Methods

Israeli Air Force academy candidates undergo universal screening at the Israeli Air Force Aero Medical Center. The diagnosis of cardiac conditions and, particularly, hypertrophic cardiomyopathy is 1 of the main purposes of this screening process, which includes a thorough physical examination and electrocardiography at rest for all subjects. All subjects undergo a preliminary physical examination at the Israeli Defense Forces recruitment center, and only those in whom no other medical condition is identified are referred to the Israeli Air Force Aero Medical Center. All subjects evaluated at the Israeli Air Force Aero Medical Center undergo a physical examination and electrocardiography at rest.

The blood pressure (BP) was measured twice with a mercury sphygmomanometer after 5 minutes of rest in the sitting position, and the average of the measurements was reported. Subjects with ECG-LVH findings are referred for echocardiography. Those with no such findings and who pass a nonmedical screening process undergo routine echocardiography. This screening echocardiography is Israeli Air Force policy intended to diagnose congenital conditions that could lead to future disqualification of designated aviators.

All aviators in the Israeli Air Force undergo annual screening at the Israeli Air Force Aero Medical Center. Those with ECG-LVH findings are referred for echocardiography. In the absence of such findings, only high-performance aviators undergo routine echocardiography 5 to 10 years after beginning their flying career to diagnose cardiac conditions that could potentially be related to exposure to acceleration forces.

The subjects were divided into 4 groups: group 1, young applicants undergoing echocardiography because of ECG-LVH findings; group 2, young applicants undergoing routine echocardiography in the absence of ECG-LVH findings; group 3, older aviators undergoing echocardiography because of ECG-LVH findings; and group 4, older aviators undergoing routine echocardiography in the absence of ECG-LVH findings.

A standard, at rest, 12-lead recording was made during quiet respiration, with subjects in a supine position. The electrocardiogram was recorded at 25 mm/s and 0.1 mV/mm standardization. All ECG characteristics were determined from digital data using an appropriate software package. Aero medical examiners evaluated 2 commonly used ECG criteria for the diagnosis of LVH: the Sokolow-Lyon Amplitude and the Cornell Amplitude. LVH was defined as a Sokolow-Lyon amplitude of [SV1 + RV5 or RV6] ≥35 mm, or a Cornell amplitude of [RAVL + SV3] ≥28 mm. These criteria are considered as “ECG-LVH findings” throughout our report.

All echocardiographic studies were performed at the Israeli Air Force Aero Medical Center with 1 of 3 devices (HP 500 SONOS, ATL 5000HDI, and PHILIPS HD 11 XE). All studies were performed by 1 of 3 experienced sonographers, and interpreted by 1 of 3 cardiologists who specialized in echocardiography. Transthoracic echocardiography included 2-dimensional, M-mode, and Doppler studies according to the standard American Society for Echocardiography guidelines for obtaining images. The left ventricular mass (LVM) was estimated as 1.05 × (left ventricular end-diastolic diameter [in mm] + posterior wall [PW] thickness [in mm] + intraventricular septum thickness [in mm]) ³ − left ventricular end-diastolic diameter ³ )/1,000. To correct for body surface area, the LVM index was calculated as the LVM/body surface area. LVH was defined as intraventricular septum thickness >11 mm, PW thickness >11 mm, or LVM index of ≥132 g/m ² .

The ethics committee of the Medical Corps of the Israel Defense Force approved the study (IDF-685–2007).

The data were analyzed using IBM SPSS software, version 19.0 (SPSS, Chicago, Illinois) and are presented as the mean ± SD for the study population demographics and LVH criteria. The distributions of all variables were examined using the Kolmogorov-Smirnov nonparametric test. Analysis of variance tests were performed to test the differences among the 4 groups, with Bonferroni post hoc tests for multiple comparisons. To demonstrate the correlation between intraventricular septum thickness, PW thickness, and LVM with demographic variables, Pearson correlations were calculated. Multivariate linear regression analyses were used to correlate the intraventricular septum thickness and PW thickness with the demographic variables and ECG findings. The sensitivity and specificity and positive and negative predictive values of ECG-LVH findings for the echocardiographic diagnosis of LVH were calculated. The significance level was set at p = 0.05.

