Value and limitations of adenosine in the diagnosis and treatment of narrow and broad complex tachycardias

Adenosine in Interventional Cardiology: Physiopathologic and Pharmacologic Effects in Coronary Artery Disease

This review article focuses on the role of adenosine in coronary artery disease (CAD) diagnosis and treatment. Adenosine, an endogenous purine nucleoside, plays crucial roles in cardiovascular physiology and pathology. Its release and effects, mediated by specific receptors, influence vasomotor function, blood pressure regulation, heart rate, and platelet activity. Adenosine therapeutic effects include treatment of the no-reflow phenomenon and paroxysmal supraventricular tachycardia. The production of adenosine involves complex cellular pathways, with extracellular and intracellular synthesis mechanisms. Adenosine's rapid metabolism underscores its short half-life and physiological turnover. Furthermore, adenosine's involvement in side effects of antiplatelet therapy, particularly ticagrelor and cangrelor, highlights its clinical significance. Moreover, adenosine serves as a valuable tool in CAD diagnosis, aiding stress testing modalities and guiding intracoronary physiological assessments. Its use in assessing epicardial stenosis and microvascular dysfunction is pivotal for treatment decisions. Overall, understanding adenosine's mechanisms and clinical implications is essential for optimizing CAD management strategies, encompassing both therapeutic interventions and diagnostic approaches.

Dual Atrioventricular Nodal Non-Reentrant Tachycardia Misdiagnosed as Rapid Atrial Fibrillation - The Role of Adenosine

We report a case of a 56-year-old man diagnosed with non-ischemic cardiomyopathy in 2017 with progressive decline in left ventricular systolic function and frequent hospitalisations for heart failure in the context of a presumed atrial fibrillation with high ventricular rate. Electrocardiographic changes after adenosine administration raised the suspicion of dual atrioventricular nodal non-reentrant tachycardia, a diagnosis that was confirmed by electrophysiological study, making adenosine a potential diagnostic aid in such cases. The ablation of the slow pathway terminated the tachycardia and led to a marked improvement in symptomatology and echocardiographic parameters.

Management of tachyarrhythmias in pregnancy - A review

The most common arrhythmias detected during pregnancy include sinus tachycardia, sinus bradycardia, and sinus arrhythmia, identified in 0.1% of pregnancies. Isolated premature atrial or ventricular arrhythmias are observed in 0.03% of pregnancies. Arrhythmias may become more frequent during pregnancy or may manifest for the first time.

Low-dose adenosine-induced transient asystole during intracranial aneurysm surgery

Background

Few studies have evaluated the adenosine dose that induces cardiac arrest during intracranial aneurysm surgery. We present our experiences with adenosine-induced transient asystole (AiTA) during intracranial aneurysm surgery and dosage recommendations.

Methods

We retrospectively reviewed the medical records of all patients who underwent intracranial aneurysm surgery between July 2016 and December 2018. Patients who experienced AiTA during intracranial aneurysm surgery were included in the study.

Results

Our study included nine intracranial aneurysm surgeries performed in eight patients. Thirteen episodes of AiTA were reported. Five of these were performed to facilitate bleeding control due to intraoperative aneurysm rupture (IAR), and adenosine doses were 9 mg (0.20 mg/kg), 12 mg (0.25 mg/kg), 12 mg (0.26 mg/kg), 18 mg (0.34 mg/kg), and 18 mg (0.39 mg/kg), resulted in transient asystole for 12, 14, 9, 44, and 18 s, respectively. For episodes without IAR, adenosine doses ranging from 6 to 18 mg (0.11-0.39 mg/kg) caused asystole for 8-33 s. In five episodes without IAR, low-dose adenosine (lower than 0.2 mg/kg) was used and caused asystole ranging from 8 to 12 s. Postoperatively, two patients had elevated cardiac troponin T levels but normal electrocardiograms.

Conclusion

AiTA can facilitate the clipping of intracranial aneurysms at low-risk of serious cardiac complications. An adenosine dose of 0.2-0.4 mg/kg is safe and effective in both IAR and non IAR situations. In non IAR cases, we propose that low-dose AiTA is an option to facilitate aneurysm clipping. A starting dose of 6 mg or 0.1-0.2 mg/kg can adequately induce brief asystole by softening the aneurysmal sac during clip application.

Supraventricular tachycardia: An overview of diagnosis and management

Supraventricular tachycardia (SVT) is a common cause of hospital admissions and can cause significant patient discomfort and distress. The most common SVTs include atrioventricular nodal re-entrant tachycardia, atrioventricular re-entrant tachycardia and atrial tachycardia. In many cases, the underlying mechanism can be deduced from electrocardiography during tachycardia, comparing it with sinus rhythm, and assessing the onset and offset of tachycardia. Recent European Society of Cardiology guidelines continue to advocate the use of vagal manoeuvres and adenosine as first-line therapies in the acute diagnosis and management of SVT. Alternative therapies include the use of beta-blockers and calcium channel blockers. All patients treated for SVT should be referred for a heart rhythm specialist opinion. Long-term treatment is dependent on several factors including frequency of symptoms, risk stratification, and patient preference. Management can range from conservative, if symptoms are rare and the patient is low risk, to catheter ablation which is curative in the majority of patients.

