Biomedical subjects
Publications and source records attributed to Emmanuel N Simantirakis.
The sleep apnoea syndrome is a particularly common health problem associated with increased cardiovascular morbidity and mortality, as well as harmful socioeconomical and familial complications. In this article, the diagnostic and therapeutic role of cardiac pacing in this syndrome is discussed.
BACKGROUND: The role of atrial overdrive pacing (AOP) in sleep apnea remains uncertain. We prospectively evaluated the effect of AOP after 24 hours and after one month in patients with the obstructive sleep apnea-hypopnea syndrome and compared it with the use of nasal continuous positive airway pressure (n-CPAP). METHODS: We studied 16 patients with a moderate or severe case of the obstructive sleep apnea-hypopnea syndrome (baseline mean apnea-hypopnea index, 49) and normal left ventricular systolic function in whom a dual-chamber pacemaker had been implanted. After 48 hours, the patients were randomly assigned to AOP (pacing at 15 bpm above the spontaneous mean nocturnal heart rate) or backup atrial pacing (pacing at a heart rate below 40 bpm); the latter group began n-CPAP therapy one day later. After one month, the two groups switched therapies and were followed for an additional month. Polysomnographic studies were performed at baseline, on the first night after randomization, at crossover, and at the end of the study. RESULTS: During AOP, no significant changes were observed in any of the respiratory variables measured. The change in the apnea-hypopnea index at one month with AOP was +0.2 (95 percent confidence interval, -2.7 to +2.3; P=0.87). In contrast, all variables improved significantly after one month of n-CPAP (change in the apnea-hypopnea index, -46.3; 95 percent confidence interval, -56.2 to -36.5; P<0.001). CONCLUSIONS: Nasal continuous positive airway pressure therapy is highly effective for the treatment of the obstructive sleep apnea-hypopnea syndrome, whereas AOP has no significant effect.
OBJECTIVES: The aim of the study was to evaluate whether left ventricular (LV) mechanics are better under LV-based pacing than under right ventricular (RV) apical pacing in patients with permanent atrial fibrillation (AF) after atrioventricular junction (AVJ) ablation. BACKGROUND: "Ablate and pace" is an acceptable therapy for drug-refractory AF. However, the RV apical stimulation commonly used seems to interfere with the beneficial hemodynamic effect of regularization of heart rhythm. METHODS: The study included 12 patients (5 men, mean age 62 +/- 8.3 years), 6 with impaired and 6 with normal LV systolic function. All of them had a biventricular pacemaker system implanted and underwent atrioventricular node ablation for drug-refractory chronic AF. Using a conductance catheter, we analyzed LV pressure-volume loops during routine coronary angiography in order to evaluate short-term changes in LV mechanics during RV apical and LV-based (LV free wall or biventricular) pacing. RESULTS: Compared with RV pacing, LV-based pacing significantly improved the indexes of LV systolic function (i.e., end-systolic pressure and volume, cardiac index, stroke work, preload recruitable stroke work, maximal rate of rise of LV pressure [dP/dt(max)], LV ejection fraction, and end-systolic elastance). The LV diastolic filling indexes, end-diastolic pressure and volume, were better during LV-based pacing, whereas LV diastolic function indexes, -dP/dt(max), passive diastolic chamber stiffness, and time constant of LV isovolumic relaxation showed no clear change. CONCLUSIONS: In the short term, LV-based pacing is superior to RV apical pacing in terms of contractile function and LV filling after AVJ ablation for drug-refractory AF.
AIM: In this new era of insertable loop recorders, we studied obstructive sleep apnoea-hypopnoea syndrome (OSAHS) patients in order to evaluate their arrhythmias and the beneficial effect of Continuous Positive Airway Pressure treatment (CPAP), over a long-term period. METHODS AND RESULTS: We enrolled 23 patients (16 men, 50 +/- 11 years) with moderate and severe OSAHS. In all patients, an insertable loop recorder capable of monitoring the heart rhythm for 16 months was implanted. Cardiac pauses >3 s and bradycardic episodes <40 bpm during a 2-month period before, and for 14 months after, the CPAP application, were noted. In each period, the patients underwent two 24-h Holter recordings. Before treatment, 11 patients (47%) revealed severe cardiac rhythm disturbances, mostly nocturnal. Holter recordings showed disturbances in only 3 (13%) patients (P=0.039), those in whom the insertable loop device had recorded frequent episodes. Eight weeks after the initiation of treatment, the total number of the recorded episodes tended to decrease while, during the last 6 months of the follow-up, no episodes were recorded. CONCLUSION: Approximately half of OSAHS patients evidence severe cardiac rhythm disturbances, which are significantly reduced by CPAP. Holter recordings seem unable to precisely describe the incidence of severe brady-arrhythmias and the effect of treatment.