Results

The young subjects group included 4,709 subjects, of whom 666 (14.1%) underwent echocardiography because of ECG-LVH findings and 4,043 underwent echocardiography in the absence of ECG-LVH findings. The older subject group included 1,294 subjects, of whom 196 (15.1%) underwent echocardiography because of ECG-LVH findings and 1,098 underwent echocardiography in the absence of ECG-LVH findings. The average age of the young group was 18 ± 1 years, and the subjects’ weight, height, and body surface area was 70 ± 11 kg, 177 ± 41 cm, and 2.05 ± 5.64 m ² , respectively. Their BP was within normal limits, with an average of 123 ± 12/71 ± 9 mm Hg. In the entire group, body weight, systolic and diastolic BP, and heart rate were greater in the older than in the young group ( Table 1 ). In the younger group, those with ECG-LVH findings were younger, had a lower body weight and systolic BP, and greater heart rate than those without ECG-LVH findings. In the older subject group, body weight, systolic and diastolic BP, and heart rate were all greater in those with ECG-LVH findings ( Table 1 ).

The interventricular septum thickness, PW thickness, and LVM in the 4 groups are listed in Table 1 . All 3 parameters were elevated in those with ECG-LVH findings; however, this elevation was more pronounced in the older subject group ( Table 1 ). In the younger subjects, the ECG-LVH findings were predictive of LVM (p <0.001) but not of intraventricular septum and PW thickness (p = 0.10 and p = 0.11, respectively). In contrast, in older subjects, they were predictive of all 3 parameters. Echocardiographic LVH was present in 1.6% of young subjects (6.1% of those with and 0.8% of those without ECG-LVH findings) and in 11.3% of older subjects (33.5% of those with and 7.3% of those without ECG-LVH findings). The sensitivity and specificity of the ECG-LVH findings for the echocardiographic diagnosis of LVH in young subjects was 55% and 87%, respectively. In older subjects, the corresponding values were 45% and 88%. The positive predictive value of the ECG-LVH findings for the echocardiographic diagnosis of LVH in young and older subjects was 6.0% and 34%, respectively. The negative predictive value of these criteria in young and older subjects was 99% and 93%, respectively. Age was related to intraventricular septum thickness (r = 0.14) and LVM (r = 0.15), and systolic BP was related to PW thickness (r = 0.17) and LVM (r = 0.13), but diastolic BP and heart rate were unrelated to the echocardiographic parameters.

Multivariate analysis revealed that intraventricular septum and PW thickness were related to systolic BP and heart rate in young subjects and to body surface area, age, and systolic BP in older subjects ( Table 2 ). The ECG-LVH findings were related to intraventricular septum thickness in older subjects, but not in young subjects, and these criteria were related to PW thickness in both young and older subjects. LVM was related to age, systolic BP, and heart rate in young subjects and to body surface area, systolic BP, and heart rate in older subjects. The ECG-LVH findings were related to LVM in both young and older subjects ( Table 2 ).

Table 2

Multivariate analysis determining factors possibly associated with septal and posterior wall (PW) thickness and left ventricular mass (LVM)

Variable	Applicants Aged <20 yr			Aviators Aged >30 yr
	B	SE	p Value	B	SE	p Value
Interventricular septum
Age	0.04	0.012	0.726	0.030	0.004	0.000
Body surface area	0.000	0.002	0.876	1.177	0.272	0.000
Systolic blood pressure	0.008	0.001	0.000	0.010	0.004	0.017
Diastolic blood pressure	−0.002	0.002	0.163	0.006	0.006	0.274
Heart rate	−0.002	0.001	0.024	−0.001	0.003	0.825
Electrocardiographic criteria for left ventricular hypertrophy	0.068	0.049	0.171	1.048	0.126	0.000
Posterior wall
Age	0.013	0.014	0.351	0.012	0.004	0.000
Body surface area	0.000	0.002	0.868	0.999	0.223	0.000
Systolic blood pressure	0.013	0.001	0.000	0.009	0.003	0.005
Diastolic blood pressure	0.001	0.002	0.692	0.004	0.005	0.356
Heart rate	−0.005	0.001	0.000	−0.003	0.003	0.314
Electrocardiographic criteria for left ventricular hypertrophy	0.181	0.057	0.002	0.426	0.103	0.000
Left ventricular mass
Age	1.032	0.410	0.012	−0.109	0.123	0.372
Body surface area	−0.037	0.069	0.591	76.195	7.528	0.000
Systolic blood pressure	0.365	0.042	0.000	0.265	0.111	0.017
Diastolic blood pressure	−0.052	0.055	0.351	0.121	0.152	0.426
Heart rate	−0.219	0.029	0.000	−0.416	0.094	0.000
Electrocardiographic criteria for left ventricular hypertrophy	23.007	1.703	0.000	10.074	3.515	0.004

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