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Biomedical subjects

M Malik

Publications and source records attributed to M Malik.

At least 109 records · Page 6Linked to original sources
PubMed1998

Circadian variation in atrial fibrillation in patients with frequent paroxysms.

Determinants of the duration of episodes of atrial fibrillation (AF) in patients with paroxysmal atrial fibrillation (PAF) are poorly understood. However, autonomic tone shows circadian variation and is known to affect atrial electrophysiology. We therefore compared the duration of episodes of AF with an onset during the day (08:00-22:00) to those with an onset during the night in a database of 24-hour ECG recordings in patients with frequent symptomatic PAF. The heart rate in the 30 seconds prior to AF onset was also compared. From 42 recordings, 296 episodes of AF > 30 seconds duration and preceded by > 60 seconds sinus rhythm were identified. The 165 nocturnal episodes tended to be shorter (median = 1.15 min) than the 131 diurnal episodes (median = 1.5 min) and the distribution of nocturnal and diurnal durations was significantly different (P = 0.007; Kolgomorov-Smirnov test). This was also true in recordings containing at least 1 diurnal and at least 1 nocturnal episode. The mean heart rate prior to AF onset was lower at night (62.2 +/- 11.8 vs 75.6 +/- 16.4 beats/min; P < 0.0001 Wilcoxon test). These findings suggest that in patients with frequent symptomatic PAF, autonomic influences affect the duration of episodes of AF and has pathphysiological and therapeutic implications.

Atrial Fibrillation↗
PubMed1998

Evolution of changes in the ventricular rhythm during paroxysmal atrial fibrillation.

Changes in the RR interval within episodes of paroxysmal atrial fibrillation (PAF) have not been fully characterized. A database of 177 24-hour Holter recordings were created from patients with PAF in the CRAFT studies. PAF episodes of > or = 1 minute duration containing < or = 20% noise and preceded by > or = 1 minute of sinus rhythm with < or = 20% noise were selected. Sections of each AF episode containing 10 and 25 RR intervals were identified at the onset, middle, and termination of each episode. Descriptive characteristics (mean, SD, and RMSSD of RR intervals) were calculated within each section, and compared using a nonparametric, paired Wilcoxon test. In 25 patients (17 men, 60.6 +/- 12.2 years old), 231 episodes from 44 recordings met the selection criteria. The mean RR interval increased slightly between the onset and mid-portion of AF episodes (565.9 +/- 128.3 vs 580.3 +/- 144.7 ms, P < 0.001). The RR interval at the termination of AF was significantly greater than that at the start (627.1 +/- 156.1 vs 565.9 ms, P < 10-11) or mid-portion (627.1 +/- 156.1 vs 580.3 +/- 144.7 ms, P < 10-13). SD of the RR interval increased significantly between onset and mid-portion (111.1 +/- 60.2 vs 118.2 +/- 66.7 ms, P < 0.001) and more substantially between mid-portion and termination (118.2 +/- 66.7 vs 201.8 +/- 93.7 ms, P < 10-21). During paroxysms of AF, the mean RR interval and the variability of RR intervals increases. Termination of a paroxysm is preceded by a marked increase in RR interval variability.

Anti-Arrhythmia Agents↗
PubMed1998

Age and gender influences on rate and duration of paroxysmal atrial fibrillation.

UNLABELLED: The influence of age and gender on the character of paroxysmal atrial fibrillation (PAD) has not been described. METHODS: The heart rate (HR) during PAF in patients receiving placebo or antiarrhythmic therapy was analyzed. Data from 177 24-hour Holter recordings were analyzed to mark the onset and termination of PAF and converted into RR interval files. PAF episodes lasting at least 2 minutes and containing < or = 20% noise were included. HR during the first 30-second segment versus during the remainder of the episode, and the duration of PAF episodes were compared among groups of different ages and sex (Wilcoxon test). RESULTS: 236 episodes from 55 recordings in 32 patients (all patients: 61.4 +/- 12.8 years; men (19): 58.5 +/- 12.6 years; women (13) 65.5 +/- 12.4 years, P = ns for difference in age) fulfilled the inclusion criteria. Women had a higher mean heart rate at AF onset (123 +/- 35 beats/min vs 115 +/- 20 beats/min, P = 0.02) and during the remainder of the episode (120 +/- 25 beats/min vs 112 +/- 22 beats/min at the start, P = 0.01, and 116 +/- 26 beats/min vs 108 +/- 18 beats/min subsequently, P = 0.01). Episodes tended to be longer in women (mean 89.8 min vs 50.5 min, P = NS) and in the aged (mean 83.8 min vs 46.9 min, P = NS). CONCLUSION: PAF episodes are associated with faster heart rates and last longer in women, which may reflect differing autonomic responses to AF. A slower ventricular rate during PAF in older patients probably reflects an increasing prevalence of impaired atrioventricular conduction.

