Carl Meurling

Sequential characterization of atrial tachyarrhythmias based on ECG time-frequency analysis

A new method for characterization of atrial arrhythmias is presented which is based on the time-frequency distribution of an atrial electrocardiographic signal. A set of parameters are derived which describe fundamental frequency, amplitude, shape, and signal-to-noise ratio. The method uses frequency-shifting of an adaptively updated spectral profile, representing the shape of the atrial waveforms, in order to match each new spectrum of the distribution. The method tracks how well the spectral profile fits each spectrum as well as if a valid atrial signal is present. The results are based on the analysis of a learning database with signals from 40 subjects, of which 24 have atrial arrhythmias, and an evaluation database with 211 patients diagnosed with atrial fibrillation. It is shown that the method robustly estimates fibrillation frequency and amplitude and produces spectral profiles with narrower peaks and more discernible harmonics when compared to the conventional power spectrum. The results suggest that a rather strong correlation exist between atrial fibrillation frequency and f wave shape. The developed set of parameters may be used as a basis for automated classification of different atrial rhythms.

Characterization of atrial fibrillation using the surface ECG: time-dependent spectral properties

Time-frequency analysis is considered for characterizing atrial fibrillation in the surface electrocardiogram (ECG). Variations in fundamental frequency of the fibrillatory waves are tracked by using different time-frequency distributions which are appropriate to short- and long-term variations. The cross Wigner-Ville distribution is found to be particularly useful for short-term analysis due to its ability to handle poor signal-to-noise ratios. In patients with chronic atrial fibrillation, substantial short-term variations exist in fibrillation frequency and variations up to 2.5 Hz can be observed within a few seconds. Although time-frequency analysis is performed independently in each lead, short-term variations in fibrillation frequency often exhibit a similar pattern in the leads V/sub 1/, V/sub 2/ and V/sub 3/. Using different techniques for short- and long-term analysis, it is possible to reliably detect subtle long-term changes in fibrillation frequency, e.g., related to an intervention, which otherwise would have been obscured by spontaneous variations in fibrillation frequency.

Age-related changes in P wave morphology in healthy subjects

BackgroundWe have previously documented significant differences in orthogonal P wave morphology between patients with and without paroxysmal atrial fibrillation (PAF). However, there exists little data concerning normal P wave morphology. This study was aimed at exploring orthogonal P wave morphology and its variations in healthy subjects.Methods120 healthy volunteers were included, evenly distributed in decades from 20–80 years of age; 60 men (age 50+/-17) and 60 women (50+/-16). Six-minute long 12-lead ECG registrations were acquired and transformed into orthogonal leads. Using a previously described P wave triggered P wave signal averaging method we were able to compare similarities and differences in P wave morphologies.ResultsOrthogonal P wave morphology in healthy individuals was predominately positive in Leads X and Y. In Lead Z, one third had negative morphology and two-thirds a biphasic one with a transition from negative to positive. The latter P wave morphology type was significantly more common after the age of 50 (P < 0.01). P wave duration (PWD) increased with age being slightly longer in subjects older than 50 (121+/-13 ms vs. 128+/-12 ms, P < 0.005). Minimal intraindividual variation of P wave morphology was observed.ConclusionChanges of signal averaged orthogonal P wave morphology (biphasic signal in Lead Z), earlier reported in PAF patients, are common in healthy subjects and appear predominantly after the age of 50. Subtle age-related prolongation of PWD is unlikely to be sufficient as a sole explanation of this finding that is thought to represent interatrial conduction disturbances. To serve as future reference, P wave morphology parameters of the healthy subjects are provided.

Variable interatrial conduction illustrated in a hypertrophic cardiomyopathy population.

Background: Patients with hypertrophic cardiomyopathy (HCM) have a high incidence of atrial fibrillation. They also have a longer P‐wave duration than healthy controls, indicating conduction alterations. Previous studies have demonstrated orthogonal P‐wave morphology alterations in patients with paroxysmal atrial fibrillation. In the present study, the P‐wave morphology of patients with HCM was compared with that of matched controls in order to explore the nature of the atrial conduction alterations.

Prediction of sinus rhythm maintenance following DC-cardioversion of persistent atrial fibrillation – the role of atrial cycle length