Spectral analysis of heart rate variability was used to compare the changes in autonomic function during tilting in young and older patients with vasovagal syncope. Twenty-four young (age 28 +/- 8 years) and 31 older (56 +/- 5 years) patients with unexplained syncope and a positive tilt test and 25 controls (age 48 +/- 12 years) were included in the study. Frequency-domain measurements of the low (LF) (0.06-0.15 Hz) and high (HF) (0.15-0.40 Hz) frequency bands and the ratio of LF to HF were computed from Holter recordings for 4-minute intervals before and immediately after tilting and just before the end in all groups. Syncopal patients showed a different pattern of response to tilting from controls in all spectral indexes. Young and older patients showed the same pattern of changes in all measurements, even though certain differences were observed. The LF after tilting reduced more in the older (-20 +/- 7% vs -14 +/- 5%, P < 0.001), while HF reduced more in young patients (-17 +/- 8% vs -8 +/- 3%, P < 0.001). Young patients showed mainly a cardioinhibitory type (71%) of response whereas a vasodepressor type response predominated (68%) in the older patients. The autonomic nervous system appears to play an important role in the pathophysiological mechanism of vasovagal syncope. This role is similar in young and in older patients and this should be taken into account in the therapeutic approach to the condition. Specific differences between age groups may be related to the type of vasovagal syncope.
Cardiac resynchronization has proved a valuable adjunctive therapy in heart failure patients with ventricular conduction disturbances. It improves the patient's clinical status and quality of life, increases functional capacity and causes left ventricular reverse remodeling. The application of this new therapeutic method is expected to affect the pacemaker implantation rate, although the exact degree cannot yet be calculated. One of the main determining factors is the number of patients who are candidates for resynchronization therapy. Although this cannot be estimated precisely, it seems that it does not exceed 10-14% of heart failure patients. Additional factors that will influence the implantation rate, at least during the next few years, are the familiarization of cardiologists with the new implantation technique and follow-up, the availability of cardiac laboratory time and the cost of this new therapy. Although the latter seems high, the financial burden will be minimal when it is taken into consideration that it will lead to a decrease in the number of hospital admissions and a significant reduction in the number of hospitalization days, the greatest determining factors in the current high management cost of heart failure patients. Further to the above, taking the differences between the implantation rates of conventional pacing systems into account in different European countries, the same could be expected of biventricular systems. Thus, although the incidence of heart failure is constantly increasing and conduction disturbances are frequent in such patients, we believe that the implantation rate of biventricular systems in Europe will not exceed an average of 10 per million population, fluctuating according to the country. In conclusion, resynchronization therapy has been established in special subsets of heart failure patients. Due to the epidemiological characteristics of heart failure, the implantation rate is expected to rise. Possible education and/or training issues that appear will be addressed respectively, enabling all suitable patients to enjoy the benefits this new therapeutic technique ensures.
The aim of this study was to investigate myocardial perfusion and adrenergic innervation in patients with intraventricular conduction disturbances and to detect any changes caused by alteration of the ventricular activation sequence as a result of right ventricular apical pacing. We studied 15 patients with right bundle branch block (RBBB) and left anterior fascicular block (LAFB), while 15 healthy individuals served as controls. All patients underwent planar and single-photon emission computed tomography (SPECT) myocardial imaging after intravenous infusion of 5mCi 123I-metaiodobenzylguanidine (123I-MIBG) and a SPECT thallium201 myocardial perfusion study before and 3 months after pacemaker implantation. The heart to mediastinum ratio was calculated during the 123I-MIBG study in order to assess the global cardiac sympathetic activity and was significantly smaller in patients than in controls (P < 0.001). Patients with RBBB and LAFB revealed regional adrenergic innervation defects, mostly in the inferior and posterior walls. After a medium-term pacing period, a redistribution of 123I-MIBG uptake was detected, with aggravation of adrenergic innervation defects in the apical and posterior walls and amelioration in septal and anterior walls. Five patients showed perfusion defects that remained unchanged after pacing. Two others displayed mild myocardial perfusion defects that did not exist before pacing. In conclusion, patients with RBBB and LAFB reveal global and regional disturbances of myocardial adrenergic innervation, which shows redistribution as a result of the altered propagation of the ventricular electrical activation. To a smaller degree these patients reveal myocardial perfusion disturbances in which pacing has a limited medium-term effect.
