RESUMO
Background: The relationship of Holter recordings of repolarization length to outcome in long QT syndrome (LQTS) is unknown. Methods: Holter recordings and initial 12 lead ECG QTc were related to outcome in 101 individuals with LQTS and 28 gene-negative relatives. Mean QTc (mQTc) and mean RTPc (R-wave to peak T-wave, mRTPc) using Bazett correction were measured, analyzing heart rates 40 to 120 bpm. Previously reported upper limit of normal (ULN) were: women and children (<15 years), mQTc 454, mRTPc 318 ms; men mQTc 446 ms, mRTPc 314 ms. Results: Measurements in LQTS patients were greatly prolonged; children and women mean mQTc 482 ms (range 406−558), mRTPc 351 ms (259−443); males > 15 years mQTc 469 ms (407−531), mRTPc 338 ms (288−388). Ten patients had cardiac arrest (CA), and 24 had arrhythmic syncope before or after the Holter. Holter values were more closely related to genotype status and symptoms than 12 lead QTc, e.g., sensitivity/specificity for genotype positive status, mRTPc > ULN (89%/86%); CA, mRTPc > 30 ms over ULN (48%/100%). Of 34 symptomatic (CA/syncope) patients, only 9 (26%) had 12 lead QTc > 500 ms, whereas 33/34 (94%) had an mRTPc or mQTc above ULN. In 10 with CA, all Holter measurements were > 15 ms above ULN, but only two had 12 lead QTc > 500 m. Conclusions: Holter average repolarization length, particularly mRTPc, reflects definite LQTS status and clinical risk better than the initial 12 lead QTc. Values below ULN indicate both a low risk of having LQTS and a low risk of cardiac events in the small percentage that do.
RESUMO
BACKGROUND: Normative values for heart-rate corrected repolarisation length are not available in children and are scarce in adults. We wished to define repeatability and normative values of Holter recording measurements of repolarisation length in healthy individuals using a commercially available system, and compare measurements with those from 12-lead electrocardiograms (ECGs). METHODS: Twenty-four-hour (24-) Holter recordings were made on 99 Healthy volunteers: 52 children (7 months to 14 years) and 47 adults (≥15 yrs). Mean and peak values of QTc, and RTPc (R-wave to peak T-wave) were assessed. Bazett heart rate correction was employed for each measurement and only heart rates between 40 and 120 bpm were analysed. The end of the T-wave was defined from the zero-crossing point. QTc was also determined from 12-lead ECGs from the same population by manual measurement recording the longest QTc of leads 2 and V5. The tangent technique was used to define the end of the T-wave. RESULTS: Interobserver repeatability: mean QTc ±15 ms (CI 3.5%), peak QTc ±25 ms (CI 4.5%), mean RTPc ±3 ms (CI 1%), peak RTPc ±44 ms (CI 11%). Mean values were very similar for <15 years and all females and were therefore amalgamated: mean (±2 SD); mean QTc 424 ms (394-454), mean RTPc 291ms (263-319). Values were lower in males ≥15 years; (mean QTc 408 ms (370-446), p<0.01; mean RTPc 274 ms (234-314), p<0.01. The highest mean QTc value was 467 ms in an adult female. QTc from 12-lead ECG: females <15 years 409 ms (384-434) males <15 years 408 ms (383-433), females ≥15 years 426 ms (401-451), males ≥15 years 385 ms (362-408). CONCLUSIONS: Holter measurements of mean QTc and RTPc are highly repeatable. Males ≥15 years have shorter mean repolarisation length over 24 hours than males <15 years and all females. Mean QTc Holter values were on average 15-17 ms longer than QTc from 12-lead ECGs except in females >15 years.
