We enrolled 63 patients, aged 68 ± 13 years, with an LV ejection fraction of 61 ± 13%. The clinical characteristics of the entire study population are presented in Table I. The indication for pacemaker implantation in most patients was either sinus node dysfunction (52%) or intermittent second-degree AV block (43%). All patients received a DDD(R) device. During follow-up, 35 patients were not RV paced at all by the device. Twenty-eight patients were RV paced in 1–28% of all beats.
Microvolt TWA Testing During Pacing
All 63 patients completed both pacing protocols. During atrial pacing (AAI mode), microvolt TWA tests were positive, negative, and indeterminate in 13 (21%), 27 (43%), and 23 (36%) patients, respectively (Table II). Indeterminate tests were due to the occurrence of AV block during atrial pacing (n = 17), frequent premature atrial events (n = 3), and due to excessive noise (n = 3). With ventricular pacing (VVI mode), microvolt TWA testing was positive in 12 (19%), negative in 25 (40%), and indeterminate in 26 (41%) patients (Table II). Reasons for indeterminate tests included frequent premature ventricular contractions (n = 15) and excessive noise (n = 11). In none of the patients intermittent 2:1 retrograde conduction was noted during ventricular pacing. When 1:1 retrograde atrial activation was present in the simultaneously recorded ECG and atrial electrograms, this pattern was not associated with positive or increased amplitude TWA. In a subgroup of patients (n = 34), repeated pacing protocols were undertaken to examine the possibility of an order effect on microvolt TWA test results. No differences were found between the initial and repeat bouts of pacing for TWA test results or for any other measured variable.
Concordance Between Pacing Sites
When positive and indeterminate microvolt TWA test results were grouped as nonnegative (Table III), the concordance between atrial and ventricular pacing was 62% (κ= 0.22). When indeterminate test results from both atrial and ventricular pacing were excluded, the concordance rate was 70% (κ= 0.33). Examples of concordant and discordant test results are shown in Figure 1.
Representative microvolt T-wave alternans (TWA) tests. (A) Example of a patient with negative microvolt TWA test results obtained during both atrial (top) and ventricular pacing (bottom). (B) Example of discordant microvolt TWA measurements with a negative test result during atrial pacing and a positive result obtained during ventricular pacing. (C) Example of Wenckebach block occurring at an atrial pacing rate of 100 bpm. The microvolt TWA test during ventricular pacing was negative. From top to bottom: Heart rate (HR) profile, ectopic beats (% bad), noise level, and alternans magnitude (μV). VM = vector magnitude; X, Y, Z = orthogonal chest leads.
Long-term Prognostic Value of Microvolt TWA
Of the 63 study patients, 18 (29%) died during a mean follow-up of 5.9 ± 1.9 years. Kaplan-Meier analysis was used to assess the prognostic relevance of microvolt TWA during atrial and ventricular pacing. Nonnegative test results during atrial pacing were predictive of outcome in our population (P = 0.028) (Fig. 2). There were no differences in baseline clinical characteristics between patients with negative and nonnegative test during atrial pacing (Table IV). Ventricular pacing test results did not predict outcome (P = 0.722) (Fig. 3).
Kaplan-Meier survival curves for 63 pacemaker patients based on negative or nonnegative microvolt T-wave alternans (TWA) testing using an atrial pacing protocol. Mortality was significantly higher in patients with a nonnegative microvolt TWA test result (P = 0.028).
Pacing Clin Electrophysiol. 2011;34(9):1054-1062. © 2011 Blackwell Publishing
Cite this: T-wave Alternans Testing in Pacemaker Patients - Medscape - Sep 01, 2011.