Cardiovascular effects of two adenosine constant rate infusions in anaesthetized dogs

OBJECTIVE

Adenosine induces vasodilatation. The aim of this study was to investigate cardiovascular effects of two adenosine constant rate infusion (CRI) doses in dogs.

STUDY DESIGN

Experimental, longitudinal repeated measure design.

ANIMALS

Ten healthy purpose-bred Beagle dogs.

METHODS

Each dog was sedated with butorphanol. Anaesthesia was induced with propofol intravenously and maintained with sevoflurane (inspired oxygen fraction = 47-55%). Controlled mechanical ventilation was used to maintain normocapnia. Two doses of adenosine were administered as CRIs to each dog: 140 μg kg^-1 minute^-1 (A140) followed by 280 μg kg^-1 minute^-1 (A280). Pulse rate, invasive arterial pressure and stroke volume (by magnetic resonance phase contrast angiography) were measured at baseline, 3 minutes after starting adenosine and 3 and 10 minutes after discontinuing adenosine. Cardiac output, cardiac index and approximated systemic vascular resistances (approximate SVR) were calculated. Additionally, arterial blood gases, co-oximetry, electrolytes, glucose and lactate were measured and oxygen content and delivery calculated. One-way repeated measures analysis of variance (p < 0.05) was used for data analysis.

RESULTS

A140 and A280 resulted in a significant decrease in arterial blood pressure [systolic (p = 0.008), mean (p = 0.003), and diastolic arterial pressure (p = 0.004)] and approximate SVR (p = 0.008) compared with baseline. No significant changes were detected for the other variables. All values returned to baseline within 3 minutes after adenosine discontinuation.

CONCLUSIONS AND CLINICAL RELEVANCE

Adenosine CRI decreases arterial pressure by vasodilatation in healthy dogs. No additional effects were observed with the higher dose. The effects in compromised dogs remain to be investigated.

Adenosine Conversion of Supraventricular Tachycardia Associated with High-Dose Epinephrine Therapy for Cardiac Arrest

Adenosine has received wide acceptance as the drug of choice for initial treatment of supraventricular tachycardias (supraventricular tachycardia), and as a diagnostic adjunct in hemodynamically stable, wide-complex tachycardias. This report describes the successful use of adenosine for the treatment of supraventricular tachycardia occurring after successful initial resuscitation from ventricular fibrillation, in which a high dose of the epinephrine protocol was used.

Part 8: adult advanced cardiovascular life support: 2010 American Heart Association Guidelines for Cardiopulmonary Resuscitation and Emergency Cardiovascular Care

The goal of therapy for bradycardia or tachycardia is to rapidly identify and treat patients who are hemodynamically unstable or symptomatic due to the arrhythmia. Drugs or, when appropriate, pacing may be used to control unstable or symptomatic bradycardia. Cardioversion or drugs or both may be used to control unstable or symptomatic tachycardia. ACLS providers should closely monitor stable patients pending expert consultation and should be prepared to aggressively treat those with evidence of decompensation.

Adenosine for wide-complex tachycardia: efficacy and safety

OBJECTIVES

: To determine whether adenosine is useful and safe as a diagnostic and therapeutic agent for patients with undifferentiated wide QRS complex tachycardia. The etiology of sustained monomorphic wide QRS complex tachycardia is often uncertain acutely.

DESIGN

: A retrospective observational study.

SETTING

: Treatment associated with emergency visits at nine urban hospitals.

PATIENTS

: Consecutive patients treated with adenosine for regular wide QRS complex tachycardia between 1991 and 2006.

INTERVENTIONS

: Treatment with adenosine infusion.

MEASUREMENTS AND MAIN RESULTS

: Measured outcomes included rhythm response to adenosine, if any, and all adverse effects. A positive response was defined as an observed change in rhythm including temporary atrioventricular conduction block or tachycardia termination. A primary adverse event was defined as emergent electrical or medical therapy instituted in response to an adverse adenosine effect. A rhythm diagnosis was made in each case. The characteristics of adenosine administration as a test for a supraventricular as opposed to ventricular tachycardia were determined, and the adverse event rates were calculated. A total of 197 patients were included: 104 (90%) of 116 (95% confidence interval, 83%-95%) and two (2%) of 81 (95% confidence interval, 0.3%-9%) supraventricular tachycardia and ventricular tachycardia patients demonstrated a response to adenosine, respectively. The odds of supraventricular tachycardia increased by a factor of 36 (95% confidence interval, 9-143) after a positive response to adenosine. The odds of ventricular tachycardia increased by a factor of 9 (95% confidence interval, 6-16) when there was no response to adenosine. The rate of primary adverse events for patients with supraventricular tachycardia and ventricular tachycardia was 0 (0%) of 116 (95% confidence interval, 0%-3%) and 0 (0%) of 81 (95% confidence interval, 0%-4%), respectively.

CONCLUSIONS

: Adenosine is useful and safe as a diagnostic and therapeutic agent for patients with regular wide QRS complex tachycardia.

