Relationship between episodes of unsustained VTs detected early after an ICD implant and subsequent monomorphic VTs causing appropriate therapy

Introduction

Non-sustained ventricular tachycardias (NSVT) are observed frequently among ICD patients with left ventricular dysfunction (LVD).

Purpose

To analyze the relationship between episodes of NSVTs and monomorphic VTs (MVTs) that subsequently cause appropriate therapies.

Methods

416 ICD patients with LVD (LVEF <45%) followed for 41±27 months. ICD programming (detection and therapies) was standardized. NSVT was defined as any VT of ≥5 beats which did not met the detection criteria occurring within the first 6 months after ICD implant. We analyzed 2201 NSVTs (10+7 beats), which occurred in 250 of the 416 patients (Median=2; IQR=0–7). The mean cycle length (CL) of NSVT was 323±32 ms (adjusted per multiple episodes/patient, generalized estimating equation method (GEEM)).

Results

During the follow-up, 1441 MVT occurred in 183 patients. After showing a significant correlation between burden of NSVT and the occurrence of appropriate therapies due to MVT (C coefficient=0.68; p<0.001), we observed that subjects with >5 NSVT presented an excess of adjusted risk: HR=1.97 (95% CI=1.45–2.72); p<0.001. However, the adjusted mean CL of NSVTs was similar in patients with (322±34) vs. without MVT (324±26 ms); p=0.3.

Among patients who presented NSVTs and MVTs (n=145 subjects), we analyzed the relationship between the adjusted mean CL of the NSVTs (n=1288 episodes) and the CL of the first appropriate therapy due to MVT occurring subsequently. We found a significant and positive correlation between the two (r=0.88; p<0.001); the strongest correlation was observed in subjects with >5 NSVTs (r=0.97, n=52)). The robustness of such correlation was similar in individuals with ischemic (r=0.86; n=91) versus non-ischemic cardiomyopathy (r=0.90; n=54), and in primary (r=0.86; n=75) versus secondary prevention (r=0.90; n=70). The agreement between the CL of first MVT and the adjusted mean CL of NSVT episodes (GEEM) was determined according to the Bland-Altman Method. The difference between the two values was 2±8.3 ms, with only 7.6% (11/145) of patients in whom the difference between the two CL was outside the concordance limits. The agreement was greater, again, in individuals with >5 NSVTs. As shown in the Figure, in more than 95% of patients both values were within the interval of agreement (0.32±4 ms).

Conclusions

1-The burden of NSVTs occurring early after an ICD implant, but not their CL, is associated with a higher incidence of appropriate therapies due to MVT at follow-up.

2-The CL of the NSVTs and that of the first and subsequent MVTs is virtually the same in patients with higher NSVT burden. Therefore, it could be the same tachycardia, but with different duration.

Figure 1

Funding Acknowledgement

Type of funding source: None