Anterior-posterior Chest Diameter Research Articles

Anatomical considerations for the subcutaneous implantable cardioverter-defibrillator (SICD) implantation: a cadaver-based analysis

Abstract Background Subcutaneous implantable cardioverter-defibrillators (SICDs) offer primary and secondary prevention of sudden death without transvenous leads in individuals not requiring pacing therapy. Intermuscular placement of the SICD generator between the latissimus dorsi (LDM) and serratus anterior (SAM) muscles is often recommended. This specific technique results in reduced defibrillation impedance and subsequently optimal defibrillation thresholds, reduced risk of pocket complications and infections, reduced device migration, and enhanced patient comfort and cosmetic outcomes. Despite the recommendation for an intermuscular implant technique utilizing a mid-axillary incision line, there is limited research describing this anatomical space to avoid complications. In this anatomic study, we examined this anatomical space. Our aim was to provide a better understanding of the interplay between the involved muscles and a proper location of an incision line. We also defined the location of the long thoracic nerve (LTN) relative to this space, which if transected, would lead to a winged scapula. Methods We examined 18 cadavers; 12 (66.7%) were female donors and 6 (33.3%) were males. We measured the distance from the anterior border of the LDM in relation to the cadaver back (A) and in relation to the anterior-posterior diameter of the chest (B). We performed these measurements at the 5th and 7th rib levels, and then averaged these measurements. We also measured the distance from the back to where the LTN enters SAM at the 4th, 5th, and 6th ribs. Results Analysis of the obtained data showed that the mean distance from the back to the anterior border of LDM at the 5th rib was 7.55 cm (5.65 – 10.85 cm) and at the 7th rib was 7.60 cm (5.35– 10.35 cm). Mean distance from the back to the anterior LDM border in both 5th and 7th ribs combined was 7.58 cm (5.50 – 1.06 cm). The mean anterior-posterior diameter of the chest wall at the fifth rib was 21.45 cm (18.55 – 24.75 cm). The mean A/B ratio (that is the ratio between the distance from the back to the anterior LDM border in comparison to the anterior-posterior chest diameter) was 0.4 with a standard deviation of +/- 0.1 (range 0.27-0.45). The LTN was running anterior to the LDM border at the 4th rib level, and posterior to the LDM border at the 5th and 6th ribs level. The LTN entered the SAM at the 4th rib level in 6.6%, at the 5th rib in 46.6% and at the 6th rib in 46.6% of cadavers. Discussion Intermuscular technique for S-ICD implantation is recommended as the preferred procedural approach. In our postmortem study, the anterior LDM border was variable but posterior to the mid-axillary line with a variable A/B ratio of 0.27 – 0.45. Our study also demonstrates the proximity of the long thoracic nerve (LTN) in comparison to the anterior LDM border. Caution should be taken when implanting S-ICD devices to avoid LTN injury.

Chest Compression Depth Targets in Critically Ill Infants and Children Measured With a Laser Distance Meter: Single-Center Retrospective Study From Japan, 2019-2022.

Current resuscitation guidelines recommend target chest compression depth (CCd) of approximately 4cm for infants and 5cm for children. Previous reports based on chest CT suggest these recommended CCd targets might be too deep for younger children. Our aim was to examine measurements of anterior-posterior chest diameter (APd) with a laser distance meter and calculate CCd targets in critically ill infants and children. A retrospective descriptive study. Single-center PICU, using data from May 2019 to May 2022. All critically ill children admitted to PICU and under 8 years old were eligible to be included in the retrospective cohort. None. The chest APd measurements using a laser distance meter are part of our usual practice on the PICU. Target CCd and the over-compression threshold CCd for each age group was calculated as 1/3 and 1/2 of APd, respectively. In 555 patients, the median (interquartile range) of the calculated target CCd for each age group was: 2.7 cm (2.5-2.9 cm), 2.9 cm (2.7-3.2 cm), 3.2 cm (3-3.5 cm), 3.4 cm (3.2-3.6 cm), 3.4 cm (3.2-3.6 cm), 3.6 cm (3.4-3.8 cm), 3.6 cm (3.4-4 cm), and 4 cm (3.5-4.2 cm), for 0, 2, 3-5, 6-8, 9-11, 12-17, 18-23, 24 to less than 60, and 60 to less than 96 months, respectively. Using guideline-recommended absolute CCd targets, 4 cm for infants and 5 cm for children, 49% of infants between 0 and 2 months, and 45.5% of children between 12 and 17 months would be over-compressed during cardiopulmonary resuscitation. In our cohort, the 1/3 CCd targets calculated from APd measured by laser meter were shallower than the guideline-recommended CCd. Further studies including evaluating hemodynamics during cardiopulmonary resuscitation with these shallower CCd targets are needed.