STUDY OBJECTIVES: Asynchronous ventricular activation, as induced by ventricular pacing, is known to affect left ventricular (LV) systolic and diastolic function and myocardial blood flow. However, it is not clear whether the long-term disturbances it causes are reversible after the restoration of the normal ventricular activation sequence. DESIGN: In this study, we used the conductance catheter method and a Doppler guidewire to assess the changes in LV mechanics, and correspondingly in myocardial blood flow, after the restoration of the normal ventricular activation sequence in patients with long-term right ventricular apical pacing. PATIENTS: Sixteen patients (mean [+/- SD] age, 61 +/- 11 years; 9 men) with right ventricular apical stimulation and complete ventricular pacing capture for a very long period were studied. In eight patients, we analyzed pressure-volume loops before and immediately after the restoration of the normal ventricular activation sequence, and in the remaining eight patients the myocardial blood flow and flow reserve were analyzed. MEASUREMENTS AND RESULTS: End-systolic elastance (Ees) [5.503 +/- 0.6 vs 4.287 +/- 0.28 mm Hg/mL, respectively; p = 0.003] and its ratio to effective arterial elastance (1.63 +/- 0.51 vs 2.00 +/- 0.64, respectively; p = 0.009), which are indexes of systolic function and ventriculoarterial coupling, respectively, improved significantly after restoration of the normal ventricular activation sequence. Indexes of diastolic function and the predicted myocardial oxygen consumption (MO(2)) showed no clear change. Coronary flow in the dominant coronary artery increased significantly (46.55 +/- 14.12 vs 71.55 +/- 27.53 mL/min, respectively; p = 0.002), while the coronary flow reserve in the same artery decreased (3.5 +/- 1.0 vs 2.6 +/- 0.5, respectively; p = 0.008). CONCLUSIONS: The restoration of a normal activation sequence after long-term ventricular asynchrony enhances acutely contractile function without affecting MO(2). These changes in LV function do not appear to have causal relationships with myocardial blood flow changes.
This study evaluated the possibility of diagnosing chronic myocardial infarction in the presence of the pacing electrocardiogram. Forty-five patients with known myocardial infarction (anterior 23, inferior 22) and 26 healthy controls were studied. After coronary angiography, pacing was applied from the right ventricular apex, and the sensitivity, specificity, and average diagnostic accuracy of five criteria on the paced electrocardiogram were assessed: (1) Notching 0.04 second in duration in the ascending limb of the S wave of leads V3, V4, or V5 (Cabrera's sign); (2) Notching of the upstroke of the R wave in leads I, aVL, or V6 (Chapman's sign); (3) Q waves > 0.03 second in duration in leads I, aVL, or V6; (4) Notching of the first 0.04 second of the QRS complex in leads II, III, and aVF; (5) Q wave > 0.03 second in duration in leads II, III, and aVF. The most sensitive criteria, for anterior and inferior myocardial infarctions were Cabrera's and Chapman's (91.1 and 86.6%, respectively). All criteria had low specificity (range 42.3-69.2%). The combination of Cabrera's and Chapman's sign decreased the sensitivity to 77.7%, but increased specificity to 82.2%. The sensitivity and specificity of all the criteria were independent of the myocardial infarction site. In paced patients, the application of electrocardiographic criteria, and especially the combination of Cabrera and Chapman, provides useful clinical information in recognizing prior myocardial infarction but not in assigning the specific infarct site.
INTRODUCTION: Sleep apnoea, which constitutes a major social problem because of its high prevalence and its emerging association with cardiovascular morbidity and mortality, is known to affect autonomic nervous system activity. We assessed the hypothesis that treatment of sleep apnoea patients with continuous positive airway pressure (CPAP) alters the indices of heart rate variability (HRV) that reflect sympathetic and parasympathetic autonomic nervous system activity. METHODS: We studied 26 patients (18 men, aged 49.2 +/- 7.6 years) with obstructive sleep apnoea-hypopnoea syndrome. In all patients, a 24-hour Holter recording was obtained one week before initiation of CPAP treatment and another one two months later. From these recordings we assessed the time domain indices of HRV (pNN50, rMSSD, SDNN, SDANN, SD) during the day (08:00-23:00) and during the night hours (23:00-08:00) as well as their post-treatment changes. The same HRV indices were also assessed in a group of 19 age and sex matched controls, without sleep apnoea. RESULTS: No significant differences in the HRV indices were observed during the daytime hours, while during the night both pNN50 and rMSSD were significantly higher in patients compared to controls (19.5 +/- 12.5 vs. 13.8 +/- 9.7, p=0.001, for pNN50 and 54.7 +/- 23.1 vs. 44.0 +/- 15.9, p=0.001, for rMSSD, for patients and controls respectively). No such differences were observed in any of the monitored indices following CPAP treatment. CONCLUSIONS: The indices that reflect parasympathetic activity are increased during the night in patients with obstructive sleep apnoea syndrome. CPAP treatment reduces the night time vagal indices of HRV to resemble those of normal controls. The reduction of parasympathetic activity may be one of the mechanisms responsible for the alleviation of bradyarrhythmic episodes following the initiation of CPAP therapy.