[Regular tachycardia with broad QRS complex: differential diagnosis on 12-lead ECG]

Differential diagnosis of regular tachycardia with broad QRS complex can be challenging in daily practice. There are four different arrhythmias that have to be taken into account when being confronted with a broad QRS complex tachycardia: (1) ventricular tachycardia (VT); (2) supraventricular tachycardia (SVT) with bundle branch block (BBB); (3) SVT with AV conduction over an accessory AV pathway; (4) paced ventricular rhythm. Due to potentially fatal consequences, the correct diagnosis is important in view of both the acute treatment and the long-term therapy. Since SVT with accessory conduction is rare and a paced ventricular rhythm can be identified easily by stimulation artifacts, in most cases, a VT has to be differentiated from an SVT with BBB. Several ECG criteria can be helpful: (1) QRS complex duration > 140 ms in right BBB tachycardia or > 160 ms in left BBB tachycardia; (2) ventricular fusion beats; (3)"Northwest" QRS axis; (4) ventriculoatrial dissociation; (5) absence of an RS complex or RS interval > 100 ms in leads V(1)-V(6); (6) a positive or negative concordant R wave progression pattern in leads V(1)-V(6); (7) absence of an initial R wave or an S wave in lead V(1) in right BBB tachycardia; (8) absence of an R wave or an R/S ratio < 1 in lead V(6) in right BBB tachycardia; (9) absence or delay of the initial negative forces in lead V(1) in left BBB pattern (R wave duration > 30 ms in V(1); interval between onset of R wave and Nadir of S wave > 60 ms in V(1)); (10) presence of Q wave. Any of these variables favor VT. However, none of the criteria has both a sufficient sensitivity and specificity when utilized on its own. Therefore, various diagnostic algorithms have been proposed using a number of the above criteria consecutively. By doing so, the specificity and sensitivity of correctly identifying a VT or an SVT with BBB can be raised to > 95%.

Adenosine-induced ventricular arrhythmias in patients with supraventricular tachycardias

BACKGROUND

Adenosine is widely used for the diagnosis and the termination of supraventricular arrhythmias. There are many case reports and few series about the proarrhythmic potential of adenosine. We sought to evaluate the proarrhythmic potential of adenosine used to terminate the supraventricular arrhythmias.

METHODS

The records of all patients that received adenosine for the termination of supraventricular tachycardia were reviewed retrospectively and those with a continuous electrocardiographic (ECG) recording during adenosine administration were included to the study.

RESULTS

Our search identified 52 supraventricular episodes of 46 patients with a continuous ECG recording during adenosine administration. Following adenosine administration, premature ventricular contraction (PVC) or ventricular tachycardia (VT) developed in 22 (47.8%) patients and in 26 (50%) tachycardia episodes. No patient had a sustained VT. Nonsustained VT developed in eight (17.4%) patients. All VT episodes were polymorphic, short, and self-terminating. When the basal and demographic properties of patients with PVC or VT and those without PVT or VT were compared, there was no significant difference.

CONCLUSIONS

Adenosine is a quite safe and effective drug for the termination of narrow QRS complex tachycardia but it often induces nonsustained VT or PVC that are clinically insignificant in the absence of other accompanying heart disease.

Intravenous ATP infusions can be safely administered in the home setting: a study in pre-terminal cancer patients

The aim of the study was to investigate the safety of adenosine 5′-triphosphate (ATP) administration at home in pre-terminal cancer patients. Included were patients with cancer for whom medical treatment options were restricted to supportive care, who had a life expectancy of less than 6 months, a World Health Organization performance status 1 or 2, and suffered from at least one of the following complaints: fatigue, anorexia or weight loss >5% over the previous 6 months. Side effects were registered systematically on a standard form according to the National Cancer Institute (NCI) Common Toxicity Criteria. Fifty-one patients received a total of 266 intravenous ATP infusions. Of these, 11 infusions (4%) were given at the lowest dose of 20 μg kg⁻¹ min⁻¹, 85 infusions (32%) at 25–40 μg kg⁻¹ min⁻¹, and 170 (64%) at the highest dose of 45–50 μg kg⁻¹ min⁻¹ ATP. The majority of ATP infusions (63%) were without side effects. Dyspnea was the most common side effect (14% of infusions), followed by chest discomfort (12%) and the urge to take a deep breath (11%). No symptoms of cardiac ischemia occurred in any of the infusions. All side effects were transient and resolved within minutes after lowering the ATP infusion rate. Side effects were most frequent in the presence of cardiac disorders. We conclude that ATP at a maximum dose of 50 μg kg⁻¹ min⁻¹ can be safely administered in the home setting in patients with pre-terminal cancer.

Proarrhythmic effects of adenosine: a review of the literature

Adenosine is widely used as an antiarrhythmic agent for the investigation and management of both narrow complex and, less often, broad complex tachycardias. Over the past 10 years or so, reports of severe bradycardias and tachyarrhythmias being induced by this agent have appeared in the literature. As adenosine is increasingly used in emergency departments and indeed outside the hospital setting, a greater awareness of these potential problems is important. In this paper the evidence for such effects is summarised, and the mechanisms involved discussed.