BackgroundAtrial electrical remodeling has been shown to influence the outcome the outcome following cardioversion of atrial fibrillation (AF) in experimental studies.The aim of the present study was to find out whether a non-invasively measured atrial fibrillatory cycle length, alone or in combination with other non-invasive parameters, could predict sinus rhythm maintenance after cardioversion of AF.MethodsDominant atrial cycle length (DACL), a previously validated non-invasive index of atrial refractoriness, was measured from lead V1 and a unipolar oesophageal lead prior to cardioversion in 37 patients with persistent AF undergoing their first cardioversion.Results32 patients were successfully cardioverted to sinus rhythm. The mean DACL in the 22 patients who suffered recurrence of AF within 6 weeks was 152 ± 15 ms (V1) and 147 ± 14 ms (oesophagus) compared to 155 ± 17 ms (V1) and 151 ± 18 ms (oesophagus) in those maintaining sinus rhythm (NS). Left atrial diameter was 48 ± 4 mm and 44 ± 7 mm respectively (NS). The optimal parameter predicting maintenance of sinus rhythm after 6 weeks appeared to be the ratio of the lowest dominant atrial cycle length (oesophageal lead or V1) to left atrial diameter. This ratio was significantly higher in patients remaining in sinus rhythm (3.4 ± 0.6 vs. 3.1 ± 0.4 ms/mm respectively, p = 0.04).ConclusionIn this study neither an index of atrial refractory period nor left atrial diameter alone were predictors of AF recurrence within the 6 weeks of follow-up. The ratio of the two (combining electrophysiological and anatomical measurements) only slightly improve the identification of patients at high risk of recurrence of persistent AF. Consequently, other ways to asses electrical remodeling and / or other variables besides electrical remodeling are involved in determining the outcome following cardioversion.

A new de-airing technique that reduces systemic microemboli during open surgery: a prospective controlled study.

OBJECTIVE We have evaluated a new technique of cardiac de-airing that is aimed at a) minimizing air from entering into the pulmonary veins by opening both pleurae and allowing lungs to collapse and b) flushing out residual air from the lungs by staged cardiac filling and lung ventilation. These air emboli are usually trapped in the pulmonary veins and may lead to ventricular dysfunction, life-threatening arrhythmias, and transient or permanent neurologic deficits. METHODS Twenty patients undergoing elective true left open surgery were prospectively and alternately enrolled in the study to the conventional de-airing technique (pleural cavities unopened, dead space ventilation during cardiopulmonary bypass [control group]) and the new de-airing technique (pleural cavities open, ventilator disconnected during cardiopulmonary bypass, staged perfusion, and ventilation of lungs during de-airing [study group]). Transesophageal echocardiography and transcranial Doppler continually monitored the air emboli during the de-airing period and for 10 minutes after termination of the cardiopulmonary bypass. RESULTS The amount of air embolism as observed on echocardiography and the number of microembolic signals as recorded by transcranial Doppler were significantly less in the study group during the de-airing time (P < .001) and the first 10 minutes after termination of cardiopulmonary bypass (P < .001). Further, the de-airing time was significantly shorter in the study group (10 vs 17 minutes, P < .001). CONCLUSION The de-airing technique evaluated in this study is simple, reproducible, controlled, safe, and effective. Moreover, it is cost-effective because the de-airing time is short and no extra expenses are involved.

Detection of autonomic modulation in permanent atrial fibrillation

A new signal processing method for the detection of cyclic variations in atrial fibrillation frequency is presented. The objective was to investigate whether or not respiration, through the autonomic nervous system, modulates the fibrillation frequency in patients with permanent atrial fibrillation. A group of eight patients with permanent atrial fibrillation, atrioventricular block III and a permanent pacemaker were studied during rest, rhythm-controlled respiration, with each breath lasting for 8s (i.e. a breathing frequency of 0.125 Hz), and rhythm-controlled respiration after full vagal blockade by atropine. Using the new method, a spectral peak could be detected, in two of the patients, at the breathing frequency during rhythm-controlled respiration then disappeared after injection of atropine.

The modified Ross operation using a Dacron prosthetic vascular jacket does prevent pulmonary autograft dilatation at 4.5-year follow-up

OBJECTIVE Following the Ross operation, pulmonary autografts tend to dilate over time. This study researches the fate of the pulmonary autograft - at 4.5 years following the modified Ross operation - with special reference to the impact of the modification on (a) pulmonary autograft dilatation, (b) the neo-aortic root geometry, (c) neo-aortic valve function and (d) the coronary artery reserve. METHODS A total of 26 patients who underwent the Ross operation were included in this study; of these, 13 consecutive patients underwent a modified Ross operation in which the free-standing autograft root was supported externally by a Dacron vascular prosthetic jacket (DVPJ). These patients were compared to a cohort of 13 matched patients who were operated on using the conventional Ross technique; all patients were followed up prospectively by echocardiography studies. The patients who underwent the modified Ross operation were also subjected to bicycle ergometry. RESULTS At the 47-month median follow-up, there was no significant increase in the size of the entire neo-aortic root in the patients who underwent the modified Ross operation; in addition, the geometry of the neo-aortic root was also preserved and the left ventricular function had improved significantly, whilst the aortic valve function and excursion remained satisfactory. All patients, with one exception, in the modified Ross operation group exhibited normal exercise capacity. By contrast, there were significant differences in diameters of the aortic root - between the two surgical techniques in favour of the modified Ross technique - following a median follow-up of 23 months in the patients subjected to the conventional Ross operation. CONCLUSIONS Provision of external support to the entire pulmonary autograft with a DVPJ prevents its dilatation following free-standing pulmonary autograft Ross operation when evaluated at the 4.5-year follow-up. The function and the geometry of the neo-aortic root are not affected negatively by this modification and the patients demonstrated normal exercise capacity.