Age Factors↗
PubMed1998

Distribution of fast heart rate episodes during paroxysmal atrial fibrillation.

OBJECTIVE: To investigate the defibrillator waiting time (time between the recognition of atrial fibrillation and the actual shock) by studying paroxysmal atrial fibrillation episodes with RR intervals shorter than a certain limit (that is, episodes during which defibrillation should not be attempted). METHODS: Long term 24 hour Holter recordings from a digoxin v placebo crossover study in patients with paroxysmal atrial fibrillation were analysed. In all, 23 recordings with atrial fibrillation episodes of at least 1000 ventricular cycles and with < 20% Holter artefacts or noise were used (11 recorded on placebo and 12 on digoxin). For each recording, the mean ("mean waiting time") and maximum ("maximum waiting time") duration of continuous sections of atrial fibrillation episodes with all RR intervals shorter than a certain threshold were evaluated, ranging the threshold from 400 to 1000 ms in 10 ms steps. For each threshold, the mean and maximum waiting times were compared between recordings on placebo and on digoxin. RESULTS: Both the mean and maximum waiting times increased exponentially with increasing threshold. Practically acceptable mean waiting times less than one minute were observed with thresholds below 600 ms. There were no significant differences in mean waiting times and maximum waiting times between recordings on placebo and digoxin, and only a trend towards shorter waiting times on digoxin. CONCLUSIONS: Introduction of a minimum RR interval threshold required to deliver atrial defibrillation leads to practically acceptable delays between atrial fibrillation recognition and the actual shock. These delays are not prolonged by digoxin treatment.

Anti-Arrhythmia Agents↗
PubMed1998

Computerised measurements of QT dispersion in healthy subjects.

OBJECTIVE: To assess the stability and reproducibility of computerised QT dispersion (QTd) measurement in healthy subjects, as this is presently being incorporated into commercial electrocardiographic systems. METHODS: 70 healthy volunteers (mean (SD) age 38 (10) years, 35 men, 35 women) with a normal 12 lead electrocardiogram (ECG) were studied. From each subject, 70 ECG recordings were taken using the MAC VU ECG recorder (Marquette). In study A, 50 ECGs were recorded in each subject: 10 supine, 10 sitting, 10 standing, 10 holding breath in maximum inspiration, and 10 holding breath in maximum expiration. After a mean interval of 8 (3) days (range 7 to 23), 10 recordings in supine and 10 in the standing position were repeated in each subject (study B). On measurements made using a research version of the commercial software without manual modification, the reproducibility of QTd was assessed by coefficient of variance (CV) and relative error, and comparisons made with other ECG indices. RESULTS: (1) QTd measurements were stable and not influenced by changes in posture and respiratory cycle; (2) there was no difference in QTd measurements between men and women, or between age groups dichotomised at 35 years; (3) no correlation was found between QTd and heart rate or QT interval; (4) short term reproducibility of all QTd measurements (CV 15.6% to 43.8%) was worse than that of conventional ECG indices (CV 1.4% to 5.3%); (5) long term reproducibility of QTd measurements (relative error 27.4% to 31.0%) was also worse than that of conventional ECG indices (relative error 1.8% to 7.9%) (p < 0.0001); (6) the reproducibility of QTd measurements tended to increase when several serial recordings were averaged. CONCLUSIONS: Computerised measurements of global QTd and global QT-SD from 12 lead ECG by the MAC VU/QT Guard system are not significantly altered by changes in posture and respiration. The reproducibility of all QTd measurements is inferior to that of conventional ECG indices in healthy subjects.

