The Response of the QT Interval to the Brief Tachycardia Provoked by Standing

Q: What are the key findings of this study?

Brisk standing provoked a greater QTc interval increase during maximal tachycardia in LQTS patients than in controls (89 ± 47 ms vs 50 ± 30 ms, p < 0.001).

Q: What is the clinical evidence from this study?

Study design: Case-Control. Population: Long QT syndrome (LQTS) (n=150). Intervention: Long QT syndrome status during brisk standing test vs. Healthy control subjects and noncarrier relatives. Primary outcome: Change in QTc interval (ms) from supine baseline to maximal sinus tachycardia induced by brisk standing (p=<0.001).

Q: What does this research mean for the field?

Brisk standing provokes an exaggerated increase in QTc interval and abnormal QT prolongation in patients with long QT syndrome compared to healthy controls, aiding in LQTS diagnosis. Novelty: ClaimNovelty.INCREMENTAL. Consensus alignment: ConsensusAlignment.NEUTRAL.

Q: What question did this study set out to answer?

To determine whether the short-lived sinus tachycardia provoked by brisk standing exposes diagnostic QT interval abnormalities in patients with long QT syndrome.

Sami Viskin; Pieter Gerard Postema; Zahurul A. Bhuiyan; Raphaël Rosso; Jonathan M. Kalman; Jitendra K. Vohra; Milton Ernesto Guevara-Valdivia; Manlio Fabio Márquez; Evgeni Kogan; Bernard Belhassen; Michael Glikson; Boris Strasberg; Charles N Antzelevitch; Arthur A.M. Wilde

doi:10.1016/j.jacc.2009.12.015

January 30, 2010Journal of the American College of CardiologyOpen Access

The Response of the QT Interval to the Brief Tachycardia Provoked by Standing

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Key result

Brisk standing provokes ~39-ms greater QTc prolongation during maximal tachycardia in LQTS versus controls.

P<0.001
n=150

Why the study?

The QT interval does not shorten instantaneously during heart rate acceleration. Whether the transient, sudden sinus tachycardia provoked by standing exposes abnormal QT interval prolongation of diagnostic value in patients with long QT syndrome was unknown.

Does evaluating the QT and QTc interval response to brief sinus tachycardia provoked by brisk standing improve the diagnostic differentiation between patients with long QT syndrome and healthy control subjects?

Key Points

To determine whether the short-lived sinus tachycardia provoked by brisk standing exposes diagnostic QT interval abnormalities in patients with long QT syndrome.
Recruited 68 patients with long QT syndrome (LQT1 46%, LQT2 41%, LQT3 4%, not genotyped 9%) and 82 control subjects of similar age.
Recorded continuous electrocardiograms during rest in the supine position and immediately after patients briskly stood and remained standing still.
Evaluated QT and corrected QT (QTc) intervals at baseline, maximal sinus tachycardia, maximal QT interval prolongation, and maximal QT interval stretching.
Standing produced similar heart rate acceleration in controls and patients (28 ± 10 beats/min, p = 0.261), but the QT interval shortened by 21 ± 19 ms in controls and lengthened by 4 ± 34 ms in long QT syndrome (p < 0.001).
During maximal tachycardia, QTc increased by 50 ± 30 ms (13 ± 8% from baseline) in controls compared with 89 ± 47 ms (20 ± 11% from baseline) in long QT syndrome (p < 0.001).
QT interval adaptation was particularly impaired in LQT2 patients, whose uncorrected QT lengthened by 21 ± 28 ms compared to an 8 ± 32 ms shortening in LQT1 patients.

Study Design

Type

Case-Control (n=150)

Blinding

One investigator, blinded to the patients’ grouping, performed the measurements

Structured PICO

Does evaluating the QT and QTc interval response to brief sinus tachycardia provoked by brisk standing improve the diagnostic differentiation between patients with long QT syndrome and healthy control subjects?

P

Population

150 participants comprising 68 patients with high-probability or definite long QT syndrome (46% LQT1, 41% LQT2, 4% LQT3, 9% not genotyped) and 82 healthy controls or noncarrier relatives evaluated during a 10-minute supine rest and 5-minute standing ECG test.