Abstract 14213: Injury Characteristics of Chest Compressions in a Swine Model of Infant Asphyxial Cardiac Arrest Using Either 1.5 inch or 1/3 Anterior-Posterior Diameter Depth Targets

Background: Current AHA guidelines for the delivery of chest compressions (CC) for infants and children are largely consensus based, and recommended depths of 1.5 inches or 1/3 anterior-posterior chest diameter (APD). It is unclear whether these have equal potential for injury. Objectives: We sought to examine and compare injury characteristics of CC delivered at 1.5 inches or 1/3 APD in an infant-sized model of asphyxial OHCA. Methods: Thirty-six juvenile swine weighing 10.6kg +/- 0.84 (approximating the 50 th percentile for a 12-month-old) were anesthetized, paralyzed, intubated, and mechanically ventilated (FiO2 21%). APD was measured and by two investigators via a sliding T-square. After instrumentation, the endotracheal tube was manually occluded to induce asphyxia, and occlusion was maintained for 9 minutes. Animals with an organized rhythm after 8 minutes 45 seconds of asphyxia received a single, 3-second transthoracic shock to induce ventricular fibrillation. At 9 minutes, each was then randomized to receive CC with a depth of 1.5 inches (Group 1) or 1/3 APD (Group 2), both with a rate of 100 per minute. ALS drugs were administered after 13 minutes, followed by initial defibrillation attempt at 14 minutes. Resuscitation continued until return of spontaneous circulation (ROSC) or 20 minutes of failed resuscitation. Survivors were sacrificed with KCl after 20 minutes of observation. Veterinary staff blinded to group assignment conducted necropsies to assess lung injury, rib fracture, hemothorax, airway bleeding, great vessel dissection, and heart/liver/spleen contusion. Characteristics were compared via Chi-Squared test or Mann-Whitney U-test using an alpha = 0.05. Results: Group 1 had n=18 and Group 2 had n=18 animals. Mean (SD) APD overall was 5.58 (0.22) inches, yielding a mean 1/3 APD depth of 1.86 inches. APD did not differ between groups. ROSC rates did not differ between groups (Group 1: 66.7% vs Group 2: 83.33%; p = 0.248. No injury characteristics differed significantly between groups. Airway bleeding rates were noteworthy though not different between groups (Group 1: 18.8% vs Group 2: 42.1%; p = 0.219). Conclusions: In a swine model of infant OHCA and resuscitation, both CC depth strategies had similar injury characteristics.

Abstract 324: Assessment of Optimal Chest Compression Depth to Optimize Cardiopulmonary Resuscitation: A Randomized Controlled Trial

Introduction: Neonatal chest compression (CC) should be performed to a 1/3 anterior-posterior (AP) chest diameter depth, however, the optimal AP depth is unknown. Hypothesis: We hypothesized that in asphyxiated neonatal piglets a 40% AP depth compared to 1/3, or 1/4 AP depth will reduce time to achieve return of spontaneously circulation and improve survival. Methods: Newborn piglets (n=8/group) were anesthetized, intubated, instrumented, and exposed to 45-minute normocapnic hypoxia followed by asphyxia and cardiac arrest. Piglets were randomly allocated to four intervention groups (“AP 12.5% depth”, “AP 1/4 depth”, “AP 1/3 depth” or “AP 40% depth“). CCs were performed using an automated CC machine with a rate of 90/min. Hemodynamic and respiratory parameters were continuously measured. Results: Median (IQR) time to return of spontaneously circulation was 70 (60-117), 85 (72-90), 90 (90-130), and 600 (600-600) sec with AP 40% depth, AP 1/3 depth, AP 1/4 depth, AP 12.5% depth, respectively. No piglet in the AP 12.5% depth group achieved ROSC while the short-term survival (1h) in the other groups was 100%. Systolic and diastolic blood pressure, central venous pressure, carotid blood flow, tidal volume, and minute ventilation increased with increasing AP depth. Conclusions: Time to return of spontaneously circulation and survival was similar between 1/4, 1/3, and 40% AP depth, while 12.5% AP depth did not result in return of spontaneously circulation. Hemodynamic and respiratory parameters improved with increasing AP depth suggesting that 40% AP depth might provide improved organ perfusion and oxygen delivery.

