Limited clinical utility of Holter monitoring in patients with palpitations or altered consciousness: analysis of 8973 recordings in 7394 patients. 
To determine the clinical utility of 24 hour Holter monitoring by measuring the frequency of candidate arrhythmias recorded during the investigation of palpitations and altered consciousness.  Of 9,729 Holter recordings, reports were available in 8,973 (92.2%) performed in the 7394 patients who comprise the study group.  The mean age of the study group was 66 +/- 19 years and 56.4% were women.  The most common indications were altered consciousness (41.7%) and palpitations (36.2%).  Among patients with palpitations and sinus rhythm (n=2688), recordings were normal in 2247 (83.6%).  Abnormalities included paroxysmal atrial fibrillation (PAF, 6.6%), narrow complex tachycardia (NCT, 2.8%) nonsustained or sustained ventricular tachycardia (NSVT/VT, 2.6%).  Among patients with altered consciousness (n=3075), recordings were normal in 2589 (84.2%).  Abnormalities included PAF (9.5%), NCT (2.6%), NSV/VT (0.2%), pause >2.8s (2.2%) and high degree AV block (1.3%).  The diagnostic yield of Holter monitoring was particularly low in patients aged < or =50 years, of whom 93.1% had palpitations and 95.3% had altered consciousness had normal recordings.  The diagnostic utility of Holter monitoring in patients being investigated for palpitations and altered consciousness is very limited, particularly in young patients for whom alternative diagnostic methods should be considered.