Adolescent↗
PubMed1998

Use of spectral turbulence analysis for the identification of patients at high risk for ventricular fibrillation and sudden death in patients with hypertrophic cardiomyopathy.

Hypertrophic cardiomyopathy carries an increased risk of sudden death. The aim of the present study was to assess the predictive value of the signal-averaged ECG, analysed in the time domain and using a new method, spectral turbulence analysis, for the identification of high-risk patients. Two-hundred and forty-six patients with hypertrophic cardiomyopathy were studied. During a mean follow-up of 68 +/- 17 months, 17 patients died suddenly. Patients with sudden death (SD) and/or a history of ventricular fibrillation (VF; n = 25) were compared to patients without SD/VF (n = 221) and to patients without any recognised risk factors for SD (n = 82). There were no differences in mean values of the time domain or spectral turbulence parameters analysed between patients in the SD/VF group and the patients without SD/VF or in the low-risk group. It is concluded that the clinical usefulness of the signal-averaged ECG, analysed in the time domain or as spectral turbulence analysis, is limited in identifying high-risk patients with hypertrophic cardiomyopathy.

Adult↗
PubMed1998

Utility of short-term heart rate variability for prediction of sudden cardiac death after acute myocardial infarction.

Heart rate variability (HRV) computed from 24-hour ECG recording has been associated with an increased risk of malignant arrhythmias after MI. To make HRV analysis more practical, we evaluated prospectively prognostic role of short-term HRV in comparison with other risk stratifiers. Study population consisted of 48 patients with acute MI (mean age 59.6 +/- 10.6 years, 38 males), who were off betablockers. All patients underwent 30-minute ECG recording at supine rest on day 2 and 5 after admission, between 9 and 11 a.m. One ECG channel from a commercial bedside monitor was A/D converted, and subsequently analysed using a purpose-built interactive software. Short-term HRV was computed as the standard deviation of all normal-to-normal RR intervals (SDNN) as well as the square root of the mean of the sum of the squares of differences between adjacent normal RR intervals (rMSSD). Left ventricular ejection fraction (LVEF, in %) was determined using 2D-echocardiography. During one-year follow up, 5 patients (10.4%) died of sudden cardiac death (SCD) and one of non-cardiac death. Subjects who died of SCD presented with significantly lower SDNN parameter on day 5 (28.8 +/- 4.3 vs 39 +/- 18.4, p < 0.006) and similar trend was revealed for rMSSD (12.22.8 vs 24.321, N.S.). Similarly, LVEF was significantly decreased in these patients (35.4 +/- 5.5 vs 49.7 +/- 11.3, p < 0.007). Positive predictive accuracy for prediction of SCD was 17% for rMSSD, 20% for SDNN, 29% for LVEF, and 40% for combination of depressed SDNN (< or = 33 ms) and LVEF (< or = 40). In conclusion, depressed HRV computed from short-term predischarge ECG recordings obtained under standardised conditions is associated with an increased risk of SCD. Such predictive power is substantially increased in combination with depressed LVEF, and this approach seems to be effective as a simple screening method to identify high risk subjects.

Arrhythmias, Cardiac↗
PubMed1997

The effects of reflex parasympathetic stimulation on the QT interval and QT dispersion.

The effect of phenylephrine-induced reflex parasympathetic stimulation on QT interval and its dispersion was studied in 16 healthy subjects with a history of paroxysmal supraventricular tachycardia, both during sinus rhythm and during atrial pacing. Results demonstrate that rapid reflex parasympathetic stimulation does not influence QT interval duration or QT dispersion, and also emphasize the inappropriateness of Bazett's formula, the need for comparison of QT intervals during identical heart rates, and the importance of analyzing all 12 leads of a standard electrocardiogram when assessing the effects of various interventions on the QT interval.

Adult↗
PubMed1997

Usefulness of signal-averaged electrocardiography in evaluation of idiopathic-dilated cardiomyopathy in families.

