Sex differences and frequency content of the Frank lead signal-averaged ECG in a normal population

To quantify the content of the signal-averaged electrocardiogram (ECG) in normal subjects, 100-beat signal-averaged Frank lead ECGs at a sampling rate of 1,000 Hz and with 16-bit resolution were recorded from 88 women and 102 men with a combined average age of 22 years. The QRS portion of each lead was digitally filtered in four bandwidths: 0-10, 10-60, 60-150, and 150-250 Hz. The root-mean-square voltage of each filtered signal was calculated as an absolute value and normalized as a percentage of the sum of the four filters. Women had significantly lower root-mean-square values in all filtered bands in Frank leads X and Z (P < .01). Normalized data, however, showed no sex difference (P > .05). Sex differences may affect quantitative measurement of the frequency content of the signal-averaged ECG.

Frequency content and sex difference of the Frank lead signal-averaged ECG in a population with significant coronary artery disease. Comparison with concurrent 12-lead ECG morphology

The 12-lead electrocardiogram (ECG) and a 100-beat signal-averaged Frank lead ECG (SAECG) at a sampling rate of 1,000 Hz and with 16-bit resolution were recorded from 52 women and 256 men with significant coronary artery disease presenting for coronary artery revascularization. The QRS portion of each Frank lead was digitally filtered in four bandwidths: 0-10, 10-60, 60-150, and 150-250 Hz. The root-mean-square (RMS) voltage of each filtered signal was calculated as an absolute value and normalized as a percentage of the sum of the four filters, creating 27 variables. Three groups were formed using the presenting 12-lead ECG: N-ECG, ST-ECG, and MI-ECG. Despite variation in 12-lead morphology, concordance was dominant in the RMS values of the SAECG in sex comparisons within and between groups. There was significant sex difference of the RMS values in 6 of the 15 absolute RMS variables within the three groups. Women had no significant between-group difference, and men had a significant between-group differences in five absolute values and one normalized RMS value. P was considered significant at < .05.

Postoperative myocardial damage in patients with coronary artery disease undergoing major non cardiac surgery

A prospective study was carried out in a group of 50 patients with coronary artery disease, presenting for major non-cardiac surgery, to investigate the timing and incidence of further perioperative myocardial damage. A standardised anaesthetic was used. A standard 12-lead ECG was taken immediately before surgery and at 24, 48, and 72 hr after the start of anaesthesia. Blood samples were taken immediately preoperatively and at 6, 24, 48, and 72 hr after anaesthesia for total CK and CK-MB assay. Thirty-three patients (66%) showed ECG evidence suggestive of further infarction, and of these, two (4%) died in the immediate perioperative period. The first ECG change occurred in 27/31 (87%) by 24 hr, in 3/31 (10%) by 48 hr, and 1/31 (3%) by 72 hr. Twenty-nine patients (58%) including the two deaths showed CK-MB enzyme changes. The first elevation in CK-MB was nil at 6 hr and 72 hr, with 23/27 (85%) at 24 hr, and 4/27 (15%) at 48 hr. In 22/50 (44%) ECG and enzymes were correlative. Goldman and Cooperman risk indices were calculated for each patient. The Cooperman risk index was superior to the Goldman scale in the correlation of observed with predicted myocardial morbidity. Patients with ECG changes only before surgery were just as liable to further myocardial damage as those patients with ECG changes and a documented history of a previous infarct and/or symptoms. Myocardial damage is maximal in the first 24 hr after surgery, and may not be adequately predicted by current risk indices.

Early postoperative myocardial morbidity in patients with coronary artery disease undergoing major non-cardiac surgery: correlation with perioperative ischaemia

As a part of a study assessing early postoperative myocardial morbidity in 50 patients with active coronary artery disease undergoing major non-cardiac surgery, the ECG was monitored continuously for 24 hr after the onset of anaesthesia, using a frequency modulated (FM) Holter monitor. Concurrent automated blood pressure and pulse were measured non-invasively at three-minute intervals during anaesthesia and subsequently at five-minute intervals. Thirty patients were monitored with two-site ECG recordings, from modified V1 and V5 (Group A). Twenty patients had seventeen-site ECG monitoring, multiplexing a four by four array of precordial electrodes onto one channel of the frequency modulated recorder (Group B). Tapes were analyzed for noise, supraventricular and ventricular dysrythmias, runs of tachy- and bradycardia, and ST segment changes. These data were correlated with serial standard 12-lead ECGs and CK-MB assay in the 72 hr after surgery. Seven tapes from Group A could not be analyzed. Change (greater than 1 mm) on ST monitoring from both Groups A (14/23), B (14/20), correlated with serial 12-lead ECG and/or CK-MB changes. The majority of first ST change 19/28 (70%) occurred after anaesthesia. In 14/28 (50%) ST change occurred during episodes of tachycardia and elevated blood pressure (greater than 20% above baseline). Nine patients (9/23) in Group A had no ST change; however, six had serial 12-lead ECG and/or CK-MB changes. Six patients (6/20) in Group B had no ST changes, and none of these patients had any change of serial 12-lead ECGs or CK-MB assay. No patient complained of chest pain during the Holter monitoring period. Continual monitoring of heart rate and blood pressure and accurate ST monitoring are essential to detect and treat perioperative myocardial ischemia. A multiple-lead precordial system is substantially more sensitive than traditional two-lead ECG holter monitoring in detecting myocardial ischaemia.

Aspiration beyond endotracheal cuffs

Large-volume low-pressure cuffs have been introduced in an endeavour to reduce the incidence of tracheal mucosal damage. These cuffs when inflated to clinical seal develop folds, which together with low clinical seal pressure may not protect against aspiration. This study compares the incidence of aspiration of dye past a variety of large-volume cuffed tubes and red rubber low-volume cuffs inflated to clinical seal in a group of 30 patients. The incidence of dye tracking past the large-volume cuffs studies was 100 per cent whereas no aspiration of dye was seen past the red rubber tubes. Increasing cuff pressure in the large-volume cuffs beyond clinical seal to 50 cm H2O did not obliterate the dye-filled cuff folds, despite wide variation in the thickness of the cuff material.

Endotracheal cuff pressure and tracheal mucosal blood flow: endoscopic study of effects of four large volume cuffs

Large volume, low pressure endotracheal tube cuffs are claimed to have less deleterious effect on tracheal mucosa than high pressure, low volume cuffs. Low pressure cuffs, however, may easily be overinflated to yield pressures that will exceed capillary perfusion pressure. Various large volume cuffed endotracheal tubes were studied, including Portex Profile, Searle Sensiv, Mallinkrodt Hi-Lo, and Lanz. Tracheal mucosal blood flow in 40 patients undergoing surgery was assessed using an endoscopic photographic technique while varying the cuff inflation pressure. It was found that these cuffs when overpressurised impaired mucosal blood flow. This impairment of tracheal mucosal blood flow is an important factor in tracheal morbidity associated with intubation. Hence it is recommended that a cuff inflation pressure of 30 cm H2O (22 mm Hg) should not be exceeded.

Pressures on endotracheal tube cuffs

The general relationships between the pressure inside an endotracheal tube cuff, the pressure exerted by that cuff on the tracheal wall and the airway pressure have been re-examined in a model system. In relatively recent literature, the tracheal wall pressure at a given cuff volume has been calculated as the difference between intracuff pressures at that volume when the cuff is inflated inside the trachea and when it is inflated whilst suspended freely in air. This has been used as a general relationship, as an alternative to direct measurement in real and model tracheas. In this study, the directly measured pressure was not generally equal to the pressure as calculated above.