Left Ventricular Twist Mechanics in a Canine Model of Reversible Congestive Heart Failure: A Pilot Study

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Background

Left ventricular (LV) twist dynamics play an important role in LV systolic and diastolic function. The aim of this preliminary study was to investigate LV twist dynamics in a canine model of reversible congestive heart failure (CHF).

Methods

Pacing systems were implanted in adult dogs, and continuous chronic right ventricular pacing (230-250 beats/min) was applied until CHF induction. Pacing was then stopped to allow the heart to recover. Echocardiography and LV catheterization were performed at baseline, during CHF while pacing was temporarily switched off, and during recovery. LV twist was computed as the difference between apical and basal rotation measured using 2-dimensional speckle tracking. Torsion was further calculated as LV twist divided by the LV long axis. The untwisting rate was computed as the peak diastolic time derivative of twist.

Results

In 6 dogs that completed the study, we found that CHF developed after 2 to 4 weeks of pacing, with LV end-diastolic volume, end-systolic volume, end-diastolic pressure, and the time constant of relaxation during isovolumic relaxation period (τ) all increasing significantly compared with baseline and recovering to normal levels 2 to 4 weeks after pacing was stopped. LV twist, torsion, and untwisting rate decreased significantly with CHF compared with baseline and improved during recovery from CHF.

Conclusion

LV twist dynamics reflect pacing-induced CHF and its reversal as assessed by echocardiographic speckle tracking.

Section snippets

Animal Preparation

The study protocol was approved by the animal care and use committees of the Institute of Biosciences and Technology, Texas A&M University, and of the Methodist Hospital Research Institute. The study adhered to the Public guidelines for the care and use of laboratory animals. Thirteen adult male mongrel dogs were studied (weight, 35-40 kg). In each procedure, the dog was sedated by the intramuscular injection of xylazine (0.75-1.5 mg/kg) and atropine (0.02-0.06 mg/kg). Anesthesia was induced by

Animals

Complete data sets were available at all 3 stages of the study from 6 dogs and were analyzed and compared using repeated-measures analysis of variance. Data from the other dogs were lost during follow up because of premature death, experimental complications, implanted pacing system failure, or poor image quality.

Changes in Echocardiographic and Hemodynamic Variables

As summarized in Table 1, LV end-diastolic volume and LV end-systolic volume increased, while EF decreased significantly in all dogs during CHF. All of these variables returned to

Discussion

We performed a pilot study to investigate LV dynamics in a canine model of pacing-induced heart failure. We demonstrated that LV twist, torsion, and untwisting rate were impaired during CHF and improved upon recovery from heart failure.

The quantification of LV function is usually cumbersome. The most frequent measure of LV systolic function is EF. The measurement of EF as recommended by the American Society of Echocardiography requires accurate manual tracing of the LV endocardium, which can be

Conclusions

LV twist dynamics, as assessed by echocardiographic speckle tracking, reflect pacing-induced CHF and its reversal. Our preliminary findings suggest that LV twist or torsion may be used to monitor LV function during treatment of heart failure.

Acknowledgment

We thank April Gilbert, BS, and Daryl Schulz, RTR, for their technical assistance.

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This study was supported in part by research grant R01HL068768 from the National Institutes of Health, Bethesda, MD, and a research grant from the Cardiac Rhythm Management Division, St. Jude Medical, Sylmar, CA (both to Dr Khoury).

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