© 2004 by European Society of Cardiology
Copyright © 2004, The European Society of Cardiology
Regional myocardial function in an arrhythmogenic milieu: tissue velocity and strain rate imaging in a patient who had hypertrophic cardiomyopathy with recurrent ventricular tachycardia
aDepartment of Cardiology, G.B. Pant Hospital, New Delhi, India
bDivision of Cardiovascular Diseases and Internal Medicine, Mayo Clinic, 200 First Street SW, Rochester, MN 55905, USA
Received 2 December 2003; received in revised form 10 February 2004; accepted after revision 24 March 2004.
* Corresponding author. khandheria{at}mayo.edu
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Abstract |
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We report the use of tissue velocity and strain rate imaging for detecting marked segmental variations and asynchrony in left ventricular systolic and diastolic functions of a 40-year-old patient with hypertrophic obstructive cardiomyopathy who died of an intractable ventricular tachycardia. These newer techniques have advantages for identifying heterogeneity in regional myocardial function in hypertrophic cardiomyopathy.
Keywords: Hypertrophic obstructive cardiomyopathy; Strain rate imaging; Tissue velocity imaging
Measurement of myocardial velocity with Doppler echocardiography provides a quantitative assessment of regional myocardial systolic and diastolic function.1 However, myocardial velocities detect only regional motion rather than actual regional myofiber deformation and may not be able to differentiate passive motion caused by the tethering effect of adjacent segments. Ultrasonic determinations of strain rate (SR) and strain are newer echocardiographic techniques for studying myocardial deformation.2 Along with tissue velocity imaging, these methods provide a comprehensive temporal and spatial assessment of myofiber activation sequence and regional mechanics.2
Hypertrophic cardiomyopathy (HCM) is characterized by a disorganized myocardial architecture, composed of hypertrophied cardiac muscle, chaotic alignment of myofibers, and areas of scarring resulting from myocyte death and repair.3 The resulting myocardial disarray leads to regional heterogeneity in the functional properties that determine the symptom progression in these patients.3 Myocardial heterogeneity also results in an arrhythmogenic milieu characterized by nonuniform dispersion of cardiac impulse and myofiber activation resulting in life-threatening arrhythmias and sudden cardiac death.3 Although myocardial disarray remains the cornerstone of the disease process in HCM, it is not known whether the risk of future cardiac events can be stratified noninvasively on the basis of the extent of myocardial inhomogeneity. Tissue velocity imaging and SR imaging have been used to quantify the extent of regional systolic and diastolic dysfunction in HCM.4,5 Their potential role in assessment of disease severity as a means to identify patients at risk for future adverse cardiac events remains to be determined.
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Case report |
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A 40-year-old man with HCM was referred to our institution for percutaneous alcohol septal ablation. During investigation in the hospital, he started having recurrent episodes of ventricular tachycardia. Two aborted spontaneously, and electrical cardioversion was required on 5 occasions. In the last episode, ventricular tachycardia degenerated to ventricular fibrillation. Cardioversion was performed, but the patient died of a severe electromechanical dissociation.
At admission, the patient's resting electrocardiogram had shown a sinus rhythm, a normal QRS axis, left ventricular hypertrophy, and symmetric T-wave inversion in all the anterior leads. The echocardiographic examination (Fig. 1), recorded before the occurrence of ventricular tachycardia, showed a markedly hypertrophied left ventricle. The interventricular septum and posterior wall measured 2.8 and 2.3 cm, respectively. There was a systolic anterior motion of the anterior mitral leaflet with a subaortic gradient of 106 mmHg. The left ventricular ejection fraction was 0.62, and no regional wall motion abnormalities were appreciated on 2-dimensional study. Pulsed Doppler at the mitral valve inflow showed a delayed relaxation pattern (Fig. 1D).
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Real-time 2-dimensional color Doppler myocardial imaging data were recorded from the left ventricle with standard apical views with a 2.5-mHz probe (Vingmed System Five; GE Medical Systems, Horten, Norway). Real-time data were acquired as superimposed over an underlying 2-dimensional gray-scale image at a frame rate more than 150/s at a sector angle of 60°. An appropriate velocity scale was chosen to avoid aliasing. The data were stored in a digital format and used for an off-line analysis with dedicated software (TVI-Echopac, Vingmed System Five) for quantifying the regional velocity, tissue tracking, SR, and integrated strain data.
According to convention, longitudinal motion toward the transducer was ascribed positive value and color-coded red to yellow, and motion in diastole away from the transducer was ascribed negative value and coded blue to green. Multiple regions of interest were placed with a curved M-mode, and the color-coded data were displayed as a function of time for assessing regional myocardial motion. Segmental tissue velocity, SR, and integrated strain were analyzed from each myocardial segment by placing the region of interest in the center of the segment. A 10-mm sample gate was used for obtaining the mean Doppler velocity maps, whereas longitudinal strain and SR were computed from velocity data sets of 2 points (<10 mm apart) within each myocardial segment. The variations in velocity (cm/s), SR (1/s), and integrated strain (%) of 3 (basal, mid, apical) segments from each wall were analyzed simultaneously by off-line analysis of color Doppler myocardial imaging data and displayed as spectral tracings. The velocity data referred to the mean myocardial velocities. The SR corresponded to the local spatial velocity gradient, and the regional strain was obtained from the integration of SR curves. For the longitudinal data, a positive SR value represented myocardial lengthening and a negative value represented shortening.
The patient had disorganized activity of the left ventricular myocardium. The tissue velocity and SR imaging from interventricular septum and lateral wall are shown in Fig. 2.