Permanent atrial fibrillation in patients without structural heart disease is not associated with signs of infection by Chlamydia pneumoniae and Helicobacter pylori.

Objective — The objective of this study was to explore the role of Chlamydia pneumoniae and Heliobacter pylori infections in patients with idiopathic permanent atrial fibrillation. Methods and results — Sera from 72 patients with permanent atrial fibrillation without structural heart disease (mean age 69.6 years, 23 women) were analysed for IgG antibodies against Chlamydia pneumoniaeand Helicobacter pyloriand compared in a 1:1 age- and sex-matched case:control manner with those pooled from a healthy reference population of 72 individuals from the same geographical area. After excluding patients with other possible or definite factors known either to cause atrial fibrillation or to affect the prevalence of seropositivity to these agents, the frequency of seropositivity due to one or both of the infectious agents was compared. Serum C-reactive protein (CRP) level was assessed using immunoturbidimetry technique. Both agents were equally common in men and women. Neither seropositivity to Chlamydia pneumoniae (76% vs. 83%, patients vs. control subjests, ns) nor to Helicobacter pylori(57% contra 55%, patients vs. controls, ns) alone reached significance in the comparisons between patients with atrial fibrillation and control subjects. Serum CRP was higher in patients with AF (5.3 mg/L vs. 2.8 mg/L, P < 0.001). Conclusions — Though presence of permanent AF is associated with elevated CRP levels, this elevation is not the result of earlier infections with Chlamydia pneumoniae or Helicobacter pylori or their combination.

Left atrial appendage outflow velocity index is superior to conventional criteria for prediction of maintenance of sinus rhythm after cardioversion. An echocardiographic study in patients with atrial fibrillation of a few months' duration.

OBJECTIVE To investigate whether left atrial appendage outflow velocity alone or in relation to left atrial diameter is a superior predictor of sinus rhythm maintenance after cardioversion compared with traditional clinical or echocardiography parameters. DESIGN Sixty-two patients with their first episode of atrial fibrillation were examined using echocardiography before DC-cardioversion. At one months follow-up, 42 patients had maintained sinus rhythm (group A), and 20 had relapsed into atrial fibrillation (group B). There were no differences in arrhythmia duration or antiarrhythmic therapy between the groups. RESULTS Left atrial diameter measured by echocardiography was smaller in group A (42 mm, 95% CI 40.9-44.1 mm) compared with group B (46 mm, 95% CI 43.4-48.2, p < 0.05). Patients in group A had a higher left atrial appendage outflow velocity at 0.44 m/s (95% CI 0.39-0.49) compared with 0.34 m/s (95% CI 0.30-0.37) in group B (p < 0.01). The ratio of left atrial appendage flow to left atrial diameter was 0.011 (95% CI 0.009-0.012) in group A compared with 0.008 (95% CI 0.007-0.009) in group B, and 63% (95% CI 33-78) of the patients in group A had velocity ratio >0.009 compared with 20% (95% CI 2-38) in group B, (p < 0.01). Stepwise multiple logistic regression analysis showed that a velocity ratio >0.009 was the only predictor for maintenance of sinus rhythm one month after cardioversion with an odds ratio of 6.4 (95% CI 1.9-23.8), (p = 0.004). CONCLUSION The ratio of left atrial appendage outflow velocity to left atrial diameter is superior to the traditionally used criteria for prediction of maintenance of sinus rhythm following DC-conversion of first-episode atrial fibrillation.Objective - To investigate whether left atrial appendage outflow velocity alone or in relation to left atrial diameter is a superior predictor of sinus rhythm maintenance after cardioversion compared with traditional clinical or echocardiography parameters. Design - Sixty-two patients with their first episode of atrial fibrillation were examined using echocardiography before DC-cardioversion. At one months follow-up, 42 patients had maintained sinus rhythm (group A), and 20 had relapsed into atrial fibrillation (group B). There were no differences in arrhythmia duration or antiarrhythmic therapy between the groups. Results - Left atrial diameter measured by echocardiography was smaller in group A (42 mm, 95% CI 40.9-44.1 mm) compared with group B (46 mm, 95% CI 43.4-48.2, p < 0.05). Patients in group A had a higher left atrial appendage outflow velocity at 0.44 m/s (95% CI 0.39-0.49) compared with 0.34 m/s (95% CI 0.30-0.37) in group B (p < 0.01). The ratio of left atrial appendage flow to left atrial diameter was 0.011 (95% CI 0.009-0.012) in group A compared with 0.008 (95% CI 0.007-0.009) in group B, and 63% (95% CI 33-78) of the patients in group A had velocity ratio >0.009 compared with 20% (95% CI 2-38) in group B, (p < 0.01). Stepwise multiple logistic regression analysis showed that a velocity ratio >0.009 was the only predictor for maintenance of sinus rhythm one month after cardioversion with an odds ratio of 6.4 (95% CI 1.9-23.8), (p = 0.004). Conclusion - The ratio of left atrial appendage outflow velocity to left atrial diameter is superior to the traditionally used criteria for prediction of maintenance of sinus rhythm following DC-conversion of first-episode atrial fibrillation.