Left ventricular function abnormalities Dilated cardiomyopathy

Most patients with syndrome X have normal left ventricular function and a good prognosis (Arbogast and Bourassa, 1973; Kemp et al, 1973(a)).

Picano and co-workers used dipyridamole infusion rather than exercise and performed two-dimensional echocardiography which revealed the absence of impaired left ventricular functional reserve (Picano et al, 1987).

Nadazdin and colleagues studied a group of patients with syndrome X using two- dimensional echocardiography and doppler during dipyridamole infusion (Nadazdin et al, 1991). None of their patients had any evidence of regional wall motion abnormalities, despite dipyridamole-induced ST segment depression. The authors thought that the absence of regional wall motion abnormalities indicated that the myocardial ischaemia present was diffuse, rather than regional.

Recently, Nihoyannopoulos and colleagues also carried out two-dimensional stress echocardiography and atrial pacing, at rest and immediately post-exercise, in a group of syndrome X patients and a normal control group (Nihoyannopoulos et al, 1991). They found that none of the patients exhibited regional wall motion abnormalities, despite the presence of ischaemic electrocardiographic abnormalities and the occurrence of concomitant angina. In their study, images were obtained within a minute after terminating the exercise test, while the ST segment was still depressed.

The above echocardiographic studies, showing that the left ventricular function is normal in syndrome X, are in disagreement with a number of studies suggesting that regional wall motion abnormalities occur (Legrand et al, 1985; Schofield et al, 1986). Such abnormalities are similar to those concomitant wall motion abnormalities exhibited in patients with CAD due to atherosclerosis, who develop chest pain and ischaemic changes on exercise (Sheikh et al, 1990).

A significant percentage of patients (20% to 50%) also have abnormalities of left ventricular function during exercise, when assessed by radionuclide angiography, even when electrocardiographic evidence of myocardial Ischaemia Is lacking (Schofield et al, 1986; Favaro et al, 1987). Some syndrome X patients also develop such abnormalities after intravenous infusion of dipyridamole (Korhola et al, 1977; Meller et al, 1979).

In a recent study of Yoshio and colleagues (Yoshio et al, 1993) left ventricular functional reserve was evaluated using the continuous radionuclide ventricular function monitor. The authors reported that patients with syndrome X have well preserved left ventricular function before ST segment depression occurs, whereas after ST segment depression appears. It becomes progressively Impaired with an Increasing degree of ST segment depression, and that the left ventricular dysfunction persisted well Into the recovery period.

There are also some reports on findings of left and right ventricular biopsies in patients with syndrome X suggesting that there are no histological abnormalities.

Richardson and colleagues In 1974 reported seven syndrome X patients in whom endomyocardial biopsy specimens showed no vascular abnormalities of coronary vessels less than 150 microns In diameter (Richardson et al, 1974).

Opherk and co-workers took myocardial biopsies from the left ventricular wall and showed normal Intramyocardial vessels, arterioles, metarterloles, capillaries and venules (Opherk et al, 1981). No structural myocardial cell abnormalities could be demonstrated with the only exception being mitochondrial swelling, combined with deposits of small myelin figures.

The absence of histologic coronary vessel abnormalities was also later confirmed by other studies (Kubler and Opherk, 1985).

However, there are some reports in a small number of syndrome X cases suggesting that there are some histological abnormalities. Pasternac and Bourassa reported that a myopathic process may play a part in the pathogenesis (Pasternac and Bourassa, 1983).

Similarly, Opherk and co-workers later reported that patients with syndrome X may develop dilated cardiomyopathy (Opherk et al, 1989). They followed up, over a period of four years, a group of 40 patients with typical effort-related anginal pain, normal coronary arteries and a reduced coronary artery dilatory capacity and assessed their left ventricular function during exercise by gated blood pool scintigraphy.

In this study ail subjects had normal left ventricular function at rest, but a subset of patients with left bundle branch block demonstrated deterioration of left ventricular ejection fraction over this period (>5% change in left ventricular ejection fraction, exercise pulmonary pressure, progressive left ventricular dilation), suggesting a possible co-existent cardiomyopathic process. In contrast, the subgroup with apparently ischaemic ECG responses to exercise showed preserved left ventricular function.

Also, Romeo and colleagues reported a deterioration of left ventricular function at follow- up in eight patients with syndrome X and left bundle block branch presentation (Romeo etal, 1993).

The conflicting results of the above studies might be attributed to the fact that they might have included heterogeneous groups of patients.

A decline in left ventricular function with time in some patients with syndrome X was also demonstrated in another follow-up study (Cannon et al, 1991).

The left ventricular function deterioration over the 4 1/2 year period observed in a significant percentage of the patients studied (25%) was regardless of the presence or absence of evidence of myocardial ischaemia on exercise testing.

In contrast to Opherk*s study the worsening in resting left ventricular function was not restricted to patients with left bundle block. Patients with conduction abnormalities were not included in this study.

Left ventricular endocardial biopsies were also carried out in a subset of patients and showed patchy fibrosis interspersed with myocellular hypertrophy, even in normotensive subjects, but in no case evidence of inflammation or amyloid deposition.

Slight endocardial biopsy abnormalities were also reported by Van Hoeven and Factor (Van Hoeven and Factor, 1990).

Mosseri and co-workers suggested that patients with syndrome X may have histologic abnormalities of the small coronary vessels but this conclusion is controversial as a significant number were hypertensive and had left ventricular hypertrophy (Mosseri et al. 1986).