Atrioventricular block causes

Vidal Company A, Rodriguez Martin A, Barrio Merino A, Lorente Garcia-Maurino A, Garcia Llop LA. Bloqueo A-V por intoxicacion con metoclopramida. [Atrioventricular block caused by metoclopramide poisoning.] An Esp Pediatr 1991 34(4) 313-14. 

Cardiovascular Predictors of advanced atrioventricular block caused by adenosine during stress myocardial perfusion imaging... 

Amiodarone is contraindicated in patients with sick sinus syndrome and may cause severe bradycardia and second-and third-degree atrioventricular block. Amiodarone crosses the placenta and will affect the fetus, as evidenced by bradycardia and thyroid abnormalities. The drug is secreted in breast milk. 

The most important toxic effects reported for calcium channel blockers are direct extensions of their therapeutic action. Excessive inhibition of calcium influx can cause serious cardiac depression, including cardiac arrest, bradycardia, atrioventricular block, and heart failure. These effects have been rare in clinical use. 

The pharmacokinetic properties of these drugs are set forth in Table 12-5. The choice of a particular calcium channel-blocking agent should be made with knowledge of its specific potential adverse effects as well as its pharmacologic properties. Nifedipine does not decrease atrioventricular conduction and therefore can be used more safely than verapamil or diltiazem in the presence of atrioventricular conduction abnormalities. A combination of verapamil or diltiazem with 3 blockers may produce atrioventricular block and depression of ventricular function. In the presence of overt heart failure, all calcium channel blockers can cause further worsening of heart failure as a result of their negative inotropic effect. Amlodipine, however, does not increase the mortality of patients with heart failure due to nonischemic left ventricular systolic dysfunction and can be used safely in these patients. 

Adenosine causes flushing in about 20% of patients and shortness of breath or chest burning (perhaps related to bronchospasm) in over 10%. Induction of high-grade atrioventricular block may occur but is very short-lived. Atrial fibrillation may occur. Less common toxicities include headache, hypotension, nausea, and paresthesias. 

Following septal ablation, patients should be monitored in a coronary care unit for 24 to 48 hours and the temporary pacing wire should be removed at the end of this period in the absence of atrioventricular block. Patients may then be transferred to a telemetry unit for monitoring of arrhythmias. Total hospitalization is usually for three to five days to monitor for occurrence of complete heart block that would require a permanent pacemaker. A sizeable infarction is induced with alcohol ablation and causes creatinine phosphokinase to peak at 1000 to 1500 one day after the ablation. Patients should be maintained on aspirin indefinitely. 

Ranitidine is generally well tolerated but may occasionally cause diarrhoea and other gastrointestinal disturbances, altered liver function tests, headache, dizziness, rash and tiredness. Other rare side-effects include acute pancreatitis, bradycardia, atrioventricular block, confusion, depression and hallucinations, particularly in the very ill or elderly. 

A 36-year-old man became hypomanic after lithium was withdrawn because of symptomatic first-degree atrioventricular block (although, how first-degree block could have caused symptoms is unclear) (134). 

In terms of its potential for inducing cardiac dysrhythmias, cannabis is most likely to cause palpitation due to a dose-related sinus tachycardia. Other reported dysrhythmias include sinus bradycardia, second-degree atrioventricular block, and atrial fibrillation. Also reported are ventricular extra beats and other reversible electrocardiographic changes. 

The causes of syncope in patients with Alzheimer s disease treated with donepezil have been reported in 16 consecutive patients (12 women, 4 men) with Alzheimer s disease, mean age 80 years, who underwent staged evaluation, ranging from physical examination to electrophy-siological testing (54). The mean dose of donepezil was 7.8 mg/day and the mean duration of donepezil treatment at the time of syncope was 12 months. Among the causes of syncope, carotid sinus syndrome (n = 3), complete atrioventricular block (n = 2), sinus node dysfunction (n = 2), and paroxysmal atrial fibrillation (n = 1) were diagnosed. No cause of syncope was found in six patients. Non-invasive evaluation is recommended before withdrawing cholinesterase inhibitors in patients with Alzheimer s disease and unexplained syncope. 

Lithium may cause cardiac effects including T-wave flattening or inversion (up to 30% of patients), atrioventricular block, and bradycardia. If a patient has preexisting cardiac disease, a cardiologist should be consulted and an electrocardiogram obtained at baseline and regularly during therapy. 

The heart may be affected by both muscarinic and nicotinic effects. In the former, stimulation of the parasympathetic nerve endings, while in the latter, excess ACh on the nicotinic receptors, is of importance. The cardiovascular effects are tachycardia caused by the overstimulation of the sympathetic system, bradyarrhythmias, atrioventricular block, hypotension and QT prolongation, VF, and TdP (Grmec et al, 2004). 

The most common cardiac effects are atrioventricular block, sinus bradycardia, and ventricular extra beats. Occasionally serious dysrhythmias occur (SEDA-17, 219), including ventricular fibrillation (15). ATP can cause transient atrial fibrillation (16). Chest pain occurs in 30-50% of patients and dyspnea and chest discomfort in 35-55%. Chest pain can occur in patients with and without coronary artery disease, and the symptoms are not always tjrpical of cardiac pain. 