Potential value of adenosine 5'-triphosphate (ATP) and adenosine in anaesthesia and intensive care medicine

Extracellular adenosine and adenosine triphosphate (ATP) are involved in biological processes including neurotransmission, muscle contraction, cardiac function, platelet function, vasodilatation, signal transduction and secretion in a variety of cell types. They are released from the cytoplasm of several cell types and interact with specific purinergic receptors which are present on the surface of many cells. This review summarizes the evidence on the potential value and applicability of ATP (not restricted to ATP-MgCl(2)) and adenosine in the field of anaesthesia and intensive care medicine. It focuses, in particular, on evidence and roles in treatment of acute and chronic pain and in sepsis. Based on the evidence from animal and clinical studies performed during the last 20 years, ATP could provide a valuable addition to the therapeutic options in anaesthesia and intensive care medicine. It may have particular roles in pain management, modulation of haemodynamics and treatment of shock.

Possible therapeutic benefits of adenosine-potentiating drugs in reducing age-related degenerative disease in dogs and cats

Adenosine is a ubiquitous, biologically important molecule that is a precursor of other biologically active molecules. It also is a component of some co-factors and has distinct physiological actions in its own right. Levels are maintained by synthesis from dietary precursors and re-cycling. The daily turnover of adenosine is very high. Adenosine can act either as a hormone by binding to adenosine receptors, four adenosine receptor subtypes have been identified, and as an intracellular modulator, after transport into the cell by membrane transporter proteins. One of the principal intracellular actions of adenosine is inhibition of the enzyme phosphodiesterase. Extracellular adenosine also has specific neuromodulatory actions on dopamine and glutamate. Selective and nonselective agonists and antagonists of adenosine are available. The tasks of developing, evaluating and exploiting the therapeutic potential of these compounds is still in its infancy. Adenosine has actions in the central nervous system (CNS), heart and vascular system, skeletal muscle and the immune system and the presence of receptors suggests potential actions in the gonads and other organs. Adenosine agonists improve tissue perfusion through actions on vascular smooth muscle and erythrocyte fluidity and they can be used to improve the quality of life in aged dogs. This article reviews the therapeutic potential of adenosine-potentiating drugs in the treatment of age-related conditions in companion animals, some of which may be exacerbated by castration or spaying at an early age.

Proarrhythmic effects of adenosine: one decade of clinical data

In 1989, adenosine was introduced into the American clinical setting as an antiarrhythmic drug for the acute management of reentrant supraventricular tachycardia involving the atrioventricular node. During this decade of use, evidence for proarrhythmic effects of the drug have been documented. In addition to the mostly benign transient episodes of atrial fibrillation, several cases of life-threatening ventricular arrhythmias induced by adenosine have been reported. This article summarizes the proarrhythmic effects of adenosine as they were reported in the literature as well as data from the manufacturer files. The causes of these adverse effects of adenosine are analyzed, and factors to be considered before using the drug are discussed.

Enhanced diagnosis of narrow complex tachycardias with increased electrocardiograph speed

The objective of this study was to determine if the addition of rapid speed (50 mm/s) electrocardiograms (EKGs) improves the clinician's diagnostic accuracy of narrow complex tachycardias when compared to standard speed (25 mm/s) EKGs. We conducted a prospective, comparative trial. Forty-five difficult narrow complex tachycardias (heart rate range: 150-250 beats per minute) were printed at both 25 mm/s and 50 mm/s. Eight board certified emergency physicians initially interpreted the standard speed EKG (standard group) and chose a therapy for the hypothetical patient. These eight participants later interpreted the same 45 EKGs by using both the standard and rapid speed EKGs (rapid group) and again chose a therapy. The gold standard for each EKG was based on the patient's clinical diagnosis and was independently confirmed in all cases by a board-certified cardiologist. The rhythm distribution was as follows: atrial flutter (17), atrial fibrillation (11), paroxysmal supraventricular tachycardia (15), and sinus tachycardia (2). Participants were masked to all clinical information and EKG ratios. Diagnostic accuracy was compared by using McNemar's chi(2) test. Correct diagnosis improved from 226/360 (63%), in the standard group to 257/360 (71%) in the rapid group (difference in means 8.6%, p = 0.002). The incorrect use of adenosine was decreased from 43/240 (18%) in the standard group to 32/240 (13%) in the rapid group (difference in means 4.5%, p = 0.06). In conclusion, correct diagnosis of difficult narrow complex tachycardias was improved when EKGs at both 25 mm/s and 50 mm/s were used for interpretation. It appears that the simple technique of increasing the EKG paper speed, and thus effectively spacing out the rhythm, enhances the diagnostic ability of the observer.

The clinical utility of adenosine in difficult to diagnose tachyarrhythmias

BACKGROUND

The use of intravenous adenosine to help differentiate the origin of tachyarrhythmias has been suggested to be beneficial. However, the benefit of this intervention to physicians with different levels of training in electrocardiographic (ECG) interpretation is unknown.

HYPOTHESIS

The purpose of the study was to determine whether intravenous adenosine improved the diagnostic accuracy of difficult to diagnose tachyarrhythmias when used by physicians with different levels of training in ECG interpretation.

