Echocardiographic findings in professional hockey players

Abstract

Tissue Doppler imaging was used to evaluate the physiological and morphological response in athletes whose cardiac system must not only adapt to intense cardiovascular demands but also support sudden, transient changes in cardiac output. A total of 45 professional hockey players with a mean age of 24 years underwent a baseline transthoracic echocardiographic protocol after a typical morning workout; 12 healthy age- and gender-matched controls were evaluated as a means of comparison. The athletes in this study possessed larger left ventricular diastolic and systolic dimensions than the control group (5.5 ± 0.4 vs 4.9 ± 0.4 cm and 3.9 ± 0.4 vs 3.3 ± 0.4 cm, P < 0.0001). The increase in athletes' septal and posterior wall thickness was not substantial, nor was there a significant difference in left ventricular ejection fraction. The athletes demonstrated consistently larger left ventricular end-diastolic volume (196 ± 34 vs 136 ± 23 mL, P < 0.001) and end-systolic volume (87 ± 20 vs 57 ± 12 mL, P < 0.0001). They also had lower annular septal and lateral early diastolic and systolic tissue Doppler velocities compared with the control group. Thus, characteristic myocardial changes previously reported in elite athletes were also represented in professional hockey players. The lower left ventricular tissue Doppler velocities was a relatively unique finding and probably a consequence of lower postexertion preload levels compared with controls who were measured at rest.

The myocardial adaptations of the athlete's heart have been well described (1). The vigorous, repetitive training regimens that athletes routinely endure lead to a number of characteristic changes, including enhanced diastolic function, larger left ventricular dimensions and mass, and right ventricular dilatation and systolic dysfunction (2). Despite a number of studies that have focused on the various physiological and morphological adaptations of the athlete's heart, the evaluation of these patients using more progressive imaging modalities has remained limited. The recent introduction of tissue Doppler imaging has allowed for measurement of absolute tissue velocities associated with myocardial motion. This technique has led to more accurate evaluation of regional myocardial changes secondary to intense, repetitive strain and produces more reliable assessment of ventricular function (3).

The objective of this study was to evaluate the physiological and structural changes in athletes whose cardiac system must not only adapt to aerobic exercise and intense strength and weight training, but also maintain the reserve necessary to accommodate sudden periods of increased cardiac output. The elite athletes chosen for this study were professional hockey players studied after an intense workout during preseason training camp.

METHODS

The study group consisted of 45 professional hockey players with a mean age of 24 years who underwent a baseline transthoracic echocardiographic protocol after a typical morning workout during training camp. All of the athletes underwent a similar training regimen, which included aerobic and endurance exercises as well as intense strength training. A control group of 12 healthy male nonathletes with a mean age of 27 years underwent the identical protocol at rest. These subjects exercised an average of 3 times per week at no more than 1hour intervals. All subjects provided written informed consent, and the study was approved by the Baylor University Medical Center institutional review board.

The studies were performed on a Philips iE33 portable echocardiographic system. Two-dimensional images were digitally acquired with storage of three cardiac cycles for each view. Measurements included left ventricular (LV) end-diastolic and end-systolic dimensions and volumes, septal and posterior wall thickness, and LV ejection fraction utilizing the biplane Simpson's method. Tissue Doppler images were obtained at 150 frames per second. Color tissue Doppler measurements of LV myocardial function were performed in both the apical four-chamber and two-chamber views. Sample volumes were placed at the septal and lateral mitral annulus for pulsed tissue Doppler measurements of the annular diastolic and systolic velocities. Analysis of myocardial velocities was performed using QLAB quantification software. The two study groups were compared using analysis of variance, with significance established at P < 0.05.

RESULTS

Results (mean ± standard deviation) are displayed in the Table. Compared with the standard population represented by the control group, the athletes had larger body surface areas and lower heart rates. The athletes had evidence of LV remodeling, with larger LV diastolic and systolic dimensions, as well as larger LV volumes, even when indexed for body surface area. However, these larger hearts were not characterized by substantially increased septal or posterior wall thickness. LV ejection fraction was not significantly different between athletes and controls. Although the values were within normal limits, the athletic hearts revealed significantly lower annular septal and lateral wall early diastolic and systolic tissue Doppler velocities compared with the control group.

Table.

