A man with breathlessness whose lungs were clear on auscultation

A 57 year old man with diabetes was admitted for breathlessness. His ECG initially showed sinus rhythm with first degree heart block. All the complexes in the limb leads, and most of the chest leads, were of low voltage. A repeat ECG a few hours later showed the same low voltage complexes and a slow regular rhythm of 38 beats per minute. The rhythm was suggestive of an escape ventricular rhythm. P waves could not be identified consistently in the ECG tracing.

Investigations showed that he had advanced renal failure with a serum creatinine of more than 600umol/L. The serum sodium and potassium were normal.

His lungs were clear on auscultation in spite of his breathlessness and the presence of distended neck veins in the neck and a palpable tender liver. His x-ray chest showed significant cardiomegaly. The lungs were clear with reduced vascular markings.

He was treated as congestive cardiac failure due to dilated cardiomyopathy and complete heart block, diabetes, and end stage renal failure.

Discussion
Is the diagnosis of dilated cardiomyopathy correct?
A large heart shadow on the x-ray chest, the presence of congestive cardiac failure and the absence of obvious causes for the heart failure can be the reasons for a diagnosis of cardiomyopathy. However, in this patient with signs of heart failure, the cardiomegaly, the low voltage complexes in the ECG, and the absence of adventitious sounds on auscultation of the lungs should make one consider the diagnosis of a pericardial effusion.

What could be the cause of the pericardial effusion?
The best guess in this situation will be uremic pericarditis with effusion.

Is the slow heart rate due to complete heart block?
I am not in favour of interpreting the ECG as complete heart block because the P waves are not seen regularly. The absence of P waves and a slow regular ventricular rhythm suggests the diagnosis of sick sinus syndrome. Hyperkalemia can be a reason for absence of P waves in the ECG, but that is not the reason in this patient because the serum potassium was normal.

What is the finding in the ECG that differentiates a slow ventricular rate due to complete heart block from sick sinus syndrome?
In complete heart block, the atrial rate is always faster than the ventricular rate and this can be seen from the P wave rate and the QRS rate. In sick sinus syndrome, there will often be no P waves and the slow ventricular rate is either because of a junctional escape rhythm or an escape ventricular rhythm.