METHODS

We studied 28 consecutive patients presenting with wide and narrow complex tachyarrhythmias, in whom adenosine was given specifically for diagnostic purposes. Two groups of physicians, attending (n = 14) and housestaff (n = 10), reviewed each ECG before and after the administration of adenosine.

RESULTS

For narrow complex tachyarrhythmias, neither physician group derived diagnostic benefit from the use of adenosine. However, for wide complex tachyarrhythmias, the diagnostic accuracy of the housestaff group significantly improved with the use of adenosine (pre = 54%, post = 70%, p < 0.01), while the attending physician group had no significant improvement (pre = 61%, post = 71%, p = NS).

CONCLUSION

This study suggests that adenosine provides useful diagnostic information to physicians less experienced in ECG interpretation when presented with patients having wide complex tachyarrhythmias of uncertain origin.

Sustained ventricular tachycardia in the emergency department

The aim of the study was to evaluate the demographics, haemodynamics, ECG characteristics, underlying disease, tachycardia termination and outcome of patients with sustained ventricular tachycardia (VT). We registered 75 patients presenting with VT (51 male, median age 63) from December 1993 to August 1998 in our emergency department (ED). Seventeen of these patients were haemodynamically unstable (23%), and 58 patients were stable (77%); there was no difference in the tachycardia cycle length (median 320 ms) and QRS width (median 140ms) between the two groups; however, five of the seven patients with polymorphic VT pattern were in the unstable group. Ischaemic heart disease was the underlying disorder in 57 patients (76%). Acute myocardial infarction (AMI) was present in 12 of the 58 stable (21%) compared to 11 of the 17 unstable (65%) patients. In three patients (4%) VT terminated spontaneously, in 34 patients (45%) VT was terminated by first-line intravenous drug therapy, and in 38 patients (51%) including all 17 unstable and 22 stable who failed to respond to the intravenous antiarrhythmic therapy challenge out of 55 patients, VT was terminated by electrical therapy. Within 2 days, 48 patients (64%) were transferred to an open ward, 13 (17%) still needed intensive care, nine (12%) were discharged to home and five (7%) died. Death occurred due to cardiac failure from AMI with extensive anterior wall infarction in three patients, and due to constrictive pericarditis and reocclusion of stented LAD each in one patient. At presentation in the emergency department, the majority of the patients with VT were haemodynamically stable, thus allowing first-line antiarrhythmic drug administration. However, in the course of the disease, half needed electrical therapy for definitive termination of the tachycardia. Therefore, direct current cardioversion must be available in the emergency department. Haemodynamic instability and death occurs significantly more often if VT occurs during the course of AMI.

Clinical features of Wolff-Parkinson-White syndrome

Wolff-Parkinson-White syndrome is the most common form of ventricular preexcitation. Understanding this syndrome is fundamental for anyone interested in learning about arrhythmias. This review addresses (1) the historic sequence of events that led to the understanding of this syndrome; (2) the pathologic, embryologic, and electrophysiologic properties of accessory pathways; (3) the epidemiology and genetics of this syndrome; (4) the clinical diagnosis of this syndrome, with special emphasis on the arrhythmias that patients with ventricular preexcitation are predisposed to; and (5) the therapy for patients with Wolff-Parkinson-White syndrome.

Adenosine triphosphate: established and potential clinical applications

Adenosine 5'-triphosphate (ATP) is a purine nucleotide found in every cell of the human body. In addition to its well established role in cellular metabolism, extracellular ATP and its breakdown product adenosine, exert pronounced effects in a variety of biological processes including neurotransmission, muscle contraction, cardiac function, platelet function, vasodilatation and liver glycogen metabolism. These effects are mediated by both P1 and P2 receptors. A cascade of ectonucleotidases plays a role in the effective regulation of these processes and may also have a protective function by keeping extracellular ATP and adenosine levels within physiological limits. In recent years several clinical applications of ATP and adenosine have been reported. In anaesthesia, low dose adenosine reduced neuropathic pain, hyperalgesia and ischaemic pain to a similar degree as morphine or ketamine. Postoperative opioid use was reduced. During surgery, ATP and adenosine have been used to induce hypotension. In patients with haemorrhagic shock, increased survival was observed after ATP treatment. In cardiology, ATP has been shown to be a well tolerated and effective pulmonary vasodilator in patients with pulmonary hypertension. Bolus injections of ATP and adenosine are useful in the diagnosis and treatment of paroxysmal supraventricular tachycardias. Adenosine also allowed highly accurate diagnosis of coronary artery disease. In pulmonology, nucleotides in combination with a sodium channel blocker improved mucociliary clearance from the airways to near normal in patients with cystic fibrosis. In oncology, there are indications that ATP may inhibit weight loss and tumour growth in patients with advanced lung cancer. There are also indications of potentiating effects of cytostatics and protective effects against radiation tissue damage. Further controlled clinical trials are warranted to determine the full beneficial potential of ATP, adenosine and uridine 5'-triphosphate.