The incidence of atrioventricular block has been reported in 600 consecutive patients who underwent stress myocardial perfusion imaging with adenosine (140 micrograms/kg/minute for 6 minutes), and of whom 43 had first-degree heart block before adenosine and 557 had a baseline PR interval less than 200 ms (Table 1) (31). The heart block in all cases was of short duration, was not associated with any specific symptoms, and in no case required specific treatment. The risk of atrioventricular block during adenosine infusion was not increased by the presence of other drugs that might have caused atrioventricular block (digitalis, beta-blockers, diltiazem, verapamil). 

Cardiac dysrhythmias induced by anticonvulsants are rare and occur mainly in patients other than those known to be at high risk of sudden death (14). Phenytoin has been rarely associated with bradydysrhythmias, almost exclusively after intravenous dosing, and some of these have been fatal. Hypotension can also complicate intravenous phenytoin. Carbamazepine can depress cardiac conduction, mostly in elderly or otherwise predisposed patients. Third-degree atrioventricular block occurred in one patient with pre-existing right bnndle branch block treated with topiramate, but a cause-and-effect relation was uncertain (SEDA-21, 76). 

Three cases of carbamazepine-induced Stokes-Adams attacks caused by intermittent total atrioventricular block, sinoatrial block with functional escape rhythm, and intermittent asystole have been described it was suggested that cardiac conduction should be assessed if syncope or changes in seizure tjrpe occur in patients taking carbamazepine (5). 

Digitalis can cause supraventricular extra beats or tachycardia. The combination of such dysrhythmias with atrioventricular block is particularly suggestive of digitalis toxicity and carries a high mortality rate (3,36). Rarely atrial fibrillation (37) and atrial flutter (38) may be attributed to digitalis toxicity. The frequency of atrioventricular nodal block is mentioned above. 

Overdose of digoxin in a neonate caused complete atrioventricular block and cardiogenic shock, which were completely reversed within 4 hours after administration of the first dose of antidigoxin antibody a second dose was given 48 hours later, when first-degree atrioventricular block occurred (180). 

Clonidine causes sinus bradycardia and atrioventricular block, as illustrated by two cases, one a 10-year-old boy (6) and the other a 71-year-old woman (7), who developed Wenckebach s phenomenon. Clonidine was also studied in seven patients subjected to electrophysiological studies after 5 weeks of therapy (8). It slowed the sinus rate and increased the atrial pacing rate, producing Wenckebach s phenomenon, indicating depressed function of the sinus and AV nodes. 

A 20-year-old man taking ranitidine 300 mg/day had a brief episode of syncope. The only abnormal finding was first-degree atrioventricular block, which disappeared after withdrawal of ranitidine. Rechallenges on two separate occasions produced recurrence of asymptomatic first-degree atrioventricular block, but cimetidine 400-800 mg/day and famotidine 40-80 mg/day caused no electrocardiographic abnormalities. 

Complete atrioventricular block occurred in a 10-year-old child with a history of hypertension, severe renal dysfunction, incomplete right bundle branch block, and a ventricular septal defect that had been repaired at birth (10). After slow induction with sevoflurane and nitrous oxide 66%, complete atrioventricular block occurred when the inspired sevoflurane concentration was 3% and reverted to sinus rhythm after withdrawal of the sevoflurane. The dysrhjrthmia recurred at the end of the procedure, possibly caused by lidocaine, which had infiltrated into the abdominal wound, and again at 24 hours in association with congestive cardiac failure following absorption of peritoneal dialysis fluid. 

A serious bradydysrhythmia with complete atrioventricular block occurred after some months of conventional verapamil at normal doses and dose-adjusted digoxin in a 72-year-old woman with chronic renal insufficiency of unknown cause the atrioventricular block resolved after 2 hours of hemodialysis (8). 

A careful haseline physical examination, ECG, and laboratory work-up are essential. Underlying ECG changes (U waves, prolonged QT interval, or flattened T waves) secondary to hypokalemia or bradycardia and atrioventricular block from starvation may be present. AU antidepressants can cause seizures thus a careful risk-benefit assessment is warranted if the patient has predisposing factors such as a personal or family history of seizures, cerebrovascular disease, or alcohol or sedative-hypnotic withdrawal. 

Atrioventricular block. There are many types of AV block, such as a first-degree block in which atrial impulses are delayed in the AV conduction to the ventricle. This is shown on the ECG as a prolongation of the PR interval. Digitalis toxicity or excessive K+ levels can be causative. 

The main effect of atropine on the heart is the alteration of the rate. At low doses, the rate is slowed (bradycardia) without a change in blood pressure or cardiac output. Higher doses cause an increase in pulse rate (tachycardia). Atropine may be used in the initial treatment of a myocardial infarction or high-grade atrioventricular block. 

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