Abstract 215: Hemodynamics of Absolute, Proportional, and Adaptive Mechanical Chest Compression Strategies in a Swine Model of Pediatric Out-Of-Hospital Cardiac Arrest

Background: Guidelines for pediatric resuscitation recommend a depth of 1.5in or 1/3 anterior-posterior chest diameter for chest compressions (CC) despite little supporting evidence. Objective: To evaluate the hemodynamic effects of the two recommended depths and an adaptive strategy. Methods: Thirty-eight animals (mass ~25kg) were sedated, anesthetized, intubated, and ventilated. Micromanometer pressure sensors were installed in the aorta and right atrium via the right femoral artery and vein. Coronary perfusion pressure (CPP) was calculated as aortic minus right atrial pressure. An ultrasonic flow probe was secured around the right common carotid. Biosignals were recorded at 1000Hz. Animals were then re-paralyzed, followed by a fentanyl bolus, and the endotracheal tube was occluded for 9min. Each was randomized to absolute (Group 1: 1.5in & 100/min), proportional (Group 2: 1/3 AP diameter & 100/min), or stepwise adaptive (Group 3: 1.5in & 100/min, adding 0.25in or 5/min q25s until CPP > 25mmHg) CC using a robotic compressor. Epinephrine (0.1mg/kg) and sodium bicarbonate (1mEq/kg) were given after 4min, followed by epinephrine (0.15mg/kg) q3min. Defibrillation (150J) was attempted after 5min; CPR discontinued after 20min. Mean arterial pressure (MAP), CPP and carotid blood flow (CBF) were calculated for the first 10 minutes of CPR and compared between groups with generalized estimating equations (GEE). Results: In GEE models, MAP, CBF and CPP did not differ between groups over the first 10 minutes of resuscitation. Each measure differed significantly over time (p<0.05). When considering only the first 5 minutes (early phase including first pressor), hemodynamic variables also did not differ. Conclusion: In a swine model of asphyxial cardiac arrest, CC methods based on current guidelines and an additional adaptive approach did not differ hemodynamically.

The mechanism of blood flow during chest compressions for cardiac arrest is probably influenced by the patient's chest configuration.

AimMechanical assist devices are sometimes needed during resuscitation efforts of patients with prolonged cardiac arrest. Two such devices, the AutoPulse and the LUCAS, have different mechanisms of action. We propose that the effectiveness of mechanical assist devices is somewhat dependent on the configuration and compliance of the patient's chest wall.MethodsA previous study of patients with out‐of‐hospital cardiac arrest in Arizona reported that survivors were younger and many were observed to have narrow anterior–posterior chest diameters. These observations suggest that the predominant mechanism of blood flow during cardiopulmonary resuscitation of individuals with primary cardiac arrest is influenced by the patient's anterior–posterior chest diameter and compliance. It is proposed that in older individuals with an increased anterior–posterior chest diameter and decreased chest compliance that the AutoPulse, which works by increasing intrathoracic pressures, may be more effective. In contrast, the LUCAS device, which works predominately by compression of the sternum, is probably more effective in patients with narrower anterior–posterior diameters and a more compliant chest.ResultsThese hypotheses need to be confirmed by researchers who not only have access to the lateral chest roentgenograms of patients with cardiac arrest, to determine their anterior–posterior chest diameter, but also to the type of mechanical device that was used during resuscitation efforts and their patient's survival. If the observations herein proposed are confirmed, hospitals and paramedics may ideally need to have one of each type of mechanical chest compression unit and select the one to use depending on the patient's age and anterior–posterior chest diameter.ConclusionsThe mechanism of blood flow in patients with cardiac arrest is predominantly secondary to cardiac compression in younger patients with narrow anterior chest diameters and predominately secondary to the thoracic pump mechanism in older patients with emphysema.