Family studies have confirmed that familial dilated cardiomyopathy is common and that a large proportion of relatives have mild left ventricular enlargement and therefore potentially early disease. Previous studies have shown that patients with idiopathic dilated cardiomyopathy have abnormalities of the signal-averaged electrocardiogram (ECG). We assessed the usefulness of analysis of the signal-averaged ECG in the evaluation of familial dilated cardiomyopathy. Signal-averaged electrocardiographic recordings were obtained from 58 patients with idiopathic dilated cardiomyopathy, from 161 of their relatives (35 of whom had left ventricular enlargement), and from 59 healthy subjects. Signal-averaged ECGs were analyzed using both time domain and spectral turbulence analysis techniques. The time domain and spectral turbulence analysis variables were markedly abnormal in patients with idiopathic dilated cardiomyopathy compared with relatives considered normal and healthy controls (p <0.05). Late potentials were more common in patients with idiopathic dilated cardiomyopathy (17%) and in relatives with left ventricular enlargement (20%) than in normal relatives (5%) or healthy controls (5%) (p = 0.003). Spectral turbulence analysis was abnormal in 24% of patients with idiopathic dilated cardiomyopathy, 14% of relatives with left ventricular enlargement, 6% of normal relatives, and 5% of healthy controls (p = 0.0006). The sensitivity, specificity, and positive predictive accuracy for identification of relatives with left ventricular enlargement were 20%, 95%, and 54% for time domain analysis and 14%, 94%, and 42% for spectral turbulence analysis. Similar positive predictive accuracy was achievable with spectral turbulence analysis and with time domain analysis. In conclusion, the signal-averaged ECG is frequently abnormal in patients with idiopathic dilated cardiomyopathy and relatives with left ventricular enlargement.

Adult↗
PubMed1997

Mystery of QTc interval dispersion.

Reporting QTc dispersion values without paying attention to the original QT dispersion values and to the heart rate may be seriously misleading because differences in QTc dispersion between clinically well-defined populations may only be caused by differences in the underlying heart rate. This is demonstrated by showing the significant differences in "heart-rate corrected" length of the surname between long-term survivals and nonsurvival patients of acute myocardial infarction.

Diagnostic Errors↗
PubMed1997

Rectal prolapse associated with bulimia nervosa: report of seven cases.

PURPOSE: Rectal prolapse is a condition in which, when complete, the full thickness of the rectal wall protrudes through the anus. Bulimia nervosa is an eating disorder characterized by periodic food binges, which are followed by purging. Purging usually takes the form of self-induced vomiting, laxative abuse, and/or diuretic abuse. We report seven cases of rectal prolapse associated with bulimia nervosa. METHODS: The case histories of seven women with rectal prolapse and bulimia nervosa, average age 29 (range 21-42) years, seen over a period of 11 years (1987-1997) were reviewed. An analysis of the clinical data, including history, presenting physical examination, surgical treatment, and outcome was performed. RESULTS: All seven patients had a diagnosis of bulimia nervosa, made either before or with a diagnosis of rectal prolapse. Rectal prolapse was confirmed in each patient at anorectal examination. Five patients underwent sigmoid resection with proctopexy, one died before operative therapy, and one awaits further treatment. One of the five surgical patients had a recurrence that was managed by a perineal rectosigmoidectomy. CONCLUSION: To our knowledge, despite extensive review of both bulimia nervosa and rectal prolapse as seen in the medical literature, an association between the two has not been described previously. Several aspects of bulimia nervosa, including constipation, laxative use, overzealous exercise, and increased intra-abdominal pressure from forced vomiting are likely causes for the probable relationship with rectal prolapse. The possibility that an atypically young female presenting with rectal prolapse may also have bulimia nervosa should be taken into account by clinicians. This may assist the diagnosis of bulimia nervosa, a disease with multiple morbidities. Conversely, a patient being treated for bulimia nervosa who develops anorectal symptoms may come to earlier diagnosis and treatment for rectal prolapse.

Adolescent↗
PubMed1997

Effects of upright posture on filtered QRS parameter of the signal-averaged electrocardiogram in healthy volunteers.

