Ventricular fibrillation: basic concepts

Atrioventricular conduction abnormalities are associated with poor outcome following intermittent umbilical cord occlusions in fetal sheep

INTRODUCTION

Fetal arrhythmias have been described with intrapartum hypoxemia; however, they cannot be accurately diagnosed with currently used fetal heart rate (FHR) monitoring systems due to low resolution and signal averaging. We used a Holter device to record electrocardiogram (ECG) at 250 Hz in term sheep fetuses that developed severe metabolic acidosis induced by intermittent umbilical cord occlusions (UCOs), mimicking human labor contractions. We hypothesized that UCOs leading to worsening fetal metabolic acidosis provoke distinct fetal arrhythmias that could indicate impending fetal death.

MATERIAL AND METHODS

Thirteen pregnant sheep (gestational age 133-135/145 days) were instrumented under general anesthesia. Three electrodes were placed on the fetal chest and connected to a Holter device for continuous ECG recording at a sampling rate of 250 Hz. The fetal axillary artery was catheterized and an inflatable occluder was placed around the umbilical cord. After a 4-5 day recovery, complete UCOs were induced by inflating the occluder for 1 min, followed by deflation for 2 min, until the fetal arterial pH dropped <7.0 and/or base excess (BE) <-16. Thereafter, an emergency cesarean section was performed to deliver the fetus.

RESULTS

Eight sheep fetuses were included in the final analysis. All fetuses had normal baseline arterial blood gases and lactate values. During the first two UCOs, all fetuses demonstrated isolated benign arrhythmias. Three fetuses that developed severe metabolic acidosis after five UCOs showed persistent atrioventricular (AV) conduction abnormalities during the last UCO and its release, requiring cardiopulmonary resuscitation (CPR) at birth. One fetus with third-degree AV block had no detectable QRS complexes at birth, developed ventricular tachycardia and fibrillation (VT/VF) during CPR, and was successfully defibrillated. Five fetuses tolerated ≥10 UCOs before developing severe metabolic acidosis, and none of these showed any persistent AV-conduction abnormalities, though one fetus died after developing VT/VF after the 10th UCO.

CONCLUSIONS

Metabolic acidemia induced by intermittent UCOs in term sheep fetuses is associated with various arrhythmias, some of which may be life-threatening. Continuous intrapartum fetal ECG recording at a sample rate of ≥250 Hz coupled with a software capable of automatically detecting significant arrhythmias could enhance intrapartum fetal monitoring in the future.

Significance of automated external defibrillator in identifying lethal ventricular arrhythmias

Automated electrical defibrillator (AED) is critical in saving children who develop unexpected cardiac arrest (CA), but its diagnostic capacity is not fully acknowledged. Retrospective cohort study of patients with aborted sudden cardiac death (SCD) was performed. Twenty-five patients (14 males) aged 1.3 to 17.5 years who presented with CA survived with prompt cardiopulmonary resuscitation. Eighteen patients had no prior cardiac diagnosis. Cardiac arrest occurred in 10 patients with more than moderate exercise, in 7 with light exercise, and in 8 at rest (including one during sleep). Twenty-two patients were resuscitated with AED, all of which were recognized as a shockable cardiac rhythm. Thorough investigations revealed 6 ion channelopathies (4 catecholaminergic polymorphic ventricular tachycardia, one long QT syndrome, and one Brugada syndrome), 5 congenital heart disease (including 2 with coronary artery obstruction), 6 cardiomyopathies, 2 myocarditis, and 2 miscellaneous. Four patients had no identifiable heart disease. In 5 patients, the downloaded AED-recorded rhythm strip delineated the underlying arrhythmias and their responses to electrical shocks. Four patients who presented with generalized seizure at rest were initially managed for seizure disorder until AED recording identified lethal ventricular arrhythmias.Conclusions: AED reliably identifies the underlying lethal ventricular arrhythmias in addition to aborting SCD. What is Known: • Although infrequent in children, sudden cardiac death (SCD) is often an unexpected and tragic event. The etiology is diverse and sometimes remains unknown despite extensive investigations. • Automated external defibrillator (AED) is both therapeutic in aborting SCD and diagnostic in identifying the underlying lethal ventricular arrhythmias. However, the diagnostic aspect of AED is under-acknowledged by most medical providers. What is New: • Four of 25 patients (16%) were initially managed for possible seizure disorders until AED recording identified lethal ventricular arrhythmia. • The AED recording of the lethal arrhythmia during cardiopulmonary resuscitation (CPR) should always be obtained as it plays a crucial role in the decision-making process before ICD implantation. All medical providers should become familiar with downloading cardiac rhythm strips from AED when requested.

