristics of NSVT in patients with HC with prolonged monitoring. We retrospectively analyzed the 14-day Holter monitors of 77 patients with HC from May 2014 to March 2016. Number of episodes and maximal length and rate on each day were recorded. NSVT was detected in 75.3% of patients during 14-day Holter monitoring. The median number of runs was 2 (range 0 to 26 runs). The median number of beats of the longest run was 10.5 (range 3 to 68 beats) with a mean maximum rate of 159.5 ± 20.8.4 beats/min (range 102 to 203 beats/min). First episodes of NSVT were detected throughout the 14 days, with only 22.5% and 44.8% of the episodes captured within the first 24 and 48 hours of monitoring, respectively. In conclusion, prolonged Holter monitoring revealed ≥1 episode of NSVT in 75% of patients with HC of which <50% were detected within the first 48 hours. Hence, prolonged Holter monitoring may be superior for SCD risk stratification in HC. However, the high prevalence of NSVT in this population may limit its utility in evaluating the risk for SCD of the individual patient.
Nonsustained ventricular tachycardia (NSVT), defined as ≥3 consecutive ventricular beats at ≥120 beats/min lasting <30 seconds, is seen in up to 30% of patients with hypertrophic cardiomyopathy (HC) and up to 80% of patients with HC with a history of cardiac arrest during 24- to 48-hour electrocardiography (Holter) monitoring. NSVT has been shown to be an independent predictor of sudden cardiac death (SCD) in HC, particularly in those patients aged <30 years. Thus, the current American College of Cardiology Foundation/American Heart Association (ACCF/AHA) and the European Society of Cardiology (ESC) guidelines recommend 24- to 48-hour Holter monitoring as part of the initial risk stratification for SCD and thereafter every 12 to 24 months. However, the sensitivity of 24- to 48-hour monitoring for detecting NSVT is unknown. Furthermore, scarce data exist on the prevalence of NSVT in patients with HC with prolonged Holter monitoring. Thus, in this study, we sought to assess the difference in diagnostic yield of 14-day Holter monitoring as compared with 24 to 48 hours for the detection of NSVT and the prevalence and characteristics of NSVT in HC with prolonged monitoring.
Methods
We retrospectively analyzed the 14-day Holter monitors of all patients with HC undergoing 14-day Holter monitoring at Toronto General Hospital from May 2014 to March 2016. We documented the number of NSVT and the duration and rate of the longest and fastest episodes on each day. NSVT was defined as ≥3 consecutive ventricular beats at a rate of ≥120 beats/min, lasting for <30 seconds. Patients underwent a 14-day Holter monitor either for risk stratification for SCD mainly in cases where the risk was believed to be intermediate and a decision regarding an implantable cardioverter defibrillator (ICD) implantation had not been made yet or for the evaluation of atrial fibrillation (AF). Patients were considered as having an intermediate risk for SCD if they had a single conventional risk factor, a risk modifier (such as severe late gadolinium enhancement [LGE] on cardiac magnetic resonance imaging [CMR] and/or apical aneurysm), and no conventional risk factors or maximal wall thickness approaching 30 mm (25 to 29 mm).
We compared the detection rate of NSVT as defined by various durations and rates within the first 24 and 48 hours versus the 14-day Holter monitoring. A detailed review of the patients’ charts was carried out.
A group of 55 consecutive patients who underwent 14-day Holter monitoring for the investigation of stroke at The Toronto General Hospital during the same period were used as controls.
The diagnosis of HC was based on echocardiographic findings of septal hypertrophy (≥15 mm) and/or septal or posterior wall thickness ratio >1.3, in the absence of any other cause that could account for the degree of hypertrophy detected.
The extent of LGE on CMR was assessed using a semiquantitative score based on the standard left ventricular 17-segment model and graded as mild (<5%), moderate (5% to 15%), and severe (>15%).
The study was approved by the ethics committee of the Toronto General Hospital.
Data are presented as mean ± standard deviation for normally distributed variables and as median (interquartile range [IQR]) for non–normally distributed variables. Continuous variables were compared using the Student t testing or Mann–Whitney testing, as appropriate. Categorical variables were compared using the chi-square statistics or Fisher’s exact testing, as appropriate. Absolute percentage difference and number needed to screen were calculated using the results of the 14-day Holter monitoring as the reference standard.