Test results in hockey players and matched controls

Variable	Hockey players (n = 45)	Controls (n = 12)	P value
Heart rate (sec-1)	59 ±11	67 ±11	0.02
Systolic blood pressure (mm Hg)	124 ±9	125 ± 12	0.79
Diastolic blood pressure (mm Hg)	71 ±7	71 ±11	0.99
Body surface area (m2)	2.16 ±0.09	1.95 ± 0.11	<0.0001
LV end-diastolic dimension (cm)	5.5 ±0.4	4.9 ±0.4	<0.0001
LV end-systolic dimension (cm)	3.9 ±0.4	3.3 ±0.4	<0.0001
Septal wall thickness (cm)	1.0 ± 0.1	0.8 ±0.1	<0.0001
Posterior wall thickness (cm)	1.0 ±0.2	0.7 ±0.1	<0.0001
LV end-diastolic volume (ml)	196 ±34	136 ±23	<0.0001
LV end-systolic volume (mL)	87 ±20	57 ±12	<0.0001
LV end-diastolic volume index (mL/m2)	91 ±15	70 ±11	<0.0001
LV end-systolic volume index (mL/m2)	40 ±9	29 ±5	0.0002
LV ejection fraction (%)	56 ±4	58 ±4	0.15
Ts-septum (cm/s)	7.6 ±1.0	8.7 ±0.9	0.002
Td-septum (cm/s)	10.9 ±1.5	13.2 ±1.9	<0.0001
Ts-lateral (cm/s)	8.9 ±1.8	11.6 ± 2.7	0.0002
Td-lateral (cm/s)	14.6 ±3.2	19.2 ±2.7	0.0007

LV indicates left ventricular; Ts, tissue Doppler systolic peak velocity; Td, tissue Doppler diastolic peak velocity.

DISCUSSION

The myocardial changes that characterize an athlete's heart are considered to be essentially sport specific. The physiological response to static and dynamic training leads to different adaptations to sustain the specific compulsory demand (4). During aerobic exercise, the consistent exposure of the LV to increased volume during episodes of sustained elevation in cardiac output leads to a propensity for ventricular enlargement (5). Moreover, increased after load during strength and weight training has a propensity to initiate ventricular hypertrophy.

A recent study focusing on the myocardial adaptation of 24 elite speed skaters compared with 15 sedentary subjects revealed larger left atrial and ventricular volumes, enhanced ventricular diastolic function, and attenuated right ventricular systolic function in the athletes' hearts. The enlarged volumes may have resulted from persistent exposure of the LV to changes in preload. The enhanced diastolic function is consistent with the need for rapid recruitment during periods of increased myocardial demand (6). Another study of 24 professional football players revealed significantly increased LV mass, wall thickness, LV end-diastolic and end-systolic volume, and accentuated diastolic function, as evidenced by consistently elevated annular tissue Doppler velocities compared with the control group (7).

Professional hockey players must endure lengthy periods of intense skating while utilizing their physical strength to overpower opponents and perform specialized movements on the ice. In addition, the players must also have the reserve to execute sudden, transient maneuvers that require brief periods of increased cardiac output. The athletes in our study participated in a balanced exercise regimen that included both endurance and strength training. They exhibited increased LV dimensions compared with the control group, which was an expected finding for their level of aerobic and endurance conditioning.

Unanticipated findings in this study included the lack of significant change in septal or posterior wall thickness despite the level of exposure to intense strength training. Although the athletes had larger body surface areas than the controls, the difference between the groups was not as substantial as expected. This may indicate that the athletes' strength training regimen does not achieve the degree of intensity or duration to produce the pressure load necessary to result in wall hypertrophy. This finding would be consistent with previous studies suggesting that the LV wall thicknesses in elite athletes are rarely >1.3 cm (8).

Another uncharacteristic finding in this study group was the uniformly lower tissue velocities in the controls compared with the athletes. This result clearly differs from previous studies, which have consistently revealed higher tissue Doppler velocities in elite athletes (6–7, 9). The most likely explanation is that the athletes were studied immediately after a vigorous workout, which lowers preload and tissue Doppler velocities (10, 11). The controls, on the other hand, were studied at rest. We suspect that tissue Doppler velocities would have been higher in the athletes had they been studied in a resting condition. Unfortunately, the logistics of performing the echocardiograms during a very restrictive training camp schedule did not permit time for resting studies.

Although a characteristic of the study design given the highly specialized subject population, this assessment was clearly limited by the small sample population. A useful variable would have been postexertion analysis using strain rate imaging techniques.

CONCLUSIONS

Characteristic myocardial changes that have been previously reported in elite athletes were also represented in professional hockey players. As a response to the intense, repetitive stress experienced by professional hockey players to maintain optimum physical conditioning, they exhibit characteristic physiological and structural myocardial adaptations. Compared with a standard population, these athletes exhibit larger cardiac dimensions without increased ventricular wall thickness and possess consistently increased LV end-diastolic and end-systolic volumes. The lower left ventricular tissue Doppler velocities demonstrated in these athletes is a novel finding that is likely representative of lower postexertion preload levels in the athletes compared with the sedentary control group.