Ann Thorac Surg 2005;80:2192-2193
© 2005 The Society of Thoracic Surgeons
Original article: Cardiovascular
Invited commentary
Nimesh D. Desai, MD
Division of Cardiac Surgery, Sunnybrook and Women's College Health Sciences Centre, 2075 Bayview Ave, Room H410, Toronto, ON, M4N 3M5 Canada
(Email: nimesh.desai{at}utoronto.ca).
Accurate measurement of myocardial function is critical to determining the need for intervention and to follow the progress of therapy for many structural problems of the heart. In cases of isolated aortic insufficiency (AI), timing of surgery on the asymptomatic patient is predicated on the identification of subtle changes in myocardial function before they become irreversible and negatively affect the patient's long-term prognosis. Unfortunately, such changes are often recognized by current imaging modalities only after irreversible damage and fibrosis has occurred. The lack of a more sensitive way to identify subtle changes in myocardial function represents a significant opportunity for improvement of imaging or biochemical characterization, or both, of asymptomatic patients with isolated aortic insufficiency.
Clinical evaluation of myocardial function traditionally involves the measurement of global left ventricular ejection fraction and chamber dimensions using 2-dimensional echocardiography. Such measures rely on operator-dependant factors such as angle of insonation that introduce variability in measurement. They are also insensitive to the small decrements in function that indicate early, reversible changes to the contractile properties of the myocardium.
Pomerantz and colleagues [1] present an eloquent example of clinical assessment of myocardial strain (ie, a highly sensitive measure of myocardial function) using magnetic resonance imaging (MRI) in patients with AI undergoing aortic valve replacement with a variety of prostheses. Strain is, in simple terms, the percent change in the dimension of an object upon application of a given force. Myocardial strain can be measured clinically by either tissue Doppler echocardiography or MRI. Tissue Doppler echocardiographic measurement of myocardial strain is based on measurement of the velocity between two locations along a Doppler ultrasound beam (ie, strain rate or local velocity gradient), whereas MRI measures the relative displacement of two specific points in the myocardium.
In the current study, the authors identify that subtle decrements in myocardial strain occur within the first 2 years after aortic valve replacement in AI patients who had preoperative left ventricular dilatation. In the face of well-functioning prostheses, advancement of ventricular dysfunction, and potentially myocardial fibrosis, is concerning. The clinical significance of these subtle changes is unknown, but warrants further verification and longer follow-up. More importantly, clinical implementation of MRI-based myocardial strain measurement and highly accurate MRI quantification of chamber dimensions and stroke volume provides clinicians with a more sensitive method of preoperatively identifying which asymptomatic AI patients will benefit from earlier intervention on their aortic valve. This may prevent the late ventricular decompensation seen in this study. Acquisition times of nearly 60 minutes and substantial off-line processing remain limitations at this point, but as technology progresses, this method of imaging may become standard surveillance in patients with asymptomatic aortic insufficiency.
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- Pomerantz BJ, Wollmuth JR, Krock MD, et al. Myocardial systolic strain is decreased after aortic valve replacement in patients with aortic insufficiency Ann Thorac Surg 2005;80:2186-2193.[Abstract/Free Full Text]
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