Patients

Sixty-six patients undergoing septal myectomy without concomitant surgery (valve repair or replacement or maze procedure) done at Toronto General Hospital (Toronto, ON, Canada) for symptomatic HOCM were retrospectively studied. Patients required full baseline clinical records, echocardiograms obtained <6 months before myectomy and on follow-up 6 to 18 months after myectomy, and echocardiographic studies adequate for strain analysis in both baseline and follow-up studies. The control group consisted of 36 healthy subjects without family histories of hypertrophic cardiomyopathy (HCM) and normal echocardiographic findings with similar gender and age distributions. The study was approved by the Research Ethics Board of Toronto General Hospital, University Health Network.

The diagnosis of HOCM was based on echocardiographic findings of septal hypertrophy (≥15 mm) and septal/posterior wall thickness ratio > 1.3, in the absence of any other cause that could account for the degree of hypertrophy detected. Myectomy was offered to patients with unacceptable symptoms despite maximally tolerated pharmacotherapy with LVOT gradients ≥ 50 mm Hg at rest or after provocation (Valsalva maneuver, inhalation of amyl nitrate, or ventricular premature beat), as measured during Doppler echocardiography or cardiac catheterization. Patients were selected for surgical septal myectomy rather than septal ethanol ablation on the basis of their ages, comorbidities, and preferences.

Myectomy Procedure

Myectomy was performed during cardiopulmonary bypass. Septal myectomy was performed through an oblique aortotomy [1]. The length of the septal myectomy ranged from 35 to 50 mm, the width ranged from 20 to 35 mm (wider toward the apex than in the subaortic region), and the depth of the resection was aimed at leaving 8 to 10 mm of residual thickness at the site of the myectomy. Concomitant surgical procedures were also performed if required.

Echocardiography

Baseline (preprocedural) and follow-up (6–18 months after the procedure) transthoracic echocardiographic images were obtained. Echocardiographic studies were interpreted at the time of acquisition. Good-quality echocardiograms were required for speckle-tracing analysis with minimal two-dimensional (2D) frame rate of 40 frames/sec with good LV endocardial border demarcation. Two-dimensional Doppler parameters were measured according to guidelines of the American Society of Echocardiography.

Fraction of Early Apical Reverse Rotation (FEARR)

We used early apical reverse rotation to assess early LV relaxation and measured the fractional decrease in rotation angle from its peak value to its value at 10% of the cycle length later, using the equation FEARR = [θ _peak − θ _{t (peak)+10%CL} ]/θ _peak , where θ is the rotation angle, and CL is the cycle length. Ten percent into diastole time was selected because of previous studies demonstrating the largest decrease in fractional reverse rotation for moderate compared with mild LV hypertrophy.

Statistical Analysis

Data were analyzed using MedCalc version 11.6.1 (MedCalc Software, Mariakerke, Belgium). Continuous data are presented as mean ± SD. Patients were compared with control subjects using unpaired t tests. Premyectomy and postmyectomy comparisons were done using paired t tests. Logistic regression analysis was used to identify independent predictors of clinical response to myectomy. Statistical significance was defined as a P value <.05. For test performance, intraobserver and interobserver variability, intraclass correlation coefficients with 95% confidence intervals (CIs) were calculated.

Preprocedural and Postprocedural Clinical Characteristics

Patient clinical characteristics are summarized in Table 1 . The mean age at the time of surgery was 54 ± 13 years, and 64% were men. Most patients were treated using a combination of β-blockers and/or disopyramide and had New York Heart Association class III symptoms. Major symptoms included dyspnea (94%), chest pain (65%), and syncope (24%). All patients had basal septal myectomy, with concomitant surgery performed in a further 22% of patients (coronary artery unroofing in 15%, coronary artery bypass grafting in 7%). Postmyectomy complete atrioventricular block necessitating permanent pacing occurred in 5% of patients, and new complete left bundle branch block occurred in 40 patients (68%). After myectomy, most patients improved their functional capacity by at least one class, with only 20 patients remaining in New York Heart Association class II or III.

Conventional Echocardiography

Baseline and follow-up 2D Doppler echocardiographic parameters are shown in Table 2 . At baseline, patients demonstrated asymmetric septal hypertrophy, varying levels of LVOT obstruction, moderate mitral regurgitation, and normal LV systolic function. Left atrial volume index was significantly increased. Postmyectomy echocardiography showed a dramatic decrease in the LVOT gradient to nonobstructive levels. LV ejection fraction mildly but significantly decreased, remaining within the normal range. Associated changes included a decrease in the grade of mitral regurgitation and a reduction in the left atrial volume index. Diastolic mitral inflow parameters were similar to premyectomy values. Tissue Doppler velocities demonstrated an increase (+25%, P < .05) in the lateral E′ velocity and a similar decrease in the E/E′ ratio.

Preprocedural Myocardial Mechanics

Preprocedural strain patterns were similar to previous results, namely, lower than normal longitudinal strain, increased circumferential strain, and higher than normal peak apical rotation angle and apical-to-basal twist ( Table 2 ). FEARR was low (28 ± 15%), suggesting abnormal relaxation. Septal wall strain measurements demonstrated a high (19 ± 3%) apical-to-basal longitudinal strain gradient, primarily due to very low basal strain (−10 ± 6). There was also a circumferential apical-to-basal strain gradient of 11 ± 3%.