A hemodynamic-directed approach to pediatric cardiopulmonary resuscitation (HD-CPR) improves survival

AimMost pediatric in-hospital cardiac arrests (IHCAs) occur in ICUs where invasive hemodynamic monitoring is frequently available. Titrating cardiopulmonary resuscitation (CPR) to the hemodynamic response of the individual improves survival in preclinical models of adult cardiac arrest. The objective of this study was to determine if titrating CPR to systolic blood pressure (SBP) and coronary perfusion pressure (CoPP) in a pediatric porcine model of asphyxia-associated ventricular fibrillation (VF) IHCA would improve survival as compared to traditional CPR. MethodsAfter 7min of asphyxia followed by VF, 4-week-old piglets received either hemodynamic-directed CPR (HD-CPR; compression depth titrated to SBP of 90mmHg and vasopressor administration to maintain CoPP ≥20mmHg); or Standard Care (compression depth 1/3 of the anterior–posterior chest diameter and epinephrine every 4min). All animals received CPR for 10min prior to the first defibrillation attempt. CPR was continued for a maximum of 20min. Protocolized intensive care was provided to all surviving animals for 4h. The primary outcome was 4-h survival. ResultsSurvival rate was greater with HD-CPR (12/12) than Standard Care (6/10; p=0.03). CoPP during HD-CPR was higher compared to Standard Care (point estimate +8.1mmHg, CI95: 0.5–15.8mmHg; p=0.04). Chest compression depth was lower with HD-CPR than Standard Care (point estimate −14.0mm, CI95: −9.6 to −18.4mm; p<0.01). Prior to the first defibrillation attempt, more vasopressor doses were administered with HD-CPR vs. Standard Care (median 5 vs. 2; p<0.01). ConclusionsHemodynamic-directed CPR improves short-term survival compared to standard depth-targeted CPR in a porcine model of pediatric asphyxia-associated VF IHCA.

Are the current guideline recommendations for neonatal cardiopulmonary resuscitation safe and effective?

A recently published review of approaches to optimize chest compressions in the resuscitation of asphyxiated newborns discussed the current recommendations and explored potential determinants of effective neonatal cardiopulmonary resuscitation (CPR). However, not all potential determinants of effective neonatal CPR were explored. Chest compression shallower than the current guideline recommendation of approximately 33% of the anterior-posterior (AP) chest diameter may be safer and more effective. From a physiological standpoint, high-velocity brief duration shallower compression may be more effective than current recommendations. The application of a 1- or 2-finger method of high-impulse CPR, which would depend on the size of the subject, may be more effective than using a 2-thumb (TT) encircling hands method of CPR. Adrenaline should not be used in the treatment of asphyxiated neonates and when necessary titrated vasopressin should be used.

Prognostic clinical indicators of short-term survival for ineffective breathing pattern in children with acute respiratory infection.

To identify prognostic clinical indicators of short-term survival for ineffective breathing pattern in children with acute respiratory infection. Despite the studies of survival for nursing diagnosis, there is not enough evidence about the clinical indicators that are associated with a worse prognosis for ineffective breathing pattern. A prospective cohort study. One hundred and thirty-six children were followed up for a minimum of six and a maximum of 10 consecutive days. The survival rate for ineffective breathing pattern was calculated using Nelson-Aalen's method. An extended Cox model was adjusted to identify the main prognostic clinical indicators for this nursing diagnosis. Over half of the sample had an ineffective breathing pattern at the first evaluation. The occurrence of new cases was observed until the ninth day of monitoring, and the survival rate after this day was low. According to the Cox model, the main clinical indicators of a poor prognosis were an abnormal breathing pattern, the use of accessory muscles, dyspnoea and increase in the anterior-posterior chest diameter. Children with acute respiratory infection who present with an abnormal breathing pattern, the use of accessory muscles to breathe, dyspnoea and increased anterior-posterior diameter have a poor prognosis for an ineffective breathing pattern. Survival analyses of nursing diagnoses allow the identification of clinical indicators that can be used in clinical practice as prognostic markers. The identification of indicators associated with a poor clinical prognosis allows nurses to intervene early and to maximise the possibility of a good outcome.