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The systolic motion in the ejection period was markedly reduced in the septum (Fig. 2A). A delayed longitudinal motion of the segment was seen toward the apex in all segments and was followed by an attenuated early and an exaggerated late diastolic relaxation. SR imaging of the septum (Fig. 2B) showed marked attenuation of systolic deformation in all segments. A wave of delayed shortening was identified in the basal segment which corresponded to delayed apical longitudinal motion seen on tissue velocity imaging. The motion and deformation in the lateral wall showed characteristic abnormalities. Tissue Doppler showed fragmentation of systolic waves with delayed apical longitudinal motion (Fig. 2C). Basal and apical segments showed paradoxical systolic expansion in systole (Fig. 2D) followed by delayed contractions. The mid segment showed 2 waves of shortening, an initial wave in the ejection period and an additional delayed wave. Thus, functional heterogeneity in the myocardium included regional variations in the extent of intersegmental shortening (dyssynergy) and timing of peak shortening (dyssynchrony) resulting from a pattern of regional function that ranged from reduced deformation to paradoxical systolic expansions and the presence of delayed longitudinal shortenings.
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Discussion |
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This case highlights the existence of extreme nonuniformity and asynchrony in a patient who had HCM with a ventricular arrhythmia and the potential use of tissue velocity and SR imaging to identify it. To the best of our knowledge, regional variations and asynchrony of this pattern characterized by paradoxical expansions in systole and delayed longitudinal contractions have not been described previously in HCM. This nonuniformity probably reflects an abnormal pattern of intramyocardial activation and function in HCM, which results from myocardial disarray.
Tissue velocity imaging consistently detects regional abnormalities in both hypertrophied and nonhypertrophied parts of myocardium in patients with HCM.4–6 It also detects abnormalities in subjects who are positive for mutations for familial HCM but lack the presence of myocardial hypertrophy. Oki et al.6 evaluated the left ventricular relaxation abnormalities in 20 patients with HCM by using pulsed and color-coded tissue velocity imaging. They found a considerable reduction in peak early diastolic velocities and diastolic asynchrony in the onset of early diastolic relaxation wave after the second heart sound in the septum and posterior wall. However, a pattern of systolic and diastolic asynchrony and inhomogeneity noted in our patient was not found in any of their patients.
In addition to detecting the presence of abnormal myocardium, it is also important to quantify the extent of disease process in HCM. Tissue SR is superior to tissue velocity imaging for detecting these regional variations in myocardial function. Unlike regional velocities, SR is not influenced by the tethering effects of adjacent segments.2 Weidemann et al.7 reported abnormal deformation factors in the hypertrophied mid-septal segment of a 10-year-old patient with nonobstructive cardiomyopathy. No systolic deformation was present in the abnormally hypertrophied mid-septal segments despite a normal tissue velocity. Yang et al.8 documented the presence of regions with paradoxical longitudinal systolic expansion in the interventricular septum. However, in their study, areas with severe regional dysfunction were seen in the mid septum but not in the lateral wall. Similarly, the presence of delayed longitudinal contractions was not reported. These waves are described in patients with coronary artery disease and dilated cardiomyopathy and are important indicators of regional dysfunction and dyssynchrony.9
Regional heterogeneity in myocardium of patients with HCM has been well characterized and can be identified during angiocardiography and invasive electrophysiologic studies. Betocchi et al.10 assessed the regional heterogeneity with biplane left ventriculography in 22 patients with HCM. Systolic and diastolic asynchrony (temporal variations) were observed in 11 (50%) and 5 (23%) patients, respectively. Systolic and diastolic asynergy were found in 82% and 73% of cases, respectively. Regional variations in myocardial thickness and stiffness are the reasons for regional asynergy in these patients, but the origin of asynchrony is not clear. Regional ischemia may contribute to the occurrence of asynchrony.
The electrophysiologic abnormalities in patients with HCM also have been well characterized. Watson et al.11 described the presence of multiphasic local ventricular electrocardiograms in a subset of 18 patients with HCM who were at high risk for sudden cardiac death. Polymorphic ventricular tachycardia that deteriorated to fibrillation was recorded in 8 (44%) patients. Five of these patients had a double electrocardiogram, defined as 2 discrete equidominant poles in the local electrocardiogram, with 40 ms of intervening relatively isoelectric baseline. This pattern of second local depolarization indicated abnormal activation and conduction, a pattern that favors local reentry and initiation of polymorphic ventricular tachycardia. The reason for these electrophysiologic findings was not clear but was linked to the altered myocardial architecture that results in sufficient temporal and spatial dispersion of the stimulating impulse.11
Risk stratification of patients with HCM has become of particular relevance because of the increasing availability of implantable cardioverters and defibrillators and their proven efficacy for preventing sudden death in patients with HCM.3 However, prognostic determinants for identifying patients at risk who would benefit from these devices have remained imprecise, and until now no single disease feature or test has been capable of stratifying risk in all patients.3 Electrophysiologic abnormalities and inducibility of ventricular arrhythmias are known to be prognostic factors in patients with HCM, but it is not known whether identification of extreme heterogeneity in myofiber activation and function could equally stratify these patients.
This case report supports the use of tissue velocity and SR imaging as a noninvasive tool for quantifying the extent of functional heterogeneity in patients with HCM. However, the role of these new techniques for stratifying the extent of myocardial abnormality and assessment of future risk in HCM needs prospective evaluation.
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References |
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[Abstract/Free Full Text] - Watson R.M., Schwartz J.L., Maron B.J., Tucker E., Rosing D.R., Josephson M.E. Inducible polymorphic ventricular tachycardia and ventricular fibrillation in a subgroup of patients with hypertrophic cardiomyopathy at high risk for sudden death. J Am Coll Cardiol (1987) 10:761–774.[Abstract]
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