Results
The study included 77 patients. Table 1 summarizes their baseline characteristics. The median age of the patients was 56 years (range 17 to 84 years).
| Variable | |
|---|---|
| Mean Age, (years) | 53±14 |
| Males | 52 (68%) |
| Family history of SCD | 9 (12%) |
| Syncope | 14 (18%) |
| Abnormal BP response to exercise ∗ | 8 (10%) |
| Maximal wall thickness on echocardiogram, (mm) | 18.4±4.8 |
| Maximal wall thickness on CMR, (mm) † | 19.8±5.1 |
| NYHA I/II/III/IV | 58 (75%)/13 (17%)/6 (8%)/0 |
| LGE none/mild/moderate/severe † | 10(15%)/22 (29%)/19 (25%)/18 (23%) |
| Hypertension | 23 (30%) |
| Diabetes mellitus | 12 (15%) |
| Coronary artery disease | 5(6%) |
| Dyslipidemia | 26 (34%) |
| Smoker | 6 (8%) |
| Atrial fibrillation | 13 (17%) |
| Cerebrovascular accident | 5 (6%) |
| Obstructive/Apical | 27 (35%) /15 (20%) |
| Apical left ventricular aneurysm | 9 (12%) |
| Previous septal reduction procedure | 11 (14%) |
| Genetic status: negative/MYH7/MYBPC3/no genetic testing | 33 (43%)/ 12 (16%)/ 8(10%) / 22(29%) |
| Medications | |
| Beta blocker | 55(71%) |
| Non dihydropyridine calcium channel blocker | 5 (7%) |
| Amiodarone | 2 (3%) |
| Disopyramide | 9 (12%) |
∗ Considered a risk factor for SCD in patients<50 years of age.
Holter monitoring was performed to detect NSVT for the purpose of risk stratification for SCD and for the detection of AF in 80% and 20% of the patients, respectively. Among those being evaluated for SCD risk, the following were the most common clinical characteristics: severe LGE on CMR (23%), syncope (11%), family history of SCD (10%), maximal wall thickness approaching 30 mm (25 to 29 mm; 10%), slow or infrequent episodes of NSVT on 48-hour Holter monitoring (17%), and apical aneurysm (12%).
Overall, NSVT (as defined by ≥3 beats at ≥120 beats/min) was detected in 75% of patients during 14-day Holter monitoring. The median number of runs of NSVT was 2 (IQR 0.75 to 4 episodes, range 0 to 26). The median number of beats of the longest run of NSVT was 10.5 (IQR 4 to 15 beats, range 3 to 68 beats) with a mean maximum rate of the runs of 159.5 ± 20.8.4 (range 102 to 203) beats/min.
Monitoring the patients with a 14-day Holter was superior to 24- and 48-hour Holter monitoring for the detection of at least 1 episode of NSVT. NSVT was detected in only 16.9% of patients during the first 24 hours (absolute percentage difference of 59%, p <0.0001) and in 34% during the first 48 hours (absolute percentage difference of 42%, p <0.0001; Figure 1 ). First episodes of NSVT were detected throughout the 14 days, with only 23% and 45% of the episodes captured within the first 24 and 48 hours of monitoring, respectively.
Patients exhibiting episodes of NSVT during the first 48 hours of monitoring had a significantly greater number of episodes compared to patients first exhibiting NSVT beyond the first 48 hours (median number of runs of 5 vs 1, p <0.0001). In addition, the median number of beats of the longest run and the mean maximum rate were significantly higher in patients exhibiting NSVT within the first 48 hours of monitoring than those not exhibiting NSVT during the first 48 hours (14 vs 5 beats, p = 0.0021 and 168 vs 153 beats/min, p = 0.004, respectively).
The control group consisted of 55 consecutive patients (56% men, mean age 64.3 ± 17.8 years) who had suffered a stroke or transient ischemic attack and underwent 14-day Holter monitoring as part of the investigations.
The prevalence of NSVT in the control group was significantly lower than in patients with HC (15% vs 75%, p <0.0001). Episodes of NSVT were seen in 8 control patients, where in only 1 of these patients was this seen in the first 48 hours of monitoring.
For the purpose of this study, we arbitrarily considered NSVT of at least 5 beats at a rate of ≥180 beats/min as an indicator of greater arrhythmia risk. Using this definition as a cutoff for NSVT, at least 1 episode was detected in 11% of the patients on 14-day Holter monitoring. However, none were detected during the first 24 hours (p <0.0001) and only 2 during the first 48 hours ( Figure 1 ).
NSVT was significantly more common in male than in female patients (82% vs 56%, p = 0.027). There were no significant differences in age, maximal wall thickness, left ventricular outflow tract gradient, degree of LGE, prevalence of other conventional risk factors for SCD, genetic status, and prevalence of AF between patients exhibiting and not exhibiting NSVT.
The cumulative prevalence of the first episode of NSVT at different rates and lengths during the 14-day monitoring is depicted in Figure 2 . It can be seen that as the NSVT was more prolonged or faster, the detection rate within the first 48 hours of monitoring decreased, such that 49% of NSVT ≥5 beats were detected first during the initial 48 hours compared to only 17.6% of NSVT ≥15 beats and 37% of NSVT ≥150 beats/min versus only 16.6% of NSVT ≥180 beats/min. Figure 3 shows the 14-day Holter monitoring tracing of a patient whose first episode of NSVT (11 beats at 189 beats/min) was detected on the fourth day and had additional episodes of NSVT during the following days.
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