Imaging of adenosine bolus transit following intravenous administration: insights into antiarrhythmic efficacy

OBJECTIVE

To study the effects of the site of intravenous injection of adenosine and to assess the site of action of adenosine in the heart by correlating cardiac effects with bolus transit.

METHODS

Ten patients undergoing routine technetium (Tc-99m) gated blood pool ventriculography consented to the coadministration of intravenous adenosine. The dose of adenosine required to produce heart block during sinus rhythm was determined following antecubital vein administration. This dose (6-18 mg) was mixed with Tc-99m and given first into the same antecubital vein (proximal injection) and then repeated into a hand vein (distal injection). The ECG was recorded and the transit of the bolus was imaged using a gamma camera.

RESULTS

Heart block occurred in all 10 patients (second degree in seven, first degree in three) at (mean (SEM)) 17.5 (1.0) seconds after the proximal injection of adenosine. Distal injection produced heart block in six patients (second degree in two, first degree in four) at 21.9 (4.4) seconds (p < 0.01). In eight of 10 patients the electrophysiological effects were less with distal injection. The onset of heart block was close to the time of peak bolus Tc-99m activity in the left ventricle. Peak bolus activity was delayed (by about three seconds) and the duration of bolus activity in the left ventricle was increased with distal injection compared with proximal injection, at 17.2 (4.2) v 9.2 (3.1) seconds, p < 0.01.

CONCLUSIONS

The lesser electrophysiological effects of adenosine following distal intravenous injections were associated with delay in transit time and dispersion of the bolus. The correlation of adenosine induced heart block with bolus activity in the left heart indicated dependence on coronary arterial delivery of adenosine to the atrioventricular node.

Differential effects of adenosine on focal and macroreentrant atrial tachycardia

INTRODUCTION

The effects of adenosine on atrial tachycardia (AT) remain controversial, and the mechanistic implications of adenosine termination have not been fully established. The purpose of this study was to elucidate the differential effects of adenosine on focal and macroreentrant AT and describe the characteristics of adenosine-sensitive AT.

METHODS AND RESULTS

Thirty patients received adenosine during AT. Tachycardia origins were identified as focal or macroreentrant during invasive electrophysiologic studies. Responses to adenosine were analyzed and characterized as tachycardia termination, transient suppression, or no effect. Electrophysiologic studies demonstrated a focal origin of tachycardia in 17 patients. Adenosine terminated focal tachycardias in 14 patients (dose 7.3 +/- 4.0 mg) and transiently suppressed the arrhythmias in three others (dose 10.0 +/- 6.9 mg). A macroreentrant mechanism was demonstrated in 13 patients; adenosine terminated only one of these tachycardias and had no effect on the remaining 12 patients (dose 10.2 +/- 2.9 mg). Four classes of adenosine-sensitive AT were identified. Class I consisted of nine patients with tachycardia arising from the crista terminalis; these tachycardias also terminated with verapamil (4/4). Class II consisted of four patients with repetitive monomorphic AT arising from diverse sites in the right atrium; these either slowed or terminated in response to verapamil (2/2). Class III consisted of the three patients with transient suppression and demonstrated electropharmacologic characteristics consistent with an automatic mechanism, including insensitivity to verapamil (2/2). In the one patient with macroreentrant AT that was comprised of decremental atrial tissue, adenosine terminated tachycardia in a zone of decremental slow conduction (Class IV); this tachycardia slowed with verapamil.

CONCLUSIONS

Adenosine-sensitive AT is usually focal in origin and arises either from the region of the crista terminalis (inclusive of the sinus node) or from diverse atrial sites with an incessant nonsustained repetitive pattern. Although most forms of macroreentrant AT are insensitive to adenosine, rarely macroreentrant AT with zones of decremental slow conduction can demonstrate adenosine sensitivity.

Electrophysiologic effects of adenosine in patients with supraventricular tachycardia

BACKGROUND

We correlated the electrophysiologic (EP) effects of adenosine with tachycardia mechanisms in patients with supraventricular tachycardias (SVT).

METHODS AND RESULTS

Adenosine was administered to 229 patients with SVTs during EP study: atrioventricular (AV) reentry (AVRT; n=59), typical atrioventricular node reentry (AVNRT; n=82), atypical AVNRT (n=13), permanent junctional reciprocating tachycardia (PJRT; n=12), atrial tachycardia (AT; n=53), and inappropriate sinus tachycardia (IST; n=10). There was no difference in incidence of tachycardia termination at the AV node in AVRT (85%) versus AVNRT (86%) after adenosine, but patients with AVRT showed increases in the ventriculoatrial (VA) intervals (13%) compared with typical AVNRT (0%), P<0.005. Changes in atrial, AV, or VA intervals after adenosine did not predict the mode of termination of long R-P tachycardias. For patients with AT, there was no correlation with location of the atrial focus and adenosine response. AV block after adenosine was only observed in AT patients (27%) or IST (30%). Patients with IST showed atrial cycle length increases after adenosine (P<0.05) with little change in activation sequence. The incidence of atrial fibrillation after adenosine was higher for those with AVRT (15%) compared with typical AVNRT (0%) P<0.001, or atypical AVNRT (0%) but similar to those with AT (11%) and PJRT (17%).