Postprocedural Myocardial Mechanics

Longitudinal Mechanics

Although there was no significant change in the average longitudinal strain, which remained lower than normal, longitudinal strain decreased at the myectomy segments and increased at the lateral wall ( Table 2 , Figure 1 ). Septal strain demonstrated a significant decrease in its apical-to-basal gradient to 12 ± 2%. This was due to a decrease in apical longitudinal strain from −29 ± 8 to −24 ± 7 ( P < .05), without a change in overall basal strain (−11 ± 5, P = NS).

LV mechanics before and after myectomy. (A) Global longitudinal strain: abnormally low strain, not increased after myectomy. (B) Global circumferential strain: baseline hypernormal strain, decreased after myectomy. (C) Septal longitudinal strain gradient: baseline hypernormal gradient, decreased after myectomy. (D) Apical rotation: baseline hypernormal counterclockwise rotation, decreased to normal values after myectomy.

Circumferential Mechanics

Circumferential strain ( Figure 2 ) decreased to lower than normal levels in the three short-axis levels, resulting in a lower average circumferential strain. Because the decrease was uniform, the apical-to-basal circumferential strain gradient remained similar to its preprocedural magnitude (13 ± 3% vs 8 ± 2%, P = NS).

Apical mechanics before and after myectomy in an example patient. Premyectomy increased apical circumferential strain and rotation ( left ) decreased after myectomy ( right ). Graphs are auto-scaled by Velocity Vector Imaging software; scaling is not identical for all panels.

Myectomy Site versus Non–Myectomy Site Mechanics

Myectomy site segments demonstrated significant decreases in both longitudinal and circumferential strain. Longitudinal strain decreased from −17 ± 5 to −15 ± 4 ( P < .005) and remained at −17 ± 5 at nonmyectomy sites. Mid/basal lateral strain demonstrated a modest yet significant increase from −17 ± 6 to −19 ± 8 ( P < .05). Circumferential strain decreased in both myectomy and nonmyectomy sites (from 28 ± 10 to −22 ± 9, P < .005, and from 29 ± 9 to −25 ± 9, P < .005, respectively). The magnitude of decrease in strain was larger in myectomy compared with nonmyectomy segments (6 ± 7 vs 3 ± 6, P < .05).

Complete Responders versus Incomplete Responders

Patients improving their functional state to New York Heart Association class I after myectomy were defined as complete responders ( n = 46 [70%]) and were compared with patients who remained symptomatic, defined as incomplete responders ( n = 20 [30%]) ( Table 3 ). At baseline, complete responders were a decade younger, had lower LV mass, and demonstrated echocardiographic parameters reflecting better diastolic function and lower pulmonary arterial pressure estimation. Notably, their early relaxation was similar as assessed using FEARR. Independent predictors of partial response to myectomy by logistic regression analysis were older age before myectomy, higher posterior wall thickness, and low lateral E′.

Table 3

Baseline clinical and 2D Doppler echocardiographic characteristics and myocardial mechanics according to clinical response (postmyectomy NYHA class I vs NYHA class > I)

Variable	Complete responders ( n = 46)	Incomplete responders ( n = 20)	Predictors of response by logistic regression ( P value)
Clinical
Age at myectomy (y)	51 ± 13	62 ± 13 ∗	.02
Postmyectomy NYHA class I/II/III	46/0/0	0/19/1
Echocardiography
LV diastolic diameter (cm)	4.1 ± 0.7	4.1 ± 0.5
LV systolic diameter (cm)	2.4 ± 0.5	2.4 ± 0.5
Interventricular septal thickness (cm)	2.0 ± 0.4	2.1 ± 0.3
Posterior wall thickness (cm)	1.1 ± 0.1	1.2 ± 0.2 ∗	.02
Ejection fraction (%)	69 ± 5	68 ± 6
Left atrial volume index (cm 3 /m 2 )	47 ± 15	51 ± 19
Mitral valve
E velocity (m/sec)	0.8 ± 0.2	0.78 ± 0.3
A velocity (m/sec)	0.72 ± 0.19	0.78 ± 0.3
Deceleration time (msec)	245 ± 61	255 ± 83
Mitral regurgitation grade	2.4 ± 0.8	2.0 ± 0.7 ∗	NS
Gradient
LVOT gradient, rest (mm Hg)	64 ± 40	65 ± 34
LVOT gradient, maximal (mm Hg)	94 ± 28	90 ± 22
RVSP (mm Hg)	36 ± 5	41 ± 6 ∗	NS
Tissue Doppler
E′, lateral (cm/sec)	9 ± 4	7 ± 2 ∗	.01
E/E′ ratio, lateral	10 ± 5	13 ± 4 ∗	NS
Mechanics
Average longitudinal strain	−16 ± 4	−15 ± 5
Average circumferential strain	−30 ± 5	−31 ± 5
Rotation (°)
Basal	−7.2 ± 3.5	−9.7 ± 5.4 ∗	NS
Mid	3.0 ± 2.1	3.1 ± 5.5
Apical	9.6 ± 4.9	8.5 ± 4.2
Maximal twist	15.1 ± 6.8	16.8 ± 7.1
FEARR (%)	28 ± 16	29 ± 16

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