AV blocks

Verapamil (Table 1), the first slow channel calcium blocker synthesized to selectively inhibit the transmembrane influx of calcium ions into cells, lowers blood pressure in hypertensive patients having good organ perfusion particularly with increased renal blood flow. Sustained-release verapamil for once a day dosing is available for the treatment of hypertension. Constipation is a prominent side effect. Headache, dizziness, and edema are frequent and verapamil can sometimes cause AV conduction disturbances and AV block. Verapamil should not be used in combination with -adrenoceptor blockers because of the synergistic negative effects on heart rate and contractile force. 

Cardiac glycosides have a small ratio of toxic to therapeutic concentration. Possible adverse effects are nausea, vomiting, abdominal pain, diarrhoea, fatigue, headache, drowsiness, colour vision disturbances, sinus bradycardia, premature ventricular complexes, AV-block, bigeminy, atrial tachycardia with AV-Block, ventricular fibrillation. There are several mechanisms relevant for their toxic action (Table 2). 

The hydantoins are contraindicated in patients widi known hypersensitivity to die drug s. Phenytoin is contraindicated in patients widi sinus bradycardia, sinoatrial block, second and diird degree AV block, and Adams-Stokes syndrome it also is contraindicated during pregnancy (ediotoin and phenytoin are Pregnancy Category D) and lactation. Ediotoin is contraindicated in patients widi hepatic abnormalities. 

The cardiotonics are contraindicated in patients with known hypersensitivity, ventricular failure, ventricular tachycardia, or AV block and in the presence of digitalis toxicity. 

Type II second-degree or third-degree atriovetricular (AV) block present... 

In randomized, controlled, clinical trials, calcium channel blockers were as effective as p-blockers at preventing ischemic symptoms. Calcium channel blockers are recommended as initial treatment in IHD when /3-blockers are contraindicated or not tolerated. In addition, CCBs may be used in combination with /3-blockers when initial treatment is unsuccessful. However, the combination of a (1-blocker with either verapamil or diltiazem should be used with extreme caution since all of these drugs decrease AV nodal conduction, increasing the risk for severe bradycardia or AV block when used together. If combination therapy is warranted, a long-acting dihydropyridine CCB is preferred. (3-Blockers will prevent reflex increases in sympathetic tone and heart rate with the use of calcium channel blockers with potent vasodilatory effects. 

Second- or third-degree AV block for diltiazem or verapamil... 

First-degree AV nodal blockade occurs due to inhibition of conduction within the upper portion of the node.15 Mobitz type I second-degree AV nodal blockade occurs as a result of inhibition of conduction further down within the node.12,15 Mobitz type II second-degree AV nodal blockade is caused by inhibition of conduction within or below the level of the bundle of His.12,15 Third-degree AV nodal blockade maybe a result of inhibition of conduction either within the AV node or within the bundle of His or the His-Purkinje system.12,15 AV block may occur as a result of age-related AV node degeneration. 

Symptoms of bradyarrhythmias such as second- or third-degree AV block consist of dizziness, fatigue, lightheaded ness, syncope, chest pain (in patients with underlying myocardial ischemia), and shortness of breath and other symptoms of heart failure (in patients with underlying left ventricular dysfunction). 

Determine whether the patient is taking any drugs known to cause AV block. 

In patients with second- or third-degree AV block due to underlying correctable disorders (such as electrolyte abnormalities or hypothyroidism), management consists of correcting those disorders. 

Adenosine Chest pain, flushing, shortness of breath, sinus bradycardia/AV block... 

Amiodarone IV Hypotension, sinus bradycardia Oral Blue-grey skin discoloration, photosensitivity, corneal microdeposits, pulmonary fibrosis, hepatotoxicity, sinus bradycardia, hypo- or hyperthyroidism, AV block... 

Diltiazem Hypotension, sinus bradycardia, heart failure exacerbation, AV block... 

Propranolol Hypotension, bradycardia, AV block, heart failure exacerbation3... 

Sotalol Sinus bradycardia, AV block, fatigue, torsades de pointes... 

On the basis of ECG findings, AV block is usually categorized into three different types (first-, second-, or third-degree AV block). 

Propafenone Dizziness, fatigue, bronchospasm, headache, taste disturbances, nausea, vomiting, bradycardia or AV block, aggravation of underlying HF, conduction disturbances, or ventricular arrhylhmias... 

Amiodarone Tremor, ataxia, pareslfresia, insomnia, corneal microdeposits, optic neuropathy/neuritis, nausea, vomiting, anorexia, constipation, TdP (<1%), bradycardia or AV block (IV and oral use), pulmonary fibrosis, liver function test abnormalities, hepatitis, hypothyroidism, hyperthyroidism, photosensitivity, bluegray skin discoloration, hypotension (IV use), phlebitis (IV use)... 

Chronic symptomatic AV block warrants insertion of a permanent pacemaker. Patients without symptoms can sometimes be followed closely without the need for a pacemaker. 

Diltiazem and verapamil can cause cardiac conduction abnormalities such as bradycardia, AV block, and heart failure. Both can cause anorexia, nausea, peripheral edema, and hypotension. Verapamil causes constipation in about 7% of patients. 

Ipratropium is used in bradycardia and AV-block, respectively, to raise heart rate and to facilitate cardiac impulse conduction. As a quaternary substance, it does not penetrate into the brain, which greatly reduces the risk of OIS disturbances (see below). Relatively high oral doses are required because of an inefficient intestinal absorptioa... 

Indications. Verapamil is used as an antiarrhythmic drug in supraventricular tachyarrhythmias. In atrial flutter or fibrillation, it is effective in reducing ventricular rate by virtue of inhibiting AV-conduction. Verapamil is also employed in the prophylaxis of angina pectoris attacks (p. 308) and the treatment of hypertension (p. 312). Adverse effects Because of verapamil s effects on the sinus node, a drop in blood pressure fails to evoke a reflex tachycardia Heart rate hardly changes bradycardia may even develop. AV-block and myocardial insufficiency can occur. Patients frequently complain of constipation. 

Signs of intoxication are (1) cardiac arrhythmias, which under certain circumstances are life-threatening, e.g., sinus bradycardia, AV-block, ventricular extrasystoles, ventricular fibrillation (ECG) (2) CNS disturbances — altered color vision (xanthopsia), agitation, confusion, nightmares, hallucinations (3) gastrointestinal — anorexia, nausea, vomiting, diarrhea (4) renal — loss of electrolytes and water, which must be differentiated from mobilization of accumulated edema fluid that occurs with therapeutic dosage. 

---