CONCLUSIONS

The EP response to adenosine proved of limited value to identify the location of AT or SVT mechanisms. Features favoring AT were the presence of AV block or marked shortening of atrial cycle length before tachycardia suppression. Atrial fibrillation was more common after adenosine in patients with AVRT, PJRT, or AT. Patients with IST showed increases in cycle length with little change in atrial activation sequence after adenosine.

Catecholamine facilitated reentrant ventricular tachycardia: uncoupling of adenosine's antiadrenergic effects

INTRODUCTION

Adenosine has no direct electrophysiologic function in ventricular tissue, but in the presence of cyclic adenosine monophosphate (cAMP), stimulation exerts a potent antiadrenergic effect. This effect has been exploited in the recognition and treatment of ventricular tachycardia (VT) due to cAMP-mediated triggered activity and automaticity, which are respectively terminated and suppressed by adenosine. However, the effects of adenosine on catecholamine-facilitated reentrant VT are unknown. A pivotal issue is whether termination of VT with adenosine is mechanism specific, or whether it represents a nonspecific antiadrenergic effect. The purpose of this study, therefore, was to define the effects of adenosine in a well-characterized group of patients with catecholamine-facilitated reentrant VT.

METHODS AND RESULTS

Fourteen patients with catecholamine-facilitated reentry were studied. In the 12 patients with structural heart disease (including two with arrhythmogenic right ventricular dysplasia), adenosine (260 to 550 microg/kg) failed to slow or terminate VT. Two patients without structural heart disease had intrafascicular tachycardia confined to the left posterior fascicle, a calcium-dependent, verapamil-sensitive arrhythmia. In the absence of isoproterenol, verapamil terminated VT but adenosine did not. However, when isoproterenol was subsequently required for facilitation of tachycardia, adenosine terminated VT in both patients.

CONCLUSION

Adenosine has no antiadrenergic (antiarrhythmic) effect in patients with catecholamine-facilitated VT due to structural heart disease. Patients with verapamil-sensitive, left posterior intrafascicular reentry have an unusual dual response to adenosine. In the unstimulated state, adenosine has no effect on basal inward calcium current and, therefore, no effect on VT. However, when induction of VT requires amplification of the inward calcium current through stimulation of cAMP, adenosine sensitivity of VT becomes manifest. These results indicate that with few exceptions, termination of VT with adenosine is strongly suggestive of a cAMP-mediated triggered mechanism rather than reentry.

Role of pulmonary C fibers in adenosine-induced respiratory inhibition in anesthetized rats

The clinical use of adenosine is commonly associated with pulmonary side effects, namely dyspnea, that suggest the possible involvement of bronchopulmonary sensory afferents. Our objective in this study was to characterize the effects of adenosine on breathing and to determine whether the vagal pulmonary afferents play a role in mediating these effects. We measured respiratory and cardiovascular changes in anesthetized, spontaneously breathing rats after bolus injections of adenosine at therapeutic doses. Right atrial injection of adenosine (0.04-0.6 mg/kg) elicits, in a dose-dependent manner, a pulmonary chemoreflex-like response consisting of a delayed apnea, bradycardia, and hypotension. In contrast, the classic capsaicin-elicited pulmonary chemoreflex occurs immediately after injection. Perineural capsaicin treatment of the cervical vagi blocked the adenosine-induced respiratory inhibition. Left ventricular administration of adenosine failed to elicit an apneic response. Pretreatment with the adenosine A1-receptor antagonist 8-cyclopentyl-1,3-dipropylxanthine attenuated the adenosine-induced apnea. These results indicate that adenosine elicits a respiratory inhibition via stimulation of pulmonary C fibers and that activation of the A1-receptor is probably involved. It is unclear, however, what accounts for the exceedingly long latency in this response.

Analysis of the treatment of spontaneous sustained stable ventricular tachycardia

OBJECTIVES

To determine the termination rate of spontaneous sustained stable ventricular tachycardia (SSSVT) as a function of the first and second therapeutic interventions used, and to determine factors associated with successful termination.

METHODS

A multihospital, retrospective analysis of the treatment of patients with SSSVT was performed. The setting included 2 urban county hospitals, 2 urban private hospitals, and a Veterans Affairs hospital. Cases were identified by discharge diagnosis and ECG characteristics, and confirmed by electrophysiology study or ECG criteria.

RESULTS

There were 40 cases of SSSVT identified. Excluding adenosine, 35 patients were treated with lidocaine as a first intervention. The rate of termination with lidocaine bolus was 17% (6 of 35) (95% CI 7-34%). Regarding the 35 patients initially treated with lidocaine, the odds of termination of SSSVT were 11 times greater in those without a history of previous myocardial infarction (MI) than in those with a history of MI (95% CI 0.96-551). Of the 29 patients who failed initial lidocaine treatment, 23 were treated with a second lidocaine bolus, with a termination rate of 18% (4 of 22) (95% CI 5-40%). Only 2 patients with sustained ventricular tachycardia had a concurrent MI, and the tachycardia was unresponsive to initial lidocaine bolus in both cases. Fifteen patients received adenosine with no tachycardia terminations and no significant adverse effects.