A new chest compression depth indicator would increase compression depth without increasing overcompression risk

PurposeAdequate chest compression (CC) depth is critical for effective cardiopulmonary resuscitation. Pediatric resuscitation guidelines recommend that CC be at least one-third of the anterior-posterior (AP) chest diameter or approximately 4 cm in infants and 5 cm in children. We aimed to find a better indicator of CC depth that maximizes CC depth while also minimizing injury. Basic proceduresChest computed tomographic images of patients aged 8 years and younger were measured for external diameter (ED) (AP distance from skin to skin) and internal diameter (AP distance between internal surface of anterior chest wall and anterior surface of vertebral body) at the midway of the lower half of the sternum. Compressible depth was defined as 1 cm short of internal diameter. We determined that up to a 10% estimated risk of overcompression is acceptable and approximated a quantile regression line for the 10th percentile of compressible depth on ED. After rounding coefficients, we used its equation as a new indicator. Main findingsA total of 426 images were analyzed. The new indicator had a slope of 0.5 and an intercept of −1.9 cm (1 fingerbreadth). Compared to one-third ED, the new indicator would provide deeper CC with average difference of 1.9 mm (95% confidence interval, 1.6-2.2 mm) without increasing the risk of overcompression (both 4.9%). Chest compression of 4/5 cm would provide deeper CC compared to the new indicator (difference, 3.5 mm; 95% confidence interval, 2.7-4.1 mm); however, its overcompression risk was too high (31.5%). Principal conclusionChest compression of one-half ED minus 1 fingerbreadth maximizes CC depth without increasing overcompression in pediatric population.

Compression rate of infant CPR in three positions

Purpose: The recently published guidelines by the European Resuscitation Council (ERC) still focus on high-quality chest compressions to minimise no-flow periods in paediatric life support. In infants compression depth should achieve at least 1/3 of the anterior–posterior chest diameter with a compression rate of at least 100 but no greater than 120min. Published figures of infant resuscitation assume the supine position to be the recommended one. Besides this, other positions were published1 or mentioned by paediatricians, but have not yet been evaluated in respect to quality of cardiopulmonary resuscitation (CPR).

Use of the anterior-posterior chest diameter in CT: reduction in radiation dose?

Use of the anterior-posterior chest diameter in CT: reduction in radiation dose?

Radiation dose optimisation in dynamic volume CT of the heart: tube current adaptation based on anterior–posterior chest diameter

To compare tube current adaptation based on 3 body mass index (BMI) categories versus anterior-posterior chest diameter (APD) for radiation dose optimisation in patients undergoing dynamic volume cardiac CT. Two cardiac imaging centres participated in the study. 20 patients underwent a prospectively triggered 320-slice single beat cardiac CT using the X-ray tube current [mA] manually adjusted to the patient's BMI (group I). In 20 subsequent patients, the tube current was adapted according to the patient's APD (group II). All other parameters were kept constant. Image noise was defined as the standard deviation of attenuation values and measured using a ROI in the descending aorta. Variation in image noise was statistically compared between both patient groups. Average and standard deviation of pixel noise were 29.1 HU and 14.8 HU in group I and 28.0 HU and 4.2 HU in group II. Inter-individual variation of pixel noise was significantly lower in group II compared to group I (p < 0.0001). Tube current adaptation based on APD is superior to stepwise adaptation based on BMI for optimising radiation dose in dynamic volume cardiac CT and therefore limits unnecessary radiation dose while ensuring diagnostic image quality in patients with diverse body habitus.

Depth of sternal compression and intra-arterial blood pressure during CPR in infants following cardiac surgery

The optimal depth of sternal compressions during cardiopulmonary resuscitation (CPR) in infants is unknown; current guidelines recommend compressing to a depth of 1/3rd to 1/2 the anterior-posterior (AP) diameter of the chest. Our experience to compress the chest at 1/3rd the AP diameter often fails to provide an adequate blood pressure response. We reviewed our experience with CPR, depth of compressions, and arterial blood pressure response in a cohort of 6 infants having cardiac surgery and subsequent cardiac arrest. Pediatric advanced life support measures were initiated, with attempted compressions to 1/3rd the AP chest diameter. Depth of attempted compressions was increased to approximately 1/2 the AP chest diameter if systolic BP response was inadequate (i.e., <60 mm Hg systolic). BP tracings were reviewed and contiguous recordings were evaluated as compressions were attempted at 1/3rd and 1/2 the AP chest diameter. The age range was from 2 weeks to 7.3 months, and median age was of 1.0 month. The mean systolic BP was 83.4 mm Hg for the 1/2 AP chest diameter technique vs. 51.6 mm Hg for the 1/3rd AP diameter approach, p < 0.001. The mean diastolic pressure was similar with both strategies (30.5 vs. 30.6 mm Hg, p = 0.99). In this cohort of 6 infants having cardiac surgery and subsequent cardiac arrest, attempting to compress the chest at 1/2 the AP diameter increased systolic blood pressure by 62% compared to attempting to compress 1/3rd the AP diameter. Perhaps resuscitators should attempt to compress infants’ chests 1/2 rather than 1/3rd the AP diameter of the chest.