The effects of upright posture on signal-averaged electrocardiography were studied together with short-term spectral analysis of heart rate variability (HRV) in 20 healthy volunteers (mean age 34 +/- 10 years). Filtered QRS duration from 5-minute epochs and corresponding spectral measures of HRV were computed from digital ambulatory electrocardiographic recordings both at supine rest and during upright tilt (60 degrees). Upright tilt was associated with a significant shortening of filtered QRS (88.2 +/- 8 vs 82.6 +/- 8 msec, p < 0.0001) and with an increase in its maximum amplitude (78.8 +/- 39 vs 87 +/- 48 microV, p < 0.004), whereas the average noise level remained unchanged. In the same time the ratio between low- and high-frequency components of HRV shifted in favor of sympathetic predominance (1.4 +/- 1.2 vs 3.4 +/- 2.9, p < 0.003). No correlation was found between changes in signal-averaged electrocardiography and HRV parameters associated with upright tilt. These data suggest that upright tilt-induced shortening in filtered QRS duration is rather vector-related and does not reflect changes in cardiac autonomic tone. This result must be considered when dynamic analysis of signal-averaged electrocardiography is attempted.

Adult↗
PubMed1997

Phytoremediation of soil metals.

The phytoremediation of metal-contaminated soils offers a low-cost method for soil remediation and some extracted metals may be recycled for value. Both the phytoextraction of metals and the phytovolatilization of Se or Hg by plants offer great promise for commercial development. Natural metal hyperaccumulator phenotype is much more important than high-yield ability when using plants to remove metals from contaminated soils. The hypertolerance of metals is the key plant characteristic required for hyperaccumulation; vacuolar compartmentalization appears to be the source of hypertolerance of natural hyperaccumulator plants. Alternatively, soil Pb and Cr6+ may be inactivated in the soil by plants and soil amendments (phytostabilization). Little molecular understanding of plant activities critical to phytoremediation has been achieved, but recent progress in characterizing Fe, Cd and Zn uptake by Arabidopsis and yeast mutants indicates strategies for developing transgenic improved phytoremediation cultivars for commercial use.

Biological Transport, Active↗
PubMed1997

Sympathetic predominance of cardiac autonomic regulation in patients with left free wall accessory pathway and orthodromic atrioventricular reentrant tachycardia.

AIMS: The aim of this study was to compare cardiac autonomic regulation in patients with a history of paroxysmal supraventricular tachyarrhythmias, such as atrioventricular nodal reentrant tachycardia and atrioventricular reentrant tachycardia, and healthy controls. METHODS AND RESULTS: Seventeen patients with paroxysmal atrioventricular nodal reentrant tachycardia (atrioventricular nodal reentrant tachycardia group), 14 patients with overt preexcitation and paroxysmal atrioventricular reentrant tachycardia caused by a left free wall accessory pathway (atrioventricular reentrant tachycardia group) and 14 healthy control subjects, were studied. The patients and the controls were age and gender matched. Cardiac autonomic regulation was assessed by means of frequency domain analysis of heart rate variability at rest, during head-up tilt, active standing, treadmill exercise and after exercise. The high frequency component (0.15-0.5 Hz) of heart rate variability tended to be lower and the low frequency component (0.04-0.15 Hz) tended to be higher among the atrioventricular reentrant tachycardia patients than in atrioventricular nodal reentrant tachycardia patients and controls. The difference reached statistical significance at rest (P < 0.05) and during standing (P < 0.05 atrioventricular reentrant tachycardia vs atrioventricular nodal reentrant tachycardia and P < 0.01 atrioventricular reentrant tachycardia vs controls). Accordingly, the low-to-high frequency ratio--the marker of cardiac sympathetic regulation--was higher in atrioventricular reentrant tachycardia patients than in atrioventricular nodal reentrant tachycardia patients (P < 0.05 at rest and during standing) and controls (P < 0.01 during standing). CONCLUSION: The cardiac autonomic status in atrioventricular reentrant tachycardia patients was suggestive of a higher sympathetic tone than in atrioventricular nodal reentrant tachycardia patients or healthy controls. This may be related to inhomogeneous ventricular activation in the presence of antegrade conduction via the accessory atrioventricular pathway.

Adult↗