CONCLUSIONS

The rate of SSSVT termination with lidocaine was low, particularly in patients with a history of Mi.

Role of adenosine in the diagnosis and treatment of tachyarrhythmias in pediatric patients

Tachyarrhythmias are common rhythm disturbances in infants and children. Despite the availability of diagnostic criteria arrhythmias are sometimes commonly misdiagnosed. Recent reports suggest that an endogenous purine nucleoside, adenosine, has a diagnostic effect in narrow QRS complex tachycardias, in addition to terminating supraventricular tachycardia involving the atrioventricular node. This report reviews the authors' experience with the use of adenosine for diagnosis of narrow and wide complex tachyarrhythmias in children. Adenosine was administered to 43 patients with several types of tachyarrhythmias (mean age, 8.3 +/- 5.24 years). Nineteen patients had structural or acquired heart disease. Of the 43 patients there were 28 (65%) several different types of narrow QRS complex tachycardia and 14 (33%) ventricular arrhythmias. One patient (2%) had long QT. Adenosine terminated supraventricular tachycardia, in 11 of 12 patients (92%), ventricular tachycardia in five of eight patients (63%), and transiently terminated premature ventricular contractions in two of six patients (33%). The diagnostic ability of adenosine was perfect in eight supraventricular tachycardia. In these eight cases the tachycardia mechanism was unclear before the administration of adenosine, which demonstrated three cases of sinus tachycardia, three of atrial flutter, one of atrial fibrillation and one of atrial fibrilloflutter. Confirmation of the primary diagnosis by adenosine was perfect in five tachyarrhythmias including three cases of atrial flutter, one of atrial fibrillation and one of ectopic atrial tachycardia. The average effective dose of adenosine was 212 micrograms/kg (range, 100-400 micrograms/kg). There were no serious side-effects except transient dyspnea, chest pain and flushing. These findings demonstrate adenosine to be helpful and safe in the diagnosis of tachyarrhythmias.

Adenosine as an antiarrhythmic agent

Adenosine produces acute inhibition of sinus node and atrioventricular (AV) nodal function. This profound but short lived electrophysiologic effect makes adenosine a suitable agent for treating supraventricular tachycardias (SVT) that incorporate the sinus node or AV node as part of the arrhythmia circuit, or for unmasking atrial tachyarrhythmias or ventricular pre-excitation. Its antiadrenergic properties also make it an effective agent for use with some unique atrial and ventricular tachycardias. Appropriate dosing and rapid bolusing with intravenous administration is required. Recognition of infrequent proarrhythmic risks and potential drug interactions with xanthine derivatives and dipyridamole should maximize its safe and effective use. This review will highlight adenosine's mechanism of action, administration, clinical indications, efficacy, and risks when used in tachyarrhythmic management.

Current concepts in cardiopulmonary resuscitation

The "chain of survival" is important in the resuscitation of a patient who has had a cardiac arrest. The provision of Basic Life Support (BLS) and Advanced Cardiac Life Support (ACLS) is essential in this "chain of survival." Both BLS and ACLS have undergone several revisions since their initial inception. This article reviews (1) the current established and investigational issues of cardiopulmonary resuscitation, (2) the incidence and outcomes of anesthesia-related cardiac arrest, (3) the use of cardiopulmonary bypass in resuscitation, and (4) cerebral protection during and after resuscitation.

Dose and rate-dependent effects of adenosine on atrial action potential duration in humans

Adenosine provokes atrial fibrillation (AF) in some patients with paroxysmal supraventricular tachycardia (PSVT). Which patients are more susceptible to develop atrial fibrillation after the administration of adenosine to terminate PSVT is unknown. We prospectively measured atrial action potential duration (APD) at incremental doses of 3, 6, and 12 mg of adenosine at paced cycle lengths (CLs) of 600, 500, and 400 ms in 25 patients. Bolus injection of adenosine decreased APD at 90% repolarization in a dose- and rate-dependent manner. During paced CLs of 600, 500, and 400 ms, decreases of 8%, 13%, and 19% (p < 0.05), respectively, were found after bolus administration of 3 mg of adenosine. After 6 mg of adenosine, the APD shortened by 12%, 19%, (p < 0.05), and 27% (p < 0.01), respectively. After 12 mg of adenosine, the APD shortened by 15%, 27% (p < 0.05), and 38% (p < 0.01), respectively. Transient AF occurred in 4 of 25 (16%) patients, all during paced CLs of 400 ms, and after adenosine 6 mg in one patient and 12 mg in three patients. Adenosine shortens atrial action potential duration in a dose- and rate-dependent manner. Whether patients with faster rates during PSVT and those given higher doses of adenosine are more prone to develop atrial fibrillation remains to be determined.

Adenosine in wide-complex tachycardia

The use of adenosine as a therapeutic and diagnostic tool in wide-complex tachycardia is suggested in the current Advanced Cardiac Life Support (ACLS) guidelines. The ACLS guidelines are now 4 years old, and new information on the safety and efficiency of adenosine in wide-complex tachycardia is available. We review the ACLS recommendations in light of the current available literature. In general, the ACLS recommendations remain reasonable with some important caveats.