Radiological assessment of the paediatric chest: Need for revising current guidelines for chest compression?

Introduction: The current guidelines on neonatal and paediatric resuscitation recommend a compression depth of 1/3 to 1/2 of the anterior–posterior chest diameter (APD). However, there has been little evidence supporting such manoeuvre. This study was conducted to assess the actual depth of chest compressions in neonatal and paediatric populations if current guidelines are strictly followed.

Radiological assessment of the adult chest: Implications for chest compressions

The recommended depth for chest compression during adult cardiopulmonary resuscitation (CPR) is 4-5 cm, and for children one-third the anterior-posterior (AP) chest diameter. A compression depth of one-third of the AP chest diameter has also been suggested for adult CPR. We have assessed chest CT scans to measure what proportion of the adult AP chest diameter is compressed during CPR. Measurements of AP diameter of chest CT scans were taken from the skin anteriorly at the middle of the lower half of the sternum, perpendicularly to the skin on the posterior thorax. The anatomical structure that would be compressed at this level was also noted. One hundred consecutive CT scans were examined (66 males and 34 females). The age (mean +/- S.D.) was 68+/-12 years. AP chest diameter was 253 +/- 27 mm for males and 235 +/- 30 mm for females. The proportion of total AP chest diameter compressed with current compressions is 15.8-19.8% for males and 17.0-21.3% for females. The commonest anatomical structures that would be compressed are the ascending aorta (38%) and the top of the left atrium (36%). There is also a wide anatomical variation in the shape of the adult chest. A chest compression depth of 4-5 cm in adults equates to approximately one-fifth of the AP diameter of the adult chest.

Quantitative dysmorphology assessment in Fabry disease

Purpose: 1) To identify morphometric characteristics in hemizygous patients with Fabry disease a treatable lysosomal storage disorder caused by the deficiency of α-galactosidase A where morphological abnormalities have occasionally been mentioned, but have never been investigated systematically. 2) To devise a quantitative method to evaluate dysmorphic abnormalities in Fabry disease.Method: Cross-sectional, single center, independent dysmorphology assessment by a panel of three clinical geneticists, based on standardized medical photography. Population: consecutive hemizygous patients with Fabry disease (N = 38) unselected for the features assessed, mean age 38 ± 10.8 years (range: 10–60), recruited for neuropathic pain into enzyme replacement therapy trials.Results: The following dysmorphic features were identified (in order of descending frequency): periorbital fullness, prominent lobules of the ears, bushy eyebrows, recessed forehead, pronounced nasal angle, generous nose/bulbous nasal tip, prominent supraorbital ridges, shallow midface, full lips, prominent nasal bridge, broad alar base, coarse features, posteriorly rotated ears, and prognathism. Extremity features included broad fingertips, short fingers, prominent superficial vessels of hands, 5th digit brachydactyly, and 5th digit clinodactyly. Narrow anterior-posterior chest diameter was noted. Ten core features were statistically defined. Cronbach's alpha measuring internal consitency was 0.62. Light's kappa for global inter-rater variability was 0.26 while Cohen's kappa allowing pair-wise rater comparison varied between 0.08–0.48.Conclusions: Patients with Fabry disease share common morphological characteristics of the face, trunk, and extremities. Some of these features are subtle as documented by the inter-rater variability. Awareness of these features may facilitate the diagnosis of patients with Fabry disease, and identification of affected family members.

Anatomically and Physiologically Based Reference Level for Measurement of Intracardiac Pressures

Many reference levels have been proposed for the measurement of intracardiac pressures, but none have met with universal acceptance. In the first part of our study, we evaluated 10 cardiologists' understanding of how hydrostatic pressure influences intracardiac pressures as measured with fluid-filled catheters. In the second part, we proposed and validated a new zero level (H): the uppermost blood level in the left ventricular (LV) chamber relative to the anterior chest wall for a patient in the supine position. A comparison was made of LV minimum diastolic pressure measured by reference to H versus measurements made with the zero level at midchest. Using two-dimensional echocardiography, we determined H in the LVs of seven normal patients (five male, two female; age, 49 +/- 9 years) undergoing routine cardiac catheterization. H was determined from a left parasternal short-axis view and calculated as the average distance between end diastole and end systole of the endocardium of the uppermost segment of the LV anterior wall below the fourth or fifth intercostal space of the left sternal border on the anterior surface of the chest wall, with the patient in the supine position. A micromanometer/fluid-filled lumen catheter was then positioned in the LV, and we compared the micromanometer LV minimum pressure (LVPmin) obtained when the reference fluid-filled transducer was aligned at midchest with the LVPmin obtained when the reference fluid-filled transducer was aligned at H. LVPmin referenced to a midchest fluid-filled external transducer was measured as 5.1 +/- 1.6 mm Hg (range, 2.4 to 7.2 mm Hg) versus -0.6 +/- 0.6 mm Hg (range, -1.6 to 0.4 mm Hg) when referenced to H (P < .001). A significant linear relation was found to exist between patient anterior-posterior chest diameter and the magnitude of hydrostatic pressure influences related to pressure referenced at midchest (r = .88; P < .01). External fluid-filled transducers should be used with the goal of removing hydrostatic pressure and other influences so that the presence of subatmospheric pressure during diastole in any of the cardiac chambers is accurately measured. To achieve this goal, intracardiac pressure should be referenced to an external fluid-filled transducer aligned with the uppermost blood level in the chamber in which pressure is to be measured. The current practice of referencing the zero level of LV diastolic pressure to an external fluid-filled transducer positioned at the midchest level results in systematic overestimation due to hydrostatic effects and produces physiologically significant error in the measurement of diastolic intracardiac pressure.

The optimal technique for electrical cardioversion of atrial fibrillation

The optimal approach to electrical cardioversion of atrial fibrillation includes appropriate patient selection, anticoagulation, careful selection and monitoring of antiarrhythmic therapy, and proper electrical cardioversion technique. The optimal technique requires the use of metal electrodes, with one electrode of at least 8 cm in diameter placed in the anterior position, and the second of 12-13 cm diameter placed posteriorly just below the left scapulae, with generous amounts of the appropriate gel (such as Hewlett-Packard Redux Paste) as the electrode-skin interface and firm pressure to the paddle electrode with the patient in expiration. Thus the anterior-posterior chest diameter is decreased and less air between the electrodes is assured. The initial shock strength should be 200 J. The shock is synchronized with the electrocardiographic QRS complex. This report reviews the justification for these recommendations.

Echocardiographic assessment of mitral valve function during mechanical cardiopulmonary resuscitation in pigs

Using two-dimensional and M-mode echocardiography, mitral valve function was assessed during mechanical cardiopulmonary resuscitation (CPR). In 10 anesthetized pigs CPR began 1 min after induction of ventricular fibrillation; in all pigs three different compressive forces (200, 350, and 500 Newton [N]) were applied in randomized sequence for 3 min each, thus resulting in a reduction of anterior-posterior chest diameter by 15%, 20%, and 25%, respectively. Echocardiographic recordings of adequate technical quality were obtained from seven animals. During ventricular fibrillation, mitral valve leaflets showed fibrillatory movements without closure. During CPR systole with a compressive force of 200 N, the mitral valve closed in 114 of 700 CPR cycles (16%). This rate increased significantly (P less than 0.001) to 399 of 584 cycles (68%) with 350 N, and further to 470 of 494 cycles (95%) with 500 N. The higher mitral valve closure incidence was linked to statistically significant increases in systolic cerebral (+125%) and diastolic myocardial perfusion pressures (+136%) and cardiac output. We thus conclude that with low compressive force blood flow during mechanical CPR is due mainly to the chest pump mechanism, whereas the cardiac pump mechanism is effective with high compressive forces.