E

Exposure

Brisk standing provocative test (resting supine for 10 minutes, then getting up quickly and remaining standing still for 5 minutes during continuous ECG recording; LQTS patients on beta-blockers were tested 26 to 30 hours after their last dosage).

C

Comparator

82 control subjects (healthy volunteers and noncarrier relatives) undergoing the identical supine-to-standing continuous ECG protocol.

O

Outcome

Response of the uncorrected QT and corrected QT (QTc, Bazett's formula) intervals from baseline to maximal sinus tachycardia, maximal QT interval prolongation, and maximal QT interval stretching during 5 minutes of standing.surrogate

Main Result

Absolute Event Rate: 89% vs 50%

p-value: p=<0.001

Limitations

Potential for biased ECG measurements because QT interval duration and T-wave morphology could reveal patient identity despite investigator blinding
Did not evaluate the effects of beta-blocker therapy on the standing response
A few control outliers demonstrated exaggerated QT interval stretching similar to the LQTS group
Although QT interval measurements were performed by a blinded investigator, QT duration and T-wave morphology could often reveal patient identity, creating potential for measurement bias.
The effects of beta-blocker therapy on the standing test were not evaluated.
A few outliers in the control group demonstrated exaggerated QT interval stretching of a magnitude similar to the LQTS group.

Implication

Evaluating QT and QTc interval maladaptation during the abrupt sinus tachycardia induced by brisk standing provides a simple bedside maneuver that significantly improves the diagnostic sensitivity and specificity for long QT syndrome, particularly LQT2.

Abstract

Objectives: This study was undertaken to determine whether the short-lived sinus tachycardia that occurs during standing will expose changes in the QT interval that are of diagnostic value. Background: The QT interval shortens during heart rate acceleration, but this response is not instantaneous. We tested whether the transient, sudden sinus tachycardia that occurs during standing would expose abnormal QT interval prolongation in patients with long QT syndrome (LQTS). Methods: Patients (68 with LQTS [LQT1 46%, LQT2 41%, LQT3 4%, not genotyped 9%] and 82 control subjects) underwent a baseline electrocardiogram (ECG) while resting in the supine position and were then asked to get up quickly and stand still during continuous ECG recording. The QT interval was studied at baseline and during maximal sinus tachycardia, maximal QT interval prolongation, and maximal QT interval stretching. Results: In response to brisk standing, patients and control subjects responded with similar heart rate acceleration of 28 ± 10 beats/min (p = 0.261). However, the response of the QT interval to this tachycardia differed: on average, the QT interval of controls shortened by 21 ± 19 ms whereas the QT interval of LQTS patients increased by 4 ± 34 ms (p < 0.001). Since the RR interval shortened more than the QT interval, during maximal tachycardia the corrected QT interval increased by 50 ± 30 ms in the control group and by 89 ± 47 ms in the LQTS group (p < 0.001). Receiver-operating characteristic curves showed that the test adds diagnostic value. The response of the QT interval to brisk standing was particularly impaired in patients with LQT2. Conclusions: Evaluation of the response of the QT interval to the brisk tachycardia induced by standing provides important information that aids in the diagnosis of LQTS.

Discussion

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Cite This Study

Viskin et al. (2010) conducted a case-control in Long QT syndrome (LQTS) (n=150). Long QT syndrome status during brisk standing test vs. Healthy control subjects and noncarrier relatives was evaluated on Change in QTc interval (ms) from supine baseline to maximal sinus tachycardia induced by brisk standing (p=<0.001). Brisk standing provoked a greater QTc interval increase during maximal tachycardia in LQTS patients than in controls (89 ± 47 ms vs 50 ± 30 ms, p < 0.001).

synapsesocial.com/papers/6ae265fe8ae57796c567dd75 https://doi.org/10.1016/j.jacc.2009.12.015

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The Response of the QT Interval to the Brief Tachycardia Provoked by Standing

Key Points

Study Design

Structured PICO

Main Result

Limitations

Implication

Abstract

Discussion

Cite This Study

The Response of the QT Interval to the Brief Tachycardia Provoked by Standing

Key Points

Study Design

Structured PICO

Main Result

Limitations

Implication

Abstract

Discussion

Cite This Study

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