Demographics, bystander CPR, and AED use in out-of-hospital pediatric arrests

BACKGROUND

In 2005 the American Heart Association released guidelines calling for routine use of automated external defibrillators during pediatric out-of-hospital arrest. The goal of this study was to determine if these guidelines are used during resuscitations.

METHODS

We conducted a secondary analysis of prospectively collected data from 29 U.S. cities that participate in the Cardiac Arrest Registry to Enhance Survival (CARES). Patients were included if they were older than 1 year of age and had a documented resuscitation attempt from October 1, 2005 through December 31, 2009 from an arrest presumed to be cardiac in nature. Hierarchical multivariable logistic regression analysis was used to estimate the associations between age, demographic factors, and AED use.

RESULTS

129 patients were 1-8 years of age (younger children), 88 patients were 9-17 years of age (older children), and 19,338 patients were ≥18 years of age (adults). When compared to adults, younger children were less likely to be found in a shockable rhythm (young children 11.6%, adults 23.7%) and were less likely to have an AED used (young children 16.3%, adults 28.3%). Older children had a similar prevalence of shockable rhythms as adults (31.8%) and AED use (20.5%). A multivariable analysis demonstrated that, when compared to adults, younger children had decreased odds of having an AED used (OR 0.42, 95% CI 0.26-0.69), but there was no difference in AED use among older children and adults.

CONCLUSIONS

Young children suffering from presumed out-of-hospital cardiac arrests are less likely to have a shockable rhythm when compared to adults, and are less likely to have an AED used during resuscitation.

Effect of sildenafil citrate on the cardiovascular system

Sildenafil citrate is a drug commonly used to manage erectile dysfunction. It is designated chemically as 1-[[3-(6,7-dihydro-1-methyl-7-oxo-3-propyl-1H -pyrazolo[4,3-d]pyrimidin-5-yl)-4 ethoxyphenyl] sulfonyl]-4-methylpiperazine citrate (C22H30N6(O4)S). It is a highly selective inhibitor of cyclic guanine monophosphate-specific phosphodiesterase type 5. In late March through mid-November 1998, the US Food and Drug Administration (FDA) published a report on 130 confirmed deaths among men (mean age, 64 years) who received prescriptions for sildenafil citrate, a period during which >6 million outpatient prescriptions (representing about 50 million tablets) were dispensed. The US FDA recently reported that significant cardiovascular events, including sudden cardiac death, have occurred in men with erectile dysfunction who were taking sildenafil citrate. These reports have raised concerns that sildenafil citrate may increase the risk of cardiovascular events, particularly fatal arrhythmias, in patients with cardiovascular disease. In the past few years, the cardiac electrophysiological effects of sildenafil citrate have been investigated extensively in both animal and clinical studies. According to extensive data available to date, sildenafil citrate has been shown to pose minimal cardiovascular risks to healthy people taking this drug. Some precautions are needed for patients with cardiovascular diseases. However, the only absolute contraindication for sildenafil citrate is the concurrent use of nitrates. This article is intended to review sildenafil citrate's cardiovascular effects, as well as current debates about its arrhythmogenic effects.