Severe ECG abnormality associated with systolic dysfunction
Severe ECG abnormality associated with systolic dysfunction of our DM1 patients. Some degree of electro-mechanical correlation has been demonstrated in several previous studies on DM1 subjects. DM1 patients with prolonged PR or QRS intervals are at four-times higher risk to develop LV systolic dysfunction or HF. It is possible that conduction defects cause mechanical impairments, thus treatment of conduction defects with pacemakers and implantable cardioverter defibrillator (ICD) might prevent development of heart failure. On the other hand, it is possible that both electrical and mechanical impairments have the same substrate, fibrosis of the myocardium and conduction system, that was described in several histopathological studies in DM1 patients and DM1 animal models.
Our patients with decreased regional and global contractility of the LV were older. Similarly, systolic dysfunction correlated with age of patients in several studies, and one large study reported that HF was virtually absent in DM1 patients before the age of 40. On the other hand, systolic dysfunction did not correlate with CTG repeat size, neither in our nor in previous studies. In some studies the CTG expansion size correlated with the rate of progression of cardiac disease, however, the correlation with clinical cardiac disease has not been observed in all studies. Cardiac conduction disturbances showed more consistent correlation with male gender, age and duration of disease than with CTG repeats. One possible explanation is that analysis of CTG repeats from peripheral blood leucocytes can underestimate CTG repeat lengths compared to skeletal and order isradipine tissue, where expansion lengths are much longer.
Pure diastolic dysfunction (impaired relaxation) of the LV was present in 9% of DM1 patients, which was even less frequent than in HCs. This partially might be in association with significantly lower percentage of hypertension in DM1 patients. Also, aortic regurgitation that was more common in HCs might cause eccentric LV hypertrophy and structural changes of the myocardium, which can explain diastolic dysfunction. Only one of our DM1 patients with diastolic dysfunction had left atrium enlargement and symptoms of HF. Mild diastolic dysfunction previously was found in 5%–50% of DM1 patients depending on the selection of patients, applied techniques and sample size. Diastolic dysfunction in DM1 might be explained by fibrotic degenerative changes of the myocardium that prevent expansion of the LV, by heart myotonia, and by impaired calcium metabolism in cardiomyocytes. Significance of the diastolic dysfunction in DM1 is not known, and there are no recommendations for treatment of this condition. However, studies on subjects from general population showed that the prognosis in diastolic dysfunction is as poor as in systolic dysfunction. In contrast with systolic dysfunction, diastolic dysfunction in our DM1 patients was not associated with neither ECG abnormalities or with patients age.
The main limitation of our study is that we did not use any non-conventional method for heart investigation. For instance, heart rate variability, heart rate turbulence and electrophysiological studies may identify subtle subclinical cardiac impairments in DM1. Tissue Doppler echocardiography and magnetic resonance imaging (MRI) may reveal systolic and diastolic dysfunction of LV, even in DM1 patients with normal ECG and routine echocardiography. Integrated backscatter ultrasound imaging and contrast MRI may discover heart fibrosis. However, the significance of all of these findings and their relevance for DM1 prognosis is not known since follow-up studies are missing. Furthermore, these methods are not widely available in clinical practice, while our aim was to analyze structural heart abnormalities obtained with routine, widely available methods in